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N-P Jewelry Dictionary

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naat - A thin, flat, twinned diamond crystal; also a Dutch term for the seam where the two individuals join. "Cross naat" is a multiple twinning.

nacre - (nay'ker) The iridescent outer layers of a pearl or cultured pearl, a combination of tiny, six-sided crystals of aragonite, held in a weblike deposit of organic conchiolin. The transparency, shape and placement of the crystals cause both luster and iridescence. The maximum cultivation time for most salt-water Japanese cultured pearls is 3 years, after which the nacre tends to deteriorate or distribute unevenly. By then, in Ago Bay, the nacre is about ¥1 mm. in thickness, durable and adequate. The nacre coat of many cultured pearls, however, is % mm. or less; such pearls loose luster quickly.

naif - 1. Dutch word for natural. 2. A bright unpolished diamond crystal; in former times in India, such stones were more highly valued than cut stones. Tavernier observes that Oriental cutting in his day merely restored the polish to faces of perfect crystals, with faceting reserved for stones with many inclusions and flaws.

name bar - Distinguishes the barrel bridge from the other bridges in a bar movement; so called because usually the maker's name is engraved on that part. See BAR MOVEMENT.

naphtha - A highly inflammable degreaser rated as being midway between gasoline and benzene.

Nassau pearl - A pink conch pearl.

National Association of Watch and Clock Collectors - Founded in 1944; in 1976 reported more than 14,000 members, in 63 chapters located in the United States and 26 other nations.

National Stamping Act - U.S. Federal law, enacted 1906, controlling quality marks on articles made in whole or part of gold or silver; 1961 amendment requires a registered trademark to accompany a quality mark; 1970 amendment permits suit in civil court against violators.

National Wholesale Jewelers Association - An organization of more than 100 wholesale jeweler firms and more than 150 associate members, manufacturers that distribute through wholesalers rather than directly or through manufacturers' representatives; established in 1907.

natural - An unpolished surface of the original diamond crystal often visible on a short length of the girdle and sometimes other places. The American Gem Society holds that a natural is not a blemish if it is confined to the surface of the girdle, if the girdle width has not been increased to accommodate the natural, if the natural cannot be seen on or directly through the crown, and if the natural does not distort the symmetry of the girdle outline.

natural compensation - In frictional escapements, an approximation to compensation of timekeeping rates in varying temperatures, due to changes in liquidity of the oil between escape wheel teeth and body of cylinder or staff against which locking takes place. See ESCAPEMENTS, FRICTIONAL.

natural error - In adjusting watches to positions, it is impossible to obtain a condition of perfect poise in the weight of the hairspring coils; a heavy point remains, which produces an unavoidable difference in rate in one position compared with rates at three other quarter-positions of the watch; this difference is the "natural error;" its location is usually placed in the pendant-down position, because it is practically impossible to carry a watch in that position.

natural glass - Obsidian, tektites and silica-glass.

natural pearl - A usage which distinguishes genuine from cultured pearls.

natural stone - A naturally occurring stone, as distinct from an imitation, artificial or synthetic stone.

navigator's watch - Sometimes called a captain's watch, having two dialettes, one set to Greenwich or home port time, the other with local time, often with center seconds.

neatsfoot oil - Oil derived from the bones of domestic cattle.

neck-chain - An item of jewelry, generally understood to be a slender, light chain of precious metal, usually suspending a locket or other ornament; this term differs from "necklace" in that the latter comprehends any kind of jewelry, strings of gems, medallions, etc., worn around the neck, regardless of weight.

necklace - A string of jewels, beads or the like, or a metal band or chain worn close round the neck, or low down upon the breast. One of the most primitive of ornaments.

necklet - Short necklace, less than 18" in length.

needle files - Small hand-files used by jewelers and watchmakers. They come in assorted sizes, shapes and cuts, each with a steel extension used as a handle. Length of cuts ranges from 1-3/4 to 4-1/8" and the cuts vary from #00, the coarsest, to #6, the finest. See FILE.

needle gauge - A gauge for measuring diameters of holes in watch jewels, comprising a slim, tapered steel needle on which a jewel is placed and pushed against a stop, when a pointer indicates the hole diameter on a scale set in the handle of the instrument.

needle-spar - An ancient term for aragonite.

needle stone - Sagenitic quartz.

needle testing - Term sometimes used denoting the method of testing fineness of gold with a test-stone, acid and a set of metal points tipped with gold of various karat-fineness, called "needles." See KARAT NEEDLES; TESTING NEEDLES; TOUCHSTONE.

negative crystal - A characteristic inclusion of natural gems; an angular cavity whose edges parallel original or potential crystal faces of the mineral is known as a negative crystal. Such inclusions are to be distinguished from bubbles with rounded outlines.

negative setting - A class of mechanisms for pendant-setting watches, in which a split spring sleeve in the case pendant holds the stem into the mechanism in the watch movement, in position to which it has been shifted by pulling or pushing the crown for either setting, or winding, the watch.

nepheline, nephelite - (neff'ell-een) Or ELAEOLITE, an uncommon mineral characteristic of rocks which are low in silica. It is composed of sodium, aluminum and silica, has a hardness of about 5, a greasy luster and is translucent to opaque, gray, blue-green, brown to brick red. Nepheline refers more specifically to a white to colorless variety often in crystals in volcanic rocks, and these have no gem use. Innumerable inclusions in the elaeolite variety often impart a cat's-eye shimmer to cabochon-cut gems of this material.

nephrite - (neff'rite) A compact calcium magnesium iron amphibole, a member of the increasingly green tremolite to actinolite series. The felted needles are much finer and more compact than in actinolite, however. It is one of the minerals which make up jade, the nephrite member of which has a more restricted color range and its most characteristic shade is "spinach green". It is found in many places, North America, Europe and Asia, as well as in New Zealand. The finest mutton fat Chinese jade is nephrite. See also JADEITE; JADE.

nephritoid - A synonym of JADE.

nest boxes - Small cardboard boxes for jewelers' merchandise, sold in sets, each box fitting into one a size larger to save room in storing stock.

neutral locking - A condition of adjustment in lever escapement in which there is no draw at the moment of drop-lock. See DRAW.

Nevada diamond - Misnomer for an obsidian.

New Guinea shell - Macassar shell.

New Zealand greenstone - Nephrite or misleadingly, serpentine.

New Zealand jade - Nephrite.

Niagara spar - Gypsum, the transparent colorless variety which is found in rock cavities near Niagara Falls, commonly known as selenite.

nickel - An elemental metal of important use in horology and in the jewelry trades. Pure nickel is white, hard, ductile and malleable. In horology and for tableware and other jewelry store merchandise, the principal use of pure nickel is as a constituent of alloys with copper and zinc, to make nickel-silver or German silver; sometimes called by such names as silveroid, silverine, etc., used as the base metal for silver-plated hollowware; in alloys with gold to make white gold, and with iron or steel for special alloys used for some parts of watches and clocks. When alloyed with gold, it makes the latter harder, more ductile and paler; it replaces silver in white gold; it acts as a grain refiner, producing smooth surfaces after annealing or casting.

nickel dermatitis - A local allergic reaction of nickel-sensitive individuals, sometimes caused by the presence of nickel in certain white gold alloys. If nickel is present, a drop of dimethyl-glyoxime and a drop of 10% ammonia water will produce a pink precipitate upon the alloy. Allergies to other gold alloys or to silver or platinum are rare. See BLACK DERMO-GRAPHISM.

nickel silver - Also called German silver because of some color resemblance to the precious white metal; not because of any silver content. Contains copper (48 to 87 per cent), nickel (7 to 32 per cent) and zinc (5 to 36 per cent), and sometimes small amounts of tin, lead or other metals. The nickel or German silver base metal for silver-plated ware is usually composed of copper (65 per cent), nickel (5 to 25 per cent), and zinc (10 to 30 per cent). Blanks for flatware are usually 18 per cent nickel. For hollowware, blanks are usually 18 per cent nickel for use in hotels; 10 per cent nickel for commercial distribution. For Government use, Federal specifications call for 18 per cent nickel for bodies, spouts and handles; 15 per cent nickel for spun articles, and 12 per cent nickel for tips and other small parts, unless white metal is used. See WHITE METAL.

nicks - Small chips along the facet junctions of a cut stone; these are commonly observed in any gem that has been worn for some time.

nicol prisms - Polarizing prisms composed of a sawn, polished and cemented pair from flawless, colorless Iceland spar calcite. Used in all fine polarizing microscopes, they transmit completely polarized colorless light, Polaroid is an inexpensive modern substitute. Nicol prisms were first made and described by William Nicol, in 1828, hence the name.

nicolo - Black or dark brown onyx overlain by a thin bluish white layer.

niello - A kind of decorative work mostly applied to silver, in which a design appears in a blue-black color against the bright silver background. It is produced by engraving the silver; then filling the cut design with a mixture of copper, silver, lead and sulphur. Niello is of ancient Egyptian origin; it reached its greatest vogue during the Middle Ages and the Renaissance, in Russia and Italy; since then its use has spread to other countries. Some American manufacturers have used niello on special order work, for monograms and individual decorations on watch cases and jewelry. Nifty. Trade name for doublets made by Naftule of Geneva, Switzerland; the crowns are synthetic white or yellow sapphire; the pavilions, strontium titanate.

niggerhead mussel - The most important of the fresh water pearl mussels (Quadrula ebena) but not the best pearl producer.

night emerald - Misnomer for peridot, "evening emerald."

nigrine - A high-iron black rutile, which, when cut, resembles a black diamond.

nilion - A grayish to honey brown jasper from the banks of the Nile, used as a gem by the Greeks. One authority thinks it was nephrite.

nippers - One of a class of pliers with cutting blades on the jaws, either exclusively or in combination with jaws for other purposes. They are blades used for cutting wire or rods of small diameter.

nitric acid - A liquid compound of nitrogen, hydrogen and oxygen, HN03, much used in the jewelry trades, for chemical manipulations of precious metals, for testing fineness of old gold, etc. In testing scrap, a drop of nitric acid placed in a notch boils and turns green if the article is brass or copper. Yellow gold of 6K or lower boils nearly as fast. 10K yellow gold darkens. 12K yellow gold shows little reaction. Platinum and stainless steel resist nitric acid.

Nixie tube - Digital display of neon gas in transparent tube containing all the elements of the primary digits 0-9.

noble metals - Metals that are permanent in air, showing no tendency to oxidation under ordinary conditions. The alchemists applied the term to gold and silver, which in their opinion possessed special philosophic virtues, and believed that by proper treatment they could release the noble principles in base metals such as lead or iron, and thereby transmute them into noble metals. The six metals of the platinum group—platinum, palladium, iridium, osmium, rhodium and ruthenium—are now commonly included in the noble metals. All of these metals except silver and palladium resist the action of nitric acid. See PRECIOUS METALS.

noble opal - Precious opal.

noiseless clock - Any clock with a noiseless escapement such as with gut pallets, conical pendulums, etc.

non-magnetic - A classification term applied to watches in which parts, ordinarily made of steel, are made of non-ferrous metals that cannot be magnetized. Under Federal Trade Commission regulations issued in May, 1947, the term "anti-magnetic" may be used to describe a watch which will not vary more than 15 seconds as a result of having been placed in an electrical field of not less than 60 Gauss and kept there at least five seconds each in the vertical (with pendant in any position) and horizontal (with pendant either up or down) positions.

non-magnetic shield - An iron outercase, for carrying a watch where there are heavy electro-magnetic fields, as around electrical machinery, to protect the watch from magnetization. See MAGNETIZATION.

non-nucleated - Pearls which have been stimulated into formation by a bit of foreign mantle material, in place of the usual large mother-of-pearl core of the nucleated cultured pearl. Besides the body colors found in nucleated cultured pearls, fresh water non-nucleated cultured pearls also are light or dark orange, green and brown.

normal period - In adjusting watches to temperature, after being run in heat for 24 hours, they may be run outside of the oven for another 24 hours before being placed in refrigerator for a test in cold; to allow the metals in balance and hairspring to return to their natural form and tension between the heat and cold tests. The rate during this in-between run is called the normal period rate. See ADJUSTMENT.

north daylight - Diamond grading. Illumination from the northern sky between 10 a.m. and noon, on a moderately overcast morning, during the spring or fall of the year. Certain instruments provide soft, diffused lighting closely approximating north daylight.

notch - 1. In the duplex escapement, the slot cut vertically in the balance staff, through which wheel pass during each impulse that is given by the vertical lifting teeth. The function of the notch is analogous to that of the passing-hollow on roller edge of lever escapement. 2. Term used occasionally meaning the fork-slot of a lever escapement. 3. One of the spaces cut out of pallet-yoke in lever escapement, into which a pallet stone is set by means of shellac. See FORK; LEVER ESCAPEMENT.

notch-plate - A disc on a gear-cutting fixture, with notches cut on the edge, to engage a latch for spacing a blank while being cut with gear teeth; differentiated from the universal index-plate, which has circles of holes drilled in its faces, for the same purpose. See INDEX-PLATE.

novaculite - (no-vak'u-lite) An extremely compact and fine-grained variety of grayish white to creamy colored quartz, found near Hot Springs, Ark. It is little used as a gem but makes fine whetstones.

noselite, nosean - One of the lapis lazuli group of minerals.

nuclear watch - Type of watch, patented in 1970 and thereafter, for which the timebase is the decay rate or half-life of radioisotopes. The alpha ray emissions are monitored and divided binarily through integrated circuits, to provide impulse for indexing seconds, minutes, hours and calendric functions.

nucleated cultured pearl - One that was produced by the implantation of a polished bead in a mollusk by man. The round bead used for whole pearls is made of mother-of-pearl shell from a fresh-water mollusk, usually the Pig-toe mussel from the Mississippi River. See NON-NUCLEATED CULTURED PEARL.

nugget - Metal in a lump or irregularly shaped mass; a term usually applied to a lump of gold or silver found so formed by nature. In mining districts, much jewelry is made of nuggets mounted as pins, necklaces, chains, etc. Said to be the largest gold nugget in the world, "The Big Triangle," exhibited in the Kremlin in Moscow, weighs about 81 lbs.

nulled - Ornamented with a convex, rounded decoration differing from a gadroon in that the latter is on a rounded, while the former is on a flat or quarter-round surface.

numeite - (noo'may-ite) Garnierite, named for Noumea, New Caledonia.

nut - On a micrometric watch regulator or on the screw at the lower end of a pendulum rod, a circular tapped metal disc, usually graduated with divisions to aid in making definite changes in the regulation to mean time.

nyf - The outer "skin" of an uncut diamond crystal.


O - A unit measuring the size of smaller American watch movements, such as "O-size," "three-O size;" "ten-O size," etc. See WATCH SIZES.

oblong cut - Same as emerald cut.

observatory bulletin watch - A trade term denoting a watch of exceptional timekeeping performance, proof of which is in a certificate, issued by a national astronomical observatory or scientific bureau, which records the data of tests of that particular watch. Such watches usually command a premium price. National observatories that conduct watch tests may do this for individual owners of watches, also in the form of annual competitions for excellence among various manufacturers of watches.

obsidian - (ob-sidd'ee-an) A natural glass, formed when lava solidified too rapidly for any of the constituents to crystallize. It varies from black to light gray, reddish or greenish in colors; often it is translucent, sometimes iridescent or adularescent. OBSIDIANITE is a term which has been applied to the possibly meteoritic glasses like moldavite, Darwin glass, etc.

occasional impulse - A class of clock escapements which delivers an impulse to the pendulum less frequently than at each beat, thus diminishing interference with freedom of motion of the pendulum. Inventions for this began about 1850; the Shortt clock embodies this principle.

occidental - Because the finest and hardest gem-stones at one time reached Europe from the Far East, the term oriental was used as a prefix to the various colors of corundum and other gems of superior hardness. Conversely, the prefix occidental may mean: a. "True," as occidental amethyst, to distinguish it from the so-called oriental amethyst (purple sapphire), b. More frequently, a less desirable stone of the same variety; for example, occidental agate, cornelian and chalcedony are less translucent varieties, and occidental pearls are from the Atlantic and Pacific coasts of Central America, c. A misnomer for a stone of a less precious class that resembles a more precious class; for example, occidental cat's-eye is a misnomer for quartz with hornblende needle inclusions; occidental topaz, a misnomer for citrine; occidental turquoise, a misnomer for odontolite; occidental diamond, a misnomer for quartz. See ORIENTAL.

occurrence - From a mineralogical viewpoint, the occurrence of a mineral, gem or otherwise, refers to the place and type of deposit in which it is found, as well as its associates. Diamonds "occur" in alluvial deposits and in igneous pipes. Aquamarines and topaz almost invariably "occur" in pegmatite dikes. One might also say that a diamond if found in the schists of Manhattan would be a new "occurrence" for that gem, as would an association of peridot with aquamarine.

ochre - A yellow clayey earth, used in soldering jewelry work, as an antioxidizer; or painted and dried on surfaces prior to soldering, to prevent solder from flowing where not wanted. See YELLOW OCHRE.

octagon - A cushion shape with truncated corners; an emerald cut with deeply cut corners.

octahedron - A crystal form of the cubic, or isometric, system. A common form of diamonds and spinel, it can best be visualized as two four-sided pyramids, joined at their bases.

oculus mundi - Hydrophane.

odd-beat - Watches with balances beating more or less than 18,000 beats per hour are known as odd-beat watches. Less than 18,000 beats, wristwatches of recent design; the standard rate for modern watches is 18,000 beats per hour.

odd-shape crystals - Trade term denoting watch crystals of shape other than round.

odontolite - (o-dont'o-lite) "Bone turquoise," an iron impregnated, blue-colored fossilized bone, which resembles turquoise. Some of the best has come from the tusks of mammoths found in Siberia. The structure of the bone, visible in polished surfaces, enables an easy distinction from the true turquoise. It is also said to lose color and become grayer in artificial light.

oersted - A centimeter-gram-second unit of magnetic intensity, named after Hans Christain Oersted, Danish physicist. Used in the testing of non-magnetic watches.

off color - Diamond grading. A color grading term for diamonds that display a more or less distinct tint of undesirable color, especially yellowish or brownish, when viewed through the table by an experienced eye; it includes the cape or slightly tinted white, tinted white and yellowish grades.

ogee, OG - A type of S-shaped curve of molding with the convex section on top; used on older American clocks.

ogive - The addendum of acting portion of a tooth of a gear-wheel; differentiated from the addendum of a pinion leaf, which is called the rounding. See ADDENDUM; DEDENDUM.

ohm - A unit of electrical resistance in a circuit.

oilcup -1. The concave recess formed around the pivot hole on the upper side of a jeweled bearing, or on the metal of a non-jeweled bearing in a watch or clock, for holding a supply of oil. 2. A small covered cup, of glass or agate, used on the watchmaker's bench to provide a small, frequently renewed supply of oil for use on timepieces.

oiled stones - Jewelry stones which have been soaked in kerosene, Three-in-One oil or some other petroleum product to intensify their color (turquoise, etc.) or to minimize the visibility of open flaws (emeralds, etc.). Might also be applied to amber heated in oil to develop the spangles often seen in modern pale ambers.

oiler - Tools for applying oil to parts of timepieces. The two types used are (1) a blade made of fine gold or steel wire set into a handle, with a flattened point charged with a small quantity of oil by dipping it into a bench-cup, and (2) foundation oilers, holding a supply of oil in the hollow handle, which has an extension in the form of a fine capillary tube through which oil flows to form a droplet at its end, which is touched to the part being oiled. Of the above types, the former is used mostly in repair shops and the latter in watch factories.

oillies - Premier diamonds.

oils - Horology. Liquids used for lubrication of parts of timepieces. The principal types of oils used today are classified as to source, as animal oils, mineral oils, and synthetic oils, such as silicones. See FRICTION; LUBRICATION.

oilsink - A V-shaped cut turned into the part of an arbor in a watch or clock, immediately next to the base of a pivot, to keep oil from overflowing onto the arbor, by capillary action.

oil spots - Greenish spots on oriental pearls, caused by conchiolin knots near the surface.

oilstone - 1. A natural stone used for an abrasive for finishing metal parts of timepieces, etc., and for shaping and sharpening cutting tools. The quarried rock is formed into flat bench-laps; "slips" or hand-laps used as files; wheels used in lathes; and is also pulverized to be used mixed with oil for grinding with metal laps, for finishing watch staffs, etc., preparatory to polishing them with finer abrasives. Most of the natural oilstone used in America comes from Arkansas; the fine-grain stone is marketed as "hard Arkansas," and the coarse-grain Arkansas stone as "Washita" stone. Known to geologists as novaculite, it is a very fine grained quartz, resembling chert but in beds, rather than concretions, as chert would be. 2. Water-worn yellow and red chalcedony pebbles found with diamonds in the Transvaal alluvial deposits.

oil-tempering -1. A process of applying heat to reduce the hardness of a piece of fully hardened steel, in which the steel part is covered with oil, heat applied, and the progressive softening judged by the effect of heat on oil; thicker and thicker smoke appears; flashes of flame next; finally steady flame. 2. In manufacturing watches and clocks, a mass-production method for tempering large quantities of steel parts, which are placed in a pot of oil kept heated under control of an indicating pyrometer. See TEMPERING.

old English cut - single cut.

old European cut - Term for brilliant-cut diamonds with round girdles, produced after the invention in 1891 of power-driven bruting machines; similar to the earlier old mine cut, except for the square or cushion shape of the girdle of the latter. Characterized by heavy crown, small table, large culet, and great overall depth. See OLD-MINE CUT; BRILLIANT CUT.

old gold - Gold articles as bought for junk to be melted and refined and used again in making new goods. See LEMEL; SCRAP; REFINING.

old mine cut - Term originally applied to the high-crowned, small-tabled, square or cushion-shaped brilliant cut diamonds, much in vogue during the 18th and 19th Centuries, which retained much of the original outline and weight of the octahedron rough at the sacrifice of brilliancy. Because stones so cut came from Brazil, they were called "old mine" to distinguish them from diamonds from the newer South African mines which began to be cut with a round girdle by means of mechanical BRUT1NG. The term was later applied to overthick, "lumpy" round diamonds whose crown is higher and whose table is smaller than the present-day brilliant. Old mine cut with 8 additional facets around the culet is known as Brazilian cut. See BRILLIANT CUT; OLD EUROPEAN CUT.

oleic acid - An ingredient in recipes for watch cleaning solutions; a colorless oily liquid.

oligoclase - (o-lig'o-klase) One of the plagioclase feldspar series, with a little more calcium than albite, plus sodium, aluminum and silica. Oligoclase moonstone and oligoclase sunstone are known, but are less common than the orthoclase-albite moonstone and the orthoclase sunstone. There is also a colorless or very pale blue oligoclase found in North Carolina and Kenya, which is occasionally cut.

olive - A faceted bead, derived from the faceted spherical bead by an elongation parallel to the hole. Many modifications of this shape are possible.

olive-hole - A form of hole for a pivot-bearing the cross-section of which shows a variation of diameter at all points of the length of the hole; the least diameter being midway between the ends of the hole, gradually increasing toward each end. The advantages of this over straight-sided holes are (1) less liquid friction retarding motion of pivot when oil has become thickened by age; and (2) a correcting effect on the slightest deviation of the hole from perpendicularity.

olivine - (ol-iv-een') A mineral series, like feldspar, containing, in varying proportions, magnesium, iron, manganese and silica. The only gem in the series is chrysolite, which is also called peridot; it contains about 20 per cent of the iron silicate molecule. Erroneous uses are as follows: Uralian olivine, Siberian olivine, olivine garnet; the common designation "olivines" means demantoid garnets (which, incidentally, are far more desirable and attractive gems; probably the only instance in gemology where the jewelers have perpetuated an error to their disadvantage). See CHRYSOLITE; PERIDOT; DEMANTOID GARNET.

onegite - Light-colored amethyst with needle-like inclusion of goethite, found in geodes on an island in Lake Onega, north of Leningrad.

144 Cut - Modified round brilliant patented in 1966 by Huisman Bros, of New York. To the usual 58 facets are added 48 diamond-shaped facets just beneath the girdle and 38 facets to the girdle.

one-year pearls - Culture pearls with very thin nacre layers.

onyx - (on'iks or own'iks) To the trade, onyx is the equivalent of the mineralogists' chalcedony. As most commonly used, without prefix or suffix, it generally means black chalcedony. The different meanings of this word have become complicated by a long history; today it connotes a variety of banded agate with flat parallel layers. Green onyx is also dyed chalcedony. To the Greeks, onyx was a synonym for alabaster, and their alabaster was banded stalagmitic calcite. Hence, there is justification for such common uses as Brazilian onyx, Oriental onyx, Mexican onyx, cave-onyx and so on. Onyx is derived from a Greek word for nail, which refers to the color bands seen under the finger nail. An onyx lamp or an onyx pen-stand refers to a calcite-aragonite marble variety of onyx (hardness 3); an onyx ring stone refers to the black chalcedony-agate cryptocrystalline variety (hardness 7).

onyx opal - Opal with parallel flat bands.

oolitic - (oh'uh-lit"-ic) Literally, egglike; composed of small rounded masses like a fish roe, a not uncommon texture of some stones.

opal - (oh'pall) A non-crystalline silica gel, solidified into a series of extremely thin films differing slightly in refractivity and containing usually 3 to 13 per cent water. The play of colors characteristic of most of the jewelry store varieties is caused by a regular arrangement of small spheres into a diffraction grating that gives spectral reflections. Hardness, about 5Vi; refractive index very low, 1.45; specific gravity, 2. Precious or noble opal, cut cabochon except for fire opal, includes: WHITE OPAL, BLACK OPAL, HARLEQUIN OPAL, LECHOSOS OPAL, FIRE OPAL and GIRASOL, which see. See also the following varieties of common opal, which have little or no play of color: AGATE OPAL, CACHA-LONG, HYALITE, HYDROPHANE, MILK

opal agate - Alternately banded chalcedony and opal masses.

opal cat's-eye - A brown, yellow, or greenish opal from Yarra-yarra Creek in western Australia shot with narrow white, brown or golden fibrous bands; any opal that shows chatoyancy.

opal glass - A common milky translucent type of glass, which is made by the addition of some fluorite. Imitation pearls have been made by etching opal glass in hydrofluoric acid.

opal jasper - A slightly translucent common opal, colored by iron, and, hence, red, brown, green, yellow, or black.

opal matrix - A white sandstone found with opal in Queensland which contains small opal chips and which is sometimes cut into beads. Also applied in the U.S. to brown limonitic masses with tiny veins of precious opal which are sometimes cut in gemstones.

opal mother - A similar, but darker matrix material, from Hungary. See OPAL MATRIX.

opal onyx - An Honduras precious opal occurrence in which the gem material forms thin bands in common opal.

opalescence - A term used not to indicate similarity to an opal, but a milky or pearly luster.

opalescent chrysolite - Misnomer for cat's-eye.

opalescent sapphire - A sapphire cat's-eye.

opaline - Opal matrix.

opalite - Impure, colored forms of common opal.

opalized wood - See PETRIFIED WOOD. This is a variety of fossil in which the replacing compound has been opal, sometimes common, sometimes precious.

open diamond - A design for watch hands; the pointer end is diamond-shaped with the inside metal cut out.

opener - 1. For watch jeweling, adjustable tools in sets, the jaws of which swedge open the burnished bezel that originally held in a broken jewel, enabling re-burnishing the bezel over edge of a new jewel. 2. A blade in a handle, for opening watch cases.

open-face - A watch case with glass cover over its dial, instead of a metal cover that has to be opened to expose the dial to view. See DEMI-HUNTER; HUNTING CASE.

opening - Horology. 1. The angular measurement of the distance between the two lips of a cylinder escapement, measured with the vertex of the angle in the balance center, and its sides passing through the lips of the cylinder at the points of contact of escape wheel teeth with the cylinder shell. This term is sometimes applied also to the similar parts of lever and verge escapements. See ESCAPEMENTS. 2. In making jewels for pivot bearings, the operation following "piercing" a stone, done with a copper broach charged
with diamond powder, used to give the final form and finish to the hole. See JEWELING.

open setting - A setting with openwork on the sides, permitting the lower portion of the stone to be seen.

open table - Phrase sometimes applied to a diamond table the diameter of which exceeds 60% to 65% the diameter of the girdle. Such stones are termed spread or swindled.

opera length - A necklace 30" in length, double that of a choker. See PRINCESS; CHOKER; MATINEE LENGTH.

operculum - (o-per'-ku-lum) Shell or Chinese cat's-eye. The lid of a (Turbo) snail shell, the disc which closes the opening when the snail is retracted. Those used occasionally as gems are dome-shaped, green or grown, their underside is dark brown, shows a growth spiral, and is covered with a horny substance.

optical anomalies - Gemology. Unusual phenomena, such as strain in an isometric mineral like garnet, which causes it to be birefringent. Synthetic spinel is always birefringent, while natural spinel is usually isotropic.

optical black - An intense black finish for brass, originally used on the inside brass parts of microscopes, etc., but used also for oxidizing engraved lettering on brass nameplates and other jewelry trade work; it is produced by immersion of the work in platinum chloride solution. See OXIDIZING.

optical properties - Light phenomena as they are affected by transparent substances, like the jewelry stones. They differ for each crystalline mineral substance and can be used to identify any stone. Strong dispersion, for example, results in fiery stones; strong double refraction seems to double the edges of the back facets as seen through the table; strong absorption produces colored stones. See DISPERSION; INDEX OF REFRACTION; BIREFRINGENCE; DOUBLE REFRACTION, etc.

optic axis - The direction in a crystal along which no double refraction is observed. In hexagonal and tetragonal crystals it is parallel to the long axis; in the other birefringent systems there are two optic axes, inclined at varying angles at each other. It is the angle between these two axes which is known as 2V and that figure is one of the properties determined in a complete study of a mineral.

orange shellac - The variety of oriental resin best suited for setting palletstone and roller jewels in steel parts of watch escapements; differentiated from white shellac, which is used by jewelers as a cement for securing certain kinds of gems in mountings. In jewelry, used as a cement for holding odd-shaped pieces while setting or engraving. It is dissolved by hot alkali solution, sodium hydroxide (lye), or slowly in alcohol.

orange topaz - Misnomer for citrine quartz.

orange wood - Peeled straight twigs of several varieties of shrubs yielding a hard compact-grained wood, the "pegwood" of commerce; used for finishing the cleaning of pivot holes in timepieces. It is marketed in sizes; sticks averaging one-eighth inch diameter are called watch pegwood; one-fourth inch sticks are called clock-pegwood.

ordinary and rejection cleavage - A shape classification used in the assortment of diamond lots at the mine. Rather low on the scale, followed only by flats, macles, rubbish and bort.

Oregon jade - Misnomer for a green jasper, a green grossular garnet, and the compact variety of vesuvianite more commonly known as californite.

oregonite - Kinradite variety of jasper.

oreide - (o'ree-ide) A variety of brass used for imitating gold and for alloying. A customary oreide formula, among others, is copper 100 parts, tin 17 parts, magnesia 6 parts, ammonium chloride 3.6 parts, crude argol, 9 parts.

organ clocks - A class of striking clocks in which, instead of on bells or gongs, the time signals are sounded by miniature organ-pipes with leather bellows. Cuckoo clocks are the simplest form of organ clocks; more elaborate ones have pipes arranged in scales for playing tunes.

orient - Gemologically speaking, the iridescence seen on the surface of some pearls. See DIFFRACTION.

oriental - Misnomer prefix often applied to corundum having a similar color to the stone described in the second part of the name; this custom began centuries ago in Europe when the harder, more lustrous gemstones came by route of the orient. See OCCIDENTAL. - o. agate. A meaningless term, theoretically used to distinguish better colored agate from paler "occidental" agate. — o. alabaster. The alabaster of the ancients, a banded calcite. See ONYX. — o. almandine. Violet corundum. — o. amethyst. Violet corundum, and violet spinel. - o. aquamarine. Bluish or greenish corundum. - o. carnelian. An earlier differentiation of a more translucent material, as opposed to a variety cut from Idar agates. - o. cat's-eye. Chrysoberyl cat's-eye. — o. chalcedony. The more translucent variety, as opposed to milkier "occidental" chalcedony. - o. chrysolite. Yellowish-green corundum. -o. emerald. Emerald green corundum. - o. girasol Sapphire cat's-eye •- o. hyacinth. Reddish sapphire. - o. jasper. Bloodstone. -o. lapis lazuli. Ordinary deep-colored lapis lazuli. -- o. onyx. Erroneous name for a banded calcite marble. - o. opal. A misleading name formerly applied to the Central European opal which found its way into the market through Constantinople. - o. synthetic alexandrite. A compounding of errors, but it means the imitation alexandrites made from synthetic corundum and spinel. - o. topaz. Yellow sapphire. - o. turquoise. Genuine turquoise; if the prefix were forgotten entirely much confusion would have been avoided; it is a strange anomaly that the genuine should sometimes have to have its genuineness accentuated by the meaningless prefix. o. vermeille. Bright carmine red to reddish sapphire.

oriental baroque - A baroque pearl from an oriental source, usually less distorted than the fresh-water baroques.

oriental pearl - A natural salt water pearl from the Margaritifera oysters of the south and east Pacific, Persian Gulf, Red Sea and other waters. See PEARL.

oriented section - A crystal section made with the optic axis in a definite position, as opposed to a random section made by cutting a slice of a gem without first determining the direction of the optical and crystallographic axes.

original lot - An unsorted batch of stones, as sold by the Diamond Syndicate.

Orleans pastes - Glass and enamel imitation gems developed (1691-1715) by a chemist named Homberg in cooperation with the Regent Orleans, at the Palais Royal, which duplicated Orleans' own collection and many of the royal gems. They are supposed to have been especially fine imitations.

ormier (omier, omar, ormar, omer, ormer) pearl - Abalone mother of pearl and its products.

ormier shell - Abalone.

ormolu - (or-muh-loo) From the French or moulu, literally "ground gold" 1. Gold or gold leaf, ground and readied for gilding another metal; a metal thus gilded. 2. The surface that was obtained on antique French clocks and other objects, which were first mercury-gilded, then coated with a paste of saltpeter, alum, hematite and possibly other red or yellow coloring agents, and heated. 3. An alloy of copper, tin and zinc, its nature affording sharp castings of a color closely resembling yellow gold, usually finished by an exceedingly light gilding, and used for small clock cases, or for ornamental trimmings of wood clock cases; also known misleadingly as "mosaic gold."

ormolu varnish - An imitation-gold varnish, also called "mosaic gold."

Ormskirk escapement - A type of lever escapement used in some clocks made during 19th Century in Liverpool area; contains two escape wheels at right angles to the pallet.

ornamental stone - Generally speaking, any decorative stone; more specifically, something which occurs in quantities too large for it to be termed either precious or semi-precious in the old usage. Malachite and labradorite could be included in this group.

orthoclase - (or'tho-klase) The potash member of the feldspar group apparently crystallizing in the monoclinic system. See MICROCLINE. Orthoclase has a number of gem varieties: adularia, sometimes a moonstone variety; sanidine, a colorless to yellowish transparent variety; and some sunstone.

orthorhombic system - One of the six crystal systems, this has three unequal axes, at right angles to each other. A building brick would be a typical shape for a simple crystal of this sytem. Several gems crystallize in it, topaz, chrysoberyl and peridot, for example.

orthos - The name which has been suggested for a transparent golden-yellow orthoclase from Itrongay and Fianarantsoa, Madagascar.

oscillating weight - The swinging weight on a self-winding watch whose swings crank wheels that wind the mainspring.

oscilloscope - An electronic device in which the pattern of electrical impulses or sounds can be observed on a TV-type screen.

osmium - A hard, white metallic element of the platinum group, possibly the heaviest element known. Specific gravity 22.4 to 22.6; melting point about 2700° C.; chemical symbol Os. In the massive form it is highly resistant to corrosive agents. It can serve as a hardener of platinum, but is rarely so used because when heated it forms a volatile and poisonous oxide. Its alloys, some of which are extremely hard, are used to tip pen points and the like. See PLATINUM GROUP; IRIDOSMINE.

ounce pearls - Poorer grades and smaller sizes usually sold by the ounce.

ounce, Troy - A unit of Troy weight, long used for weighing precious metals. The ounce contains 20 penny-weights each of 24 grains. The Troy pound contains 12 ounces; but quantities of precious metals are customarily expressed in ounces, however great the amount. See TROY WEIGHT.

outer diameter - The full diameter of a gear wheel or pinion; differentiated from the pitch or acting diameter. See ADDENDUM; DEDENUM; GEARING.

out-of-angle - A term used by escapement adjusters in watch factories indicating that the fork moves an unequal angular distance beyond the line of centers on the two sides of the line, with the escapement banked to drop-lock. See all definitions beginning with FORK.

out-of-beat - The result of uneven unlocking and impulses of an escapement, evidenced by intervals of unequal duration between "tick" and "tock."

outside drop - The angular distance traveled by an escape wheel from the instant of the release of a tooth from the L pallet stone until another tooth comes to rest on the R pallet stone. See DROP; LEVER ESCAPEMENT.

oval cut - A modern variation of the brilliant cut, popularized after 1955 by "Oval Elegance," a trademark of Lazare Kaplan & Sons of New York. Also called oval brilliant cut.

oval graver - A graver of lenticular cross-section, turning work. Also used by diamond setters to fit out of round stones.

oval setting - A type of setting similar in design to the Tiffany but made to take an oval stone instead of round.

overbanking - A faulty condition in a lever escapement, in which failure of the guard or safety-action allows the fork to pass over to the wrong side of the line of centers; then the roller jewel, instead of entering the forkslot, comes to rest against the outside of one of the fork-horns, stopping the watch instead of unlocking the escape-wheel for the next impulse. The correction of the fault is to lengthen the dart in double roller escapement, or bend the guard pin toward the roller edge in single roller escapement. See GUARD ACTION.

overcoil - The portion of the outer coil that is bent upward and formed into a terminal curve in a Breguet hairspring. See BREGUET HAIRSPRING; HAIRSPRING.

overcoiling tweezers - Tweezers with tips one of which is in form of a concave arc, the other tip a convex arc fitting into the concave one, for bending terminal curves on overcoils of Breguet hairsprings. See BREGUET HAIRSPRING; OVERCOIL.

over-compensation - In adjustment of a watch to temperature, a condition in which the watch would gain time in heat, and lose time in cold. This is due to having too much weight, too many screws, or too-heavy screws, in the balance rim near the cuts in the balance rim; and the remedy is to move some of the weight (for example, two opposite screws) to positions away from the cuts in the balance rim. See UNDER-COMPENSATION.

overrunning - In a chronometer or a duplex escapement, a fault in which two of the escape wheel teeth may pass through the escapement during one vibration of the balance, caused by faulty adjustment of drop of teeth on impulse pallet.

oversize - A trade term applying to watch repair parts sold by material dealers, in which some dimensions are greater than standard; intended to be reduced in size to obtain a more exact fitting to old parts than could be.

oversprung - The type of watch design in which the hairspring collet is placed on the balance staff above the balance; differentiated from "undersprung."

owl-eye agate - Eye agate with two similar eyes. See CYCLOPS AGATE.

oxblood - A highly valued deep red shade of coral, also known as mow by the Japanese.

ox-eye - Labradorite with a dark schiller color.

ox-eye agate - See OWL-AGATE; CYCLOPS AGATE.

oxidation - The forming of an oxide, as the copper in sterling silver or a karat gold alloy combining, through heat, with oxygen and forming a coating of copper oxide. Not to be confused with the discoloration of silver by sulphur and its compounds.

oxide - A compound of oxygen and another substance, as rust on iron.

oxidizing - A black finish applied to metals, either fully covering the surface, or as background for high-lighted features of a design produced by polishing off the oxidation from higher parts of embossed or engraved work. Oxidizing may be done by immersing silver or other metals in a solution of liver of sulfur (potassium sulphide), or platinum chloride. See BLACK CHROME.

oxygen - A colorless, odorless gaseous element, 0. Used with a fuel gas such as hydrogen, acetylene, propane, methane or coal gas to produce intense heat. A torch is used to combine the gases to generate heat for soldering, welding and melting of metals.


P - Abbreviation for pique in diamond clarity grading.

paar - Pearl oyster bank on the coast of Sri Lanka.

pack-hardening. A method for hardening a number of small steel parts of watches, tools, etc., at one time. The parts are packed in powdered charcoal, enclosed in a metal box; the whole is heated red-hot; then the parts are spilled into water or other quenching medium for hardening. Two advantages are: Avoidance of formation of scale on the work, and time-saving over separate heating of a number of pieces.

packing - In waterproof watches, the pierced washer of prepared leather or other substance in the pendant-tubing, through which the winding-stem passes.

Padparadscha, padmaradschah - The first version is the German one and it is especially applied to the synthetic orange or pinkish orange corundums. According to gemologist G. F. Herbert-Smith, it was adapted from the Singhalese word for lotus-colored "padmara-gaya," hence the second version. Also spelled padparajam. In natural stones this controversial name is applied to tangerine-colored sapphires, highly prized in the Orient. The true padparadscha, as opposed to some Tanzanian stones which have been so labeled, has a touch of pink in its orange, which is not evident in the African stones.

pagoda stone, pagodite - There are two definitions for this, the commonest being that it is a synonym for agalmatolite. According to one authority, it is a Chinese limestone containing fossils which, in section, can be likened to outlines of pagodas.

painted diamond - A diamond that has been coated, often on girdle or pavilion, with a superficial film to neutralize slight off-color. An early method was application of an indelible pencil to culet area. In 1950's, a nearly invisible coating technique was developed that could only be removed mechanically or with hot acid. Such stones appear greenish or greyish in comparison with normal master-color diamonds. Federal Trade Commission
rules forbid the sale of any stone that has been artificially colored without disclosure.

pair-case - A watch case in which an inner case contains the movement, with an easily detachable outer case, usually removed for winding with a key; this type case has been largely obsolete since establishment of stem-winding, but occasionally is seen on stem-wound watches still in use.

palladium - A white metallic element of the platinum group, used in dentistry, jewelry, and chemical and electrical equipment. Specific gravity 11.96; melting point 1554 deg. C.; chemical symbol Pd. It differs from others of the group in that it is attacked readily by nitric acid and by hot concentrated sulphuric acid. Unalloyed it is soft and so malleable that it may be beaten into leaf for decorative purposes. It is hardened by the addition of small amounts of other metals, ruthenium and nickel being the most efficient. It forms useful alloys with many metals. When added in small amounts to gold, the yellow color fades quickly, and alloys containing 15 per cent palladium are quite white. Gold-palladium alloys, with or or without other elements, are used in jewelry as "white gold," as solders in the manufacture of platinum jewelry, as substitutes for platinum in chemical operations, in dentistry, in rayon spinnerets, etc. The alloy containing 95 parts palladium, 2 to 4 parts ruthenium, and the remainder rhodium is suitable for jewelry, it has the look of platinum but is only half as heavy. See also PLATINUM GROUP.

pallet - Part of an escapement, usually a detainer against which a tooth of the escape wheel rests during the condition called "lock." Another function of most pallets is as the part through which an escape wheel tooth imparts power, through a lever, to the balance. Pallets are usually made of a hard stone, such as sapphire; but in cheap watches, and most clocks, of steel. In chronometer escapements there is one pallet solely for locking the escape wheel, another for unlocking the detent, and a third pallet for receiving impulse only. See ESCAPEMENT; PALLETS.

pallet arbor - The pivoted arbor on which is mounted the yoke of the pallets in a watch or clock. See PALLET; PALLETS.

pallets - A term denoting, in lever escapement, an assembly of three parts including a receiving pallet, a discharging or let-off pallet, and the metal yoke in which both pallets are set and which is mounted on a pivoted arbor which also carries the fork-lever, all of these parts fastened rigidly together and moving in unison in the action of the escapement. In most clocks, "pallets" means one piece, of steel, comprising the receiving and let-off pallets and the yoke connecting them.

pallet stones - Pallets for lever escapements, made of hard stone, a pair comprising an "R" stone (receiving); and an "L" stone (let-off). See PALLET; PALLETS.

pallions - Pieces into which solders are cut for convenience in applying to work.

pampel, pampille - A fancy facet cut stone of a drop shape and circular or almost circular cross section.

Panama pearl - Pearls fished off Panama. See LA PAZ PEARLS.

Panama shell - A green-edged variety of Margaritifera shell found in the Gulf of California. Gemologist G. F. Herbert-Smith says this area is noted for the black pearls it produces.

paneled - Decorated with small surfaces framed either by moldings, engraving or by the outline of the piece itself.

pantograph - Principle used in engraving machines, an arrangement of levers through which a tool is guided by a metal pattern so as to copy the pattern on the work, on enlarged, reduced, or similar scale. See ENGRAVING MACHINE.

paper-chronograph - An instrument for recording time, comprising clock-work which rotates a cylinder carrying a sheet of paper on which a pen marks instants of time, the pen operated by an electric circuit closed by a key or switch. This term is used to differentiate the instrument from a chronograph watch. See CHRONOGRAPH.

Paphos diamond - Misnomer for quartz.

Parachoc - Trade name for a jeweled shock-protecting device for balances.

parachute - Horology. A shock-proofing device, invented by A. L. Breguet ca. 1800, for protecting watch balance pivots and jewels from damage from violent blows or falls; essentially it is the mounting of an endstone setting on a steel spring which yields momentarily during abnormal pressure of a pivot-end on the endstone, as when a watch falls or is struck a blow.

paraffin treatment - Among the uses for paraffin in the preparation of gemstones are these: to improve the color and polish of turquoise; sometimes with blue added, to disguise whitish, rough areas of cut lapis; to hide fractures in the final preparation of jade and dyed jadeite; and as a bath for stones produced by commercial tumbling concerns. Now superseded by plastics as a rule.

paragon pearl - Round pearls of exceptional size, monster-pearls.

parallel caliper - A type of balance-truing caliper in which the axes of the pivot-holding tips coincide with the axis of the staff of the balance being trued, at any and all degrees of opening of the caliper.

Paris pearl - Misnomer for an imitation pearl, made with the extract of fish scales.

paronigar - An Indian workman who strings beads.

parti-colored stones - Gems showing zones of different color, a phenomenon often seen in tourmalines where they may be bands of pink and green; and sometimes in corundums which are occasionally red and blue, or yellow and blue.

parting -1. Gemology. A property of minerals resembling cleavage, but unlike the latter in that it will not take place in any plane, but only in certain definite parallel planes where a disturbance has taken place in the crystal lattice which amounts to a twinning. It is important in a few gem minerals, notably corundum, pyroxene and sphene. See FALSE CLEAVAGE. 2. Metallurgy. A detail of the recovery of precious metals from scrap or wastes, comprising chemical processes for separating the various metals originally together in the mass.

parure - A set of matching pieces of jewelry, such as a bracelet, brooch, rings, earrings, necklace, etc.

passing hollow - A notch cut out of edge of the roller table in a lever escapement, to allow the guardpoint to pass from one side to the other during the unlocking and impulse functions of the fork-and-roller action. See LEVER ESCAPEMENT; FORK ACTION.

passing spring - The thin spring, usually of gold, fastened to a chronometer detent, its free end projecting slightly beyond the horn, to receive the unlocking pallet during the impulse-vibration of balance and unlock the escapement; during the next or "dumb" vibration, the unlocking pallet brushes the spring out of its way and passes without further effect, hence "passing" spring. See CHRONOMETER ESCAPEMENT; DETENT.

Passau pearl - A fresh water pearl from central Europe; Passau was the center of the industry.

paste - Glass used for cheap, inferior gem imitations. It comes from pasta, Italian for food, in allusion to its soft plastic nature. See STRASS.

patch-eye, pad eye - An item of jewelry findings, a suspension ring with an attached plate of metal for soldering it to a piece of jewelry.

patina - (pat-teen'a) A green film formed on copper and bronze, usually indicative of age, though easily hastened artificially. By extension it is used for any surface alteration of various materials from long exposure.

pattern - 1. An object worthy of imitation. In jewelry, a wax reproduction of an original to be consumed in casting its duplicate. 2. An original wax model to be used directly in producing a casting.

pave, pavement, paviment - (pah-vay', pahv'mawn', pahv'i-mawn) A type of setting in which a number of small stones are set as closely together as possible.

pavilion - The lower side of a cut diamond. In a round brilliant, the pavilion depth, from girdle to culet, ideally is 43.1% of the diameter of the girdle.

pavilion facets - 1. Four of the large facets that extend from girdle to culet of a brilliant cut diamond, alternating with the four similarly-shaped bottom-corner or quoin facets. Also termed bottom main facets. All eight of these facets are collectively called pavilion facets in the U.S., and lower main facets in Scandinavian Diamond Nomenclature. 2. All facets of any cut stone that are below the girdle, as contrasted with the crown facets that are above the girdle.

pawl - A pivoted catch-piece, or click, with a point to catch and hold the teeth of a ratchet wheel, as in the winding mechanism of timepieces.

peacock stone - Malachite cut so that its bands form an eye, worn in Italy to protect the wearer from the spell of the Evil Eye. The name is in reference to its resemblance to the markings in the peacock's tail feathers.

pear-drop, pear-eye pearls - Drop-shaped pearls suitable for use as pendants or earrings.

pearl - A nacreous, calcareous concretion formed within the body area of some mollusks. It is composed of concentric layers of calcium carbonate with organic material (conchiolin) serving as the binding medium which holds the tiny carbonate crystals together (nacre). The thin layers of extremely minute crystals formed by some mollusks result in the formation of pearls with a beautiful iridescent sheen (orient) on gem pearls. Many mollusks form pearls; only a few are valuable. They may be free within the mantle or they may be attached to one of the shells. The exact cause of their formation is not known, but it is presumed to be due to an irritation by some foreign body which has gotten into the mollusk, perhaps a grain of sand, perhaps a parasite. By Federal Trade Commission rule, it is an unfair trade practice to use the word "pearl" to describe a cultured pearl, unless the word "pearl" is preceded by "cultured," "cultivated" or a word of like meaning, or to describe an imitation pearl unless the word "pearl" is preceded by "imitation," "simulated" or a word of like meaning—to indicate clearly that the product is not a pearl. See ABALONE PEARL; BOMBAY PEARL; BUTTON PEARL; BALL PEARL; BAROQUE PEARL; BELL PEARL; BLUE PEARL; BIRD'S EYE PEARL; BLISTER PEARL; CHINA PEARL; CLAM PEARL; CONCH PEARL; CROP PEARL; CULTURED PEARL; CYST PEARL; DROP PEARL; DUST PEARL; FRESH WATER PEARL; IMITATION PEARL; SEED PEARL.

pearl corundum - A variety of corundum with a bronzy, iridescent luster.

pearl doctor - One who scrapes away the outer layers of poor pearls in the hope of getting a better colored or more perfectly shaped earlier layer. See PEELING.

pearl drill - A special form of drill, used in a pump-drill stock or flexible shaft tool, for producing in a single operation the seat (bottom and bezel) for setting a hemispherical flat-bottomed or half-pearl. See PUMP DRILL.

pearl drop - An item of jewelry findings, comprising a baroque pearl or an imitation pearl with ring attached for suspending on a piece of jewelry.

pearl-eye - A perfectly round pearl.

pearl garnet - A dark brown variety of angradite.

pearl gauge - A scale showing the weights of spherical pearls for an increasing series of diameters.

pearl grain - The unit of weight by which pearls are sold, it is equal to % ct.

pearling - Horology. Decorative finish for parts of watches, clocks and fine tools; comprising a series of spots with circularly grained surface, partly overlapping each other; produced by rotation of a flat-end lap of wood or similar material on the surface of work over which has been spread a mixture of abrasive powder and oil; also called "spotting." See DAMASKEENING. 2. Gemology. The business of pearl fishing.

pearlite - PERLITE.

pearl luster - The brightness of the reflection on the rounded surface of a natural or cultured pearl.

pearl mussel - The fresh water pearl-forming mollusk of the genus Unionida.

pearloscope - A binocular microscope with illuminator and an apparatus like that of the endoscope for the examination in a mirror the surface walls of the boring.

pearl oyster - The popular name for the pearl-producing mollusks of the genus Margaritifera, the principal salt water pearl producer.

pearl sac - The tissue that forms about the irritating agent and secretes the nacre that for the pearl.

pearl shooting - A term for the artificial color: of pearls.

pearl-slug eye - An item of jewelry findings straight short wire with ring at one end; inserting through hole in pearl for suspend it.

Pecos diamonds - Misnomer for quartz crystals from the Pecos River of New Mexico a Texas.

pectolite - Calcium sodium silicate, one of the zeolite minerals which sometimes occurs compact masses of long white needles. Usually too friable for any use, it occurs in Alaska tough masses which have been carved by the natives into ornaments and tools. Also called pectolite-jade, erroneously.

peeler - A pearl of inferior surface appearance but one which, it is thought, might be improved by the removal of a few layers.

peeling - The process of removing layers from the surface of a pearl in the hope that a better quality will be found in the interior. See PEARL DOCTOR.

peening - Hammering metal with a round-faced hammer, usually to stretch one side of an object, as in straightening a bent metal rod or plate.

Pegmatite - (peg"mah-tite') A coarsely crystallized residual magma mass, usually in the form of a dike or a lens, resulting from the slow solidification of a deep-seated igneous intrusive, such as often results, for example, in the formation of granite. (Some authorities restrict the meaning to a particular type of quartz-feldspar intergrowth). With the concentration of volatiles which make the crystallizing magma more fluid, with the resultant larger crystals, there is a concentration of rare elements, such as beryllium, boron and fluorine, which are fixed in the form of the uncommon minerals, beryl, tourmaline and topaz, i.e., many of the gem minerals.

peg setting - A setting consisting of a peg, often set into a metal hemisphere, which fits into a hole drilled part way into a pearl. The pearl is fastened with pearl cement or epoxy cement.

pegwood - See ORANGEWOOD.

peliom - CORDIERITE.

pendant - 1. Jewelry. A hanging ornament or decoration, usually suspended on a chain. 2. Horology. The part of a-watch case to which the bow is fastened, for holding the watch to its chain; in stem-winding watches the winding stem passes through the pendant, which is capped by the winding crown.

pendant-bow pliers - A special form of pliers for opening or closing bows of watch cases.

pendant-set - Classification of stem-winding watches which are set to time by pulling on the winding crown, which disengages stem from winding mechanism and engages it with setting mechanism; this term differentiates from "lever-set" watches, which are set by pulling out a lever from under the glass bezel. See NEGATIVE SETTING; POSITIVE SETTING.

pendant sleeve - A split steel collar screwed inside the pendant of a watch case, for holding stem in positions for winding, or setting, the watch in negative-set watches. See NEGATIVE SETTING.

pendeloque cut, pear cut - (pahn'dah-loke) A variation of the brilliant cut, with pear-shaped girdle and usually 58 facets.

pendulette - 1. A false, short pendulum in a clock observed through a curved aperture in the dial. 2. A very large watch.

pendulum spring - A short, thin steel spring at the upper end of a pendulum rod, fastened to the suspension bracket of a clock, its flexibility allowing the pendulum to swing.

pendulum watch - Watches in vogue during the late 17th and early 18th Centuries, having on an arm of the balance wheel a representation of a pendulum bob, with its motion visible through an opening in the balance cock, or occasionally contrived to show this through an opening in the dial.

Pennsylvania diamond - Misnomer for PYR1TE.

pennyweight - A unit of Troy weight, used for weighing precious metals. The pennyweight contains 24 grains and is one-twentieth of an ounce. Abbreviated "dwt"; occasionally, "pwt." Inexpensive gems, like amethyst and citrine, are sometimes sold by the pennyweight, which equals 7.78 carats. See TROY WEIGHT.

pentagon - A fancy diamond shape in general like a square with one edge replaced by two sloping sides.

pentagon facet - A British term for the pavilion and quoin facets.

perchlorethylene - A non-explosive colorless, volatile liquid used as a degreaser in cleaning fluids.

percussion center - Point in a pendulum where its mass exerts greatest force; usually situated slightly above center of the bob. See BOB; PENDULUM.

perfect - Diamonds. It is an unfair trade practice to use the word perfect, or any other word of similar import, as descriptive of any diamond which discloses flaws, cracks, carbon spots, clouds, or other blemishes or imperfections of any sort when examined in normal daylight, or its equivalent, by a trained eye under a ten-power, corrected diamond eye loupe or other equal modifier. -U.S. Federal Trade Commission. The FTC disapproves of the use of perfect or similar term for a diamond of inferior color or make. The American Gem Society forbids its members to use the word perfect in describing or advertising diamonds. See FLAWLESS.

perfection colors - The finest color for the variety of gem in question.

peridine - Name proposed for the Brazilian, Arizona or African amethyst which has been turned green, instead of citrine, by heat. It is a characteristic of some amethysts to change in this way. The name combines peridot and citrine to make a euphonius new name which is self-explanatory.

peridot - The jewelers' name for the gem variety of CHRYSOLITE. It is a desirable word because there seems to be no confusion in anyone's mind about what gem is meant. See also FORSTERITE; HAWAII! E: OLIVINE.

peridotite - A dark-colored rock, composed principally of olivine and pyroxene. Kimberlite, the matrix of the diamonds in the pipe mines, is a peridotite.

perigem - Trade name for light yellow synthetic spinel.

peristerite - A white to reddish albite with bluish schiller colors. Like a moonstone, but less translucent.

perlite - The correct version of pearlite. A slightly altered variety of obsidian, named originally in reference to its tendency to break down into rounded concentric structures. By extension, it has come to mean a gray obsidian. Pebbles of this material from New Mexico and elsewhere, have been cut to make interesting looking, lustrous stones. See PITCHSTONE.

permanent magnet - A substance that can retain its magnetic properties long after its magnetic exciting influence has been removed.

permeability - Magnetism. The ability of a substance to absorb magnetism to a high degree. See MUMETAL.

Persian turquoise - Like other locality modifications, this one has come to have no reference to the true source, but means, rather the finest quality of turquoise, as it is generally used.

perspex - A polymerized acrylic ester plastic a specific gravity of 1.18 and R.I. of 1.5C the British equivalent of Lucite.

Peruzzi cut - An old diamond cut attributed to the Venetian, Vincent Peruzzi, toward the end of the 17th Century, with 32 upper and 24 lower. This was an improvement the earlier MAZARIN CUT.

petal pearls - Distorted, flattened pearls.

petalite - An uncommon, usually colorless lithium aluminum silicate, found in matites and cutable into clear, but very refractive-indexed stones. Their hardness to 6 1/2, density about 2.40, and the R.I. ; about 1.51. Stones have been cut from Brazilian and Australian material.

Petoskey stones - Fossil coral, commonly found in the shape of waterworn limestone pebbles on the shores of Lake Michigan at Petoskey, Mich.

petrosilex - HORNSTONE.

petrographic microscope - (pet-ro-graff-ik) A microscope especially adapted, as the name implies, for the study of rocks. It is a far more complicated instrument than the ordinary biological microscope, having a rotating stage, polarizing elements, a supplementary lens in the tube and slits for the insertion of wedges.

petuntse - Also called china stone; a fusible silicate of aluminum; a component of porcelain.

phantom - The trace of an earlier growth stage included within a crystal. Quartz crystals sometimes show numerous phantoms which have formed when a foreign substance lightly coats a crystal plane, following which additional silica was deposited, including the foreign material in a definite band delineating a transient surface. In a sense, the color banding commonly observed in sapphires can be considered a series of such phantoms.

phenakite - (fen'a-kite) Sometimes spelled phenacite. A rare beryllium mineral, beryllium silicate. Sp. gr. 3, refractive index, 1.66, hardness, 71/2-8. Found in but few localities, gemmy only in Brazil and Russia. Usually colorless or slightly yellow; never rose-red, brown or yellow. An uncommon but attractive gem, of moderate brilliance, of interest only to collectors.

phenomena - A term which has been taken by gemologists to describe any of the abnormalities of gemstones, like asterism, chatoyancy, adularescence, etc.

Phillips curves - Term sometimes applied to terminal curves for balance springs, in recognition of the investigations of Edouard Phillips in the theory of isochronism.

philosopher's stone - A magic substance, sought by alchemists as late as 1750, which could transform base metal by "projection" into gold. Wrapped in wax, the stone was "projected" into a crucible containing molten lead, tin, copper or other metal. "True" alchemists sought to transmute man from the limited world of the senses into a superior state.

phosphor bronze - A metal alloy of 80% copper, 10% tin, 9% antimony and 1% phosphorous, non-corrosive, and in some cases used as bearings.

phosphorescence - The property of continuing to emit light after the exciting agent has been removed, such as in some paints used on clock or watch dials. Some diamonds and other stones glow in the dark after exposure to ultraviolet rays, x-rays, or visible light. See FLUORESCENCE.

phosphoroscope - An instrument with slits and shutters designed to permit vision of a gem within it only when the light source is obscured, and hence permitting the recognition of phosphorescence of even a very short duration.

photometer - An instrument developed in Germany to measure textile colors, subsequently adapted for diamond color grading.

pickle - A mixture of about nine parts water and one part sulphuric acid, used by jewelers for cleaning gold and silver work after soldering. Pickle solutions are preferably used hot in copper pans or heat-resistant glass beakers. See SPAREX.

pickle pan - Copper dish used to heat pickle for removal of metal oxides. See PICKLE.

picotite - A black spinel, spoken of as one of the possiblities for the black inclusions in diamond.

piedmontite - A manganese epidote of a brown red color. Cut cabochon but probably of little or no gem interest. Also spelled piemontite. From San Marcello, Val d'Aosta, Piedmont, Italy, and elsewhere.

piercing - Jewelry. A term used to indicate the cutting of an opening or design in metal, using the jewelers' saw.

piezo-electric effect - An effect of alternate expansion and contraction produced in certain crystals, for example in quartz, by an electric current, giving oscillations of high frequency and periodic uniformity, taken advantage of in construction of certain timekeeping instruments and radio oscillators. See QUARTZ CRYSTAL. Tourmaline exhibits this phenomenon and thus may be distinguished from andalusite.

pigeon blood agate - A bright red agate found on the desert south of Cisco, Utah, really a carnelian, but some specimens are banded with white agate. An undesirable local name.

pigeon blood ruby - The classic name for the finest color of ruby, a slightly bluish red. Becoming paler, it grades imperceptibly into pink sapphire.

pig-toe clam or mussel - A thick-shelled lower Mississippi River fresh-water mussel sought for the cutting of the nuclei for cultured pearls.

pile-treated stones - Diamonds colored by bombardment by fast neutrons in an atomic pile, a method used with mounting commercial success after the early Nineteen Fifties. Colors include red-brown, canary, gold, yellow-green, tourmaline green, blue-green and near-black. All treated and heated diamonds develop certain absorption lines in their spectra that permit experts to distinguish them from untreated diamonds.

pillar - 1. Horol. One of the posts or columns that stand between plates of the framework of a watch or clock movement, to hold them apart; part of the structure that supports bearings for the-moving parts. 2. The upright posts that support the teeth of a cylinder escape wheel and connect them with the face of the wheel.

pillar file - A narrow flat-faced file, so called because originally used to file faces on ornamental pillars of watches after they were riveted into the lower plate.

pillar nut - Metal disc with slots or faces, drilled and tapped to screw on threaded top of clock movement pillar, for holding plates together. See PILLAR.

pillar plate - The lower plate of a watch or clock, into which the pillars are rigidly fastened.

pillar screw - The screw that fastens the upper plate of a timepiece to a pillar.

pinacoid - A crystal form of all systems but the isometric, consisting of two parallel faces. The crystal axes run parallel to the intersections of the pinacoidal faces.

pin-back - An item of jewelry findings; an assembled joint, pin and catch on a metal plate ready to be attached to any piece of jewelry for making up a brooch.

pin brass - A brass composed of about 60 per cent copper and 40 per cent zinc, used formerly for making jewelry pins; now frequently used as alloy in making silver solders.

pinchbeck - A reddish-yellow brass largely used for imitating gold; a common formula is 88.8 per cent copper, 11.2 per cent zinc. Named for its inventor, Christopher Pinchbeck (1670-1732), a London watchmaker.

Pinctada margaritifera - 1. Pearl-bearing mollusk of Persian Gulf, Burma, Ryuku Islands and Gulf of California. 2. P. martensii. Of Japan. 3. P. maxima. Of South Seas and Burma.

pin fire opal - A variety of precious opal in which the color flashes are in the form of very small spots. It is a less valuable form of opal than the larger spotted harlequin opal.

pinion - A member of a train of gears; specifically, a gear-wheel of relatively small diameter, hence usually without wheel-spokes, but comprising only the teeth called "leaves" and the core or body left by cutting the leaves out of a solid piece of material. See GEARING; LANTERN PINION.

pinion gauge - A spring caliper of small size adjustable by a screw and nut for gauging lengths and diameters of pinions, etc. during turning operations.

pinion stake - A narrow block of steel or brass with about ten holes of graduated sizes for supporting pinions while staking on wheels.

pinion wire - Steel wire drawn in form of a cross-section of the body and leaves of a watch or clock pinion; sold by watch material dealers in lengths of one foot; pieces are cut from the wire then turned and finished to make up pinions for repair-jobs.

pinite - A variety of serpentine particularly one derived from the alteration of certain other minerals. Some authorities consider it related to muscovite mica. See AGALMATOHTE.

pinking - Term for the heat treatment of topaz by which golden brown gems are turned pink.

pink moonstone - Pink SCAPOLITE cat's-eyes found associated with the ruby at Mogok, Burma.

pink sapphire - Pale red stones, grading insensibly into rubies, but no hard and fast color line can be drawn and it is not unlikely that stones from Montana are called pink sapphire while paler Ceylonese stones get by as rubies.

pinna pearls - Reddish, formerly highly valued pearls of the Pinna mussel. Their structure is far coarser than that of the MARGARITIFERA pearls.

pinning points - The location of places on inner and outer terminals of hairsprings where these are pinned respectively to the collet and to the stud. Changing the relation between these two points is one of the controls over the rates of a watch in different positions.

pin-pallet escapement - Clock escapement mostly seen on mantel clocks of French manufacture with the escapement visible against the background of the clock dial; more important for attractive appearance than for horological merit. The pallets are usually of agate or garnet, shaped like the roller jewel of a lever escapement, set horizontally in the pallet yoke; escape wheel teeth with flat radial faces to provide for locking and lifting on the pallet pins. A disadvantage is that oil tends to work away from the surfaces where needed.

pin-pallet lever escapement - The escapement mostly used in alarm clocks and nonjeweled watches. While not adapted for fine timekeeping, it has advantages in economy of manufacturing costs, and is sturdy and reliable in service.

pin-pusher - A cylindrical steel punch mounted in a handle, for removing hinge pins from joints of watch cases, lockets, etc.

pinstem - An item of jewelry findings, mountings for various stones, etc., with attached pin, for making up tie pins.

pintong - A tool used by jewelers for holding pin tongues, while shortening and sharpening them. It has two spring jaws, closed by a ring sliding on the outsides of the jaws. It is quick-acting, but not as tight-gripping as a pinvise.


pin-tongue - An item of jewelry findings, comprising a pin on a base with a hole in it to hold the joint-pin which is part of the hinge. Pin tongues are used on brooches, bar pins, etc., to fasten them to the clothing of the wearer. See PIN-VISE.

pin-vise - A small hand-held tube with a spring collet or chuck at either end in which pins, stems wire, etc. may be held for manipulation.

pin wheel - In some striking clocks, a wheel with pins set perpendicularly to the face of the wheel, to operate the tail of a lever for lifting the hammer.

pin-wheel escapement - Clock escapement invented by Jean A. LePaute of Paris in 1753. Instead of teeth the escape wheel has pins standing out horizontally at right-angles to the face of the wheel; these fall on pallets with concentric circular locking faces, set one above the other, with lifting faces nearly opposite each other. This escapement was used in many French regulators and tower clocks; but its popularity declined largely due to difficulty in keeping it oiled.

pipe - Horology. 1. A tubular extension on a wheel, to allow rotation on a bearing; for example the hour-wheel pipe in a timepiece, which runs on the cannon pinion as its bearing. 2. A tubular projection, for attaching one part frictionally to another to allow movement together; example, the pipe of a seconds-hand, which fastens the hand to the extended fourth-pinion pivot.

pipeclay - A white powdered earth, used for polishing non-ferrous metals.

pipe opal - Elongated masses of precious opal, replacing a cigar-shaped fossil (Belemnites, White Cliffs, N.S.W.) or filling in a similarly shaped cavity in the rocks (Queensland).

pipi pearls - Small 4 to 12 grain milk-white pearls from the shallower waters near Tahiti

pique - (pee-kay1) From the French piquer, to pick. 1. Diamond clarity grade. Originally, just touched with slight imperfections, visible under a loupe to a trained eye. b. Use of "P" or "Pique" is recommended by Scandinavian Diamond Nomenclature, 1970, instead of "I" or "Imperfect," with sub-grades P! P2 and P3 for stones weighing 0.50 ct. or more. 2. Horology. Kind of ornamental work on shagreen or tortoise-shell covered cases of antique watches, etc., consisting of small gold or silver rivets set in designs, the rivet heads showing on the outside of the case-covering.

pirouette - A device tor multiplying the turns of motion of a watch balance by gearing, invented by Huyghens in his experiments to apply the hairspring; of historical importance, but technically faulty.

pit amber - Mined amber.

Pitch - A black substance obtained from the distillation of coal tar. When mixed with resin, plaster of Paris and tallow it is known as Burgundy pitch and used to hold work for chasing and repousse.

pitch circle - A circle concentric with the circumference of a gear wheel, used in designing gearing, cutting the teeth at such a distance from their points as to touch the corresponding circle of the pinion that works with the wheel, and having with that circle a common velocity, as in a rolling contact. Calculations of relative numbers of turns of wheels and pinions are based on the measurements of the pitch circles, or their diameters or radii.

pitch coal - JET.

pitch diameter - The diameter of the pitch circle of a gear wheel or pinion. See PITCH CIRCLE.

pitching - Adjusting the depth of engagement of wheels and pinions.

pitching tool - A depthing tool, based on the principle of the proportional compass, for determining primitive diameter of a wheel to match a pinion, or of a pinion to match a wheel, without calculations.

pitch opal - Brown, semi-opal with a greasy luster.

pith - Cellular substance from interior of certain plant stems, such as elder pith, used for cleaning purposes in horology.

pits - 1. Cavities formed in steel surfaces by the corrosive action of rust. 2. Spots worn in endstones by grit on end of pivots.

pivot - The portion at end of an arbor, formed to run in a hole or bearing, to allow rotary motion of the arbor; or a similar part at the fulcrum of a lever to allow angular motion; or a fixed pin on which a part turns on a hole or pipe in the part. See CONICAL PIVOT; SHOULDER PIVOT.

pivot broach - Very small broaches in graded sets, both for cutting and polishing, made for finishing to size and polishing drilled holes for pivot bearings.

pivot-detent, pivoted detent - In the chronometer escapement, a detent with a pivoted arbor on which the detent turns during unlocking of escapement, the detent being then returned to its banking by a spiral spring on a collet on the arbor. The other type detent is the spring-detent, a portion of which is a thin flat spring of steel, that performs the functions of the arbor and spiral spring of the pivot-detent. The pivot-detent is characteristic of Swiss and French chronometers; the spring-detent, of American and English chronometers.

pivot drills - Very small drills of standard flat form, sold in sets of sizes for drilling holes to hold steel plugs for repivoting operation in watch repairing. See PIVOTING.

pivot gauge - A gauge of the fixed type for measuring diameters of pivots and small arbors, consisting of two bars of thin steel fastened to end-pieces so that there is a tapering slot between the bars, which are graduated to indicate a diameter, at any point where a piece of work comes to a stop when moved along in the slot.

pivoting - A trade term designating the operation of replacing a broken pivot by drilling a hole concentrically in the arbor, fitting in a steel plug, and turning a new pivot on the outer end of the plug. A term more definite than "pivoting" is re-pivoting, which is increasingly being used.

pivot lathe - Special dead-center lathe, made to be driven with hand-bow, for quickly making slight alterations or finishing pivots, without removing staff or arbor from wheel. Used especially by watch adjusters.

pivot polisher - A small traverse-spindle grinder, used as an attachment to a watchmaker's lathe of the American type, with a pulley for driving it from the bench countershaft, with a taper on spindle-end to hold circular laps for grinding and polishing pivots and other lathe work of small diameter. The spindle runs in bearings in a yoke mounted on an adjustable base bolted to the lathe bed. The laps are of metal, bone, etc., used with abrasive powders in oil.

pivoted suspension - A pendulum without a suspension spring and swinging with its arbor in pivot holes as in very short pendulums.

placer - (plass'er) Alluvial deposit of secondary material, in which ores or gems are found and recovered by such methods as panning, hydraulic washing, dredging, etc. See ALLUVIAL.

plagioclase - (plaj'ee-o-klase) The triclinic group of feldspars: albite, oligoclase, labradorite (bytownite, anorthosite).

plain balance - A watch balance, as used now in watches with cylinder escapement (and used in all watches prior to introduction of bimetallic compensation balance), in which arms and rim are of one piece of metal, without screws in rim.

plain cut - A form without facets, cabochon, for example.

plane of symmetry - In crystallography, the planes of symmetry are important for the classification of crystals; their system and their class. They can best be visualized as planes along which a crystal could be divided into identical halves.

plane polarized light - Light which has passed through a polarizing medium, such as a nicol prism or a sheet of Polaroid, and as a result all of its vibrations are in parallel planes. Such light is useful for the observation of pleochroism, etc.

planishing - Treatment of soft metals by hammering, striking blows that cover the area of the work; for some operations in forming pieces of work, or for condensing and improving the grain of the metal, like planishing cast brass preparatory to using it for making parts of clocks or watches.

plasma - Dark green jasper, with, perhaps, white or yellowish spots. Red spots would make it bloodstone.

plasma furnace - Verneuil-type device capable of producing from ionized gas intense heat which can be used for the fusion of gem materials. More costly than the normal Verneuil burner, it finds little use in gemstone synthesis.

plastic lubricant - A common, broad term applied to a compound of lubricants, some silicone-based, and mixed with the last rinse in an ultrasonic cleaning machine wherein the assembled movement is "lubricated" while being rinsed after cleansing cycles have been completed.

plastics - Synthetic resins of many types; celluloid, Bakelite, Catalan, Lucite, etc., can all be included under this general term.

plate cut - A gem cut consisting of a thin plate with two large parallel sides, possibly bounded on one or both surfaces by some narrow steps. A common type of cut for opaque ring stones such as lapis, turquoise, opal doublets, onyx, chalcedony, agate, etc.

plate powder - Polishing powder for silver, much used in England, an old formula being: prepared chalk or whitening, 2 parts; oxide of tin, 1 part; calcined hartshorn, 1 part, well powdered and mixed together.

plates - In watches and clocks, the flat metal parts of the framework of movements, comprising the lower or pillar plate and upper plate, pierced with drilled or jeweled holes that form bearings for the pivots of the acting parts. 2. The brass discs in a lantern pinion, that support the ends of the rounds that act as pinion leaves. See BAR MOVEMENT; FULL PLATE; LANTERN PINION; THREE-QUARTER PLATE.

platform escapement - An interchangeable escapement situated on a removable plate such as used on carriage clocks and often motivated by a contrate wheel at right angles and visible through a window atop the clock.

platinize - To coat or finish with a layer of platinum. Usually accomplished by electro-deposition or by the reduction of platinum salts.

platinum - A white metallic element, the most important member of the platinum group; named platina, meaning "silver of little value," in 1735 by Spanish explorers of Colombia who didn't know what to do with it. In 1920, 65% of the platinum used in America went into jewelry, but in 1972 the figure was 2%; industrial demand had priced in out of the jewelry market. With the soaring cost of gold in the mid-1970's platinum began to regain its lost glory as the metal of choice for diamond jewelry. Quality marking of platinum in the U.S. is controlled by Commercial Standard 66-38. In Great Britain, under 1975 law, objects must be 95% platinum to receive the platinum hallmark. Specific gravity 21.4; melting point 1773.5° C., chemical symbol Pt. In the pure form it is soft and malleable. Hardness is noticeably affected by rolling and heat treating, also by the presence of impurities even in small amounts. The alloys containing 10 per cent iridium or 5 per cent ruthenium possess hardness and working qualities highly desirable in jewelry making, and are known as "hard platinum." See also PLATINUM GROUP.

platinum group - The six metallic elements, platinum, palladium, iridium, osmium, rhodium and ruthenium. They and their alloys have many applications in jewelry, dentistry, and the chemical and electrical industries. The six metals are generally found together in nature, platinum and palladium being the most abundant, and osmium, rhodium and ruthenium being the rarest. They have several characteristics in common: a silvery-white or tin-white color; rarity; unusual resistance to corrosion; high melting points; and certain chemical peculiarities, such as the formation of complex salts useful in electroplating and photography. With gold and silver they comprise the "noble" 01 "precious" metals.

play - Freedom allowed in fitting parts of timepieces to work together. See ENDSHAKE; SIDESHAKE.

play of color - The varying changeable colors seen in the opal, or the flash of color seen in the labradorite. Not to be confused with dispersion or "fire" seen in the diamond and zircon.

pleochroism - (plee"o-kro'ism) A difference in color seen in many (anisotropic) gems when they are viewed in different directions. Best observed with polarized light or through an instrument like a dichroscope. Dichroism is the same phenomenon when only two different colors are visible; gems of the hexagonal and tetragonal system are dichroic. Trichroism is used when a gem crystallizing in the orthorhombic, monoclinic or triclinic systems shows three colors.

pleonaste - An iron rich, black spinel.

Plexiglas - A trade name for a thermoplastic polymer of methyl methacrylate, a clear light plastic used for crystals, windows, boxes. See LUCITE;PERSPEX.

pliers - Two crossed metal limbs, hinged near their extremities, these forming jaws to grasp objects, bend or cut wire; round-nosed, long-nosed, cutting, curving, etc.

plug punches - Set of steel punches for adjusting height of cylinder plugs, comprising one flat-faced punch for replacing plugs, and an assortment of crank-shaped punches for altering heights in cylinder shell.

plugs - In a cylinder escapement, the steel bases on which the balance pivots are formed; the plugs are fitted friction-tight in the cylinder shell at each end. See CYLINDER ESCAPEMENT.

plumb gold - A gold alloy of the same fineness as marked, or perhaps with a small tolerance such as .003, instead of the half-karat or full-karat tolerances permitted by the National Stamping Act of 1906. Under the latter, for example, goods marked 14K (.5833) could assay 13'/4K (.5625); or, if soldered, the entire article including solder could assay as low as 13K (.5417). See KARAT GOLD; TOLERANCE.

plume agate - A variety of moss agate, characteristic of thunder-egg cores; the translucent agate (chalcedony) contains replacements, often colorful, of feathery growths which occupied part of the open gas cavity, before its filling by silica. The nature of the original crystals is uncertain, but now they create flowery effects in the translucent filling. Relatively little known away from Texas and Oregon, where they are much sought after, they are the prizes of many amateurs, costly but of little significance to the commercial trade.

plunger - A pendant in a repeating watch which is depressed to activate the striking.

plus curve - A term used by some watch adjusters, to designate a form of overcoil in a Breguet hair-spring that is more rigid (less flexible) than the adjacent portion of the body of the spring, so formed with the idea of making the short-arcs rate faster.

pneumatic clock - A clock in which the hands are moved by a ratchet operated by a piston moved at intervals by compressed air piped to the clocks of a system, from a central station. The most extensive use of this system was by the Popp-Resche Co. for many years in Paris; now superseded by electric clock systems.

pneumatic hammer - Reciprocating hammer used on a flexible shaft for setting of stones by hammering surrounding metal over stone edge. A reciprocating device, actuated by compressed air for producing an infinite variety of surface finishes. This device is known as an Air Scribe and comes equipped with carbide or diamond tips.

pocket chronometer - A pocket watch with chronometer escapement; differentiated from the marine chronometer, which is a larger timepiece for navigating ships, mounted in a wooden case in gimbal rings for keeping the movement level regardless of the motions of the ship.

point - In diamond weight, one-hundredth of a carat. For example, a diamond weighing 48 hundredths of a carat (0.48 ct.) is termed a 48-pointer. Also, for example, melee of 0.01 ct., 0,05 ct., 0.10 ct. is spoken of as being one point, five points, 10 points. One point equals two milligrams.

point agate - POINT CHALCEDONY.

point chalcedony - A white or gray chalcedony which is so flecked with tiny red spots of iron oxide that the whole surface assumes a uniform soft red color.

point cut - Uncut octachedral diamond with only its faces polished.

pointed-tooth escapement - Lever escapement of English type, with escape wheel teeth having angular instead of clubbed acting ends of teeth. See CLUB-TOOTH; LEVER ESCAPEMENT.

point of attachment - See PINNING POINTS.

poising - The art of equalizing the weight of a watch balance at all points around its circumference; very important for securing uniformity of time-keeping rates in different positions; comprising essentially the removal or addition of metal at any part of balance rim found to be too heavy or light in relation to other parts of the rim. Balance is supported by its pivots, for testing, on knife-edge jaws of a poising tool; balance will come to rest with heaviest part of rim downward. From that part, some weight is removed, by replacing a screw there with a lighter one; or by cutting some metal from the shoulder of a screw; or weight may be added to upper part of rim; these alterations are continued experimentally until the balance, when turned to any position at all on the poising tool, will stand still without turning; the balance is then "in poise." See DYNAMIC POISE; STATIC POISE.

poising tool - Instrument consisting of a base mounting two adjustable parallel knife-edges, for testing watch balances to tell whether "in poise;" or for testing during poising operations. Balance pivots rest on the knife-edges, free to roll sensitively to any inequality of weight around the balance rim. See POISING.

poising undercutters - Small hollow milling tools for removing metal from shoulder of a balance screw during operation of poising.

polariscope - An instrument that enables a gemologist to distinguish between materials that are singly refracting and those that are doubly refracting. A transparent doubly refractive material transmits two light rays; it is easily distinguished in the polariscope from those transparent materials that pass a single ray. When superposed Polaroid plates are arranged so that they permit no light to pass directly through, a doubly refractive stone inserted between them (e.g. emerald) will on rotation appear light in some positions and dark in others, while a singly refractive material (e.g., spinel or glass) remains dark.

polarizer - A nicol prism or Polaroid film-any thing which transmits only polarized light.

polarity - The distinction between the north and south poles of a magnet. In demagnetizing a watch, what is affected is to mix or confuse the polarities of the molecules within the steel parts, so that these neutralize each other, instead of being similar in all the molecules and "pulling together" to make each steel part a magnet with its polarity attracting and repelling the polarities of other steel parts, thus setting up uncontrollable forces in the watch mechanism that interfere with its normal action, and spoil accuracy of timekeeping. See DEMAGNETIZE; MAGNETIZATION.

Polaroid - Trade name for polarizing film which consists of innumerable tiny crystals of a quinine, iodine compound, all aligned parallel in a transparent plastic sheet. The quinine iodine compound is strongly dichroic, like deep green tourmaline, and it absorbs almost all of the light vibrating in one plane and permits only the passage of light vibrating at right angles to the absorbed direction. In this way, all transmitted light is polarized.

polish-block - For mixing and keeping ready for use various abrasives used by watchmakers, a set of metal plates, usually three, each enclosed in a circular wooden block, the blocks fitted superimposed on each other, removable to expose any of the abrasives for use; otherwise kept closed to protect abrasives from exposure to dust.

polishing - The final series of operations in the production of jewelry. After a piece is made it is smoothened progressively from filing to successively-finer emery paper or cloth to buffs, wheels made of wood, leather, cotton and lambs wool charged first with pumice and followed by tripoli and rouge. See BUFF; BURNISHER; THRUMS.

polishing broach - A tapered length of hardened steel of round cross-section, with its surface scored with fine scratches, used in a handle for polishing pivot holes after drilling them, or after broaching out drilled holes to size with a cutting broach. See BROACH

polka-dot agate - A locally applied name to a Madras, Ore., occurrence of a more or less colorless, translucent chalcedony which is stained with small circular dots of red, yellow and brown. It is said to occur in enormous quantities on Pony Creek.

pollucite - A rare caesium mineral, a hydrous caesium aluminum silicate found in pegmatites and formerly in demand as a source of caesium. It is colorless and has a very low index of refraction, about 1.52, H. 6Vz, sp. gr. 2.92, and has gem interest only for collectors. Recent discoveries in Connecticut, Australia and Sweden of larger, purer masses than any previously known have been responsible for the appearance of a few cut gems. Very pale pink stones have been cut from a Portland, Conn., locality. See POLLUX.

pollux - The original name for pollucite, later modified, in allusion to its invariable association at the original locality, Elba, with a lithium mineral which was given the name castor.

poly chroite - IOLITE.

polyethelene - A synthetic plastic used in watches as case gaskets.

polysynthetic twinning - Twinning many times repeated in parallel layers and evidenced by bands along a cleavage surface, such as in the plagioclase feldspars.

pomegranate ruby - East Indian misnomer for red spinel, which some believe possesses medicinal properties.

popo - A green jasper, highly prized in Guinea (Africa); perforated beads have been used as money.

poppet - The headstock or tailstock of a dead-center lathe. See LATHE.

poppy stone - An attractive orbicular jasper with curving red splotches found in Paradise Valley and Llagas Creek, Calif.

porcelainite, porcelain jasper - Hard, really metamorphosed masses of baked green and red clay, found above coal beds in some parts of the West, and due to a natural burning of the underlying coal bed. They are not true jasper.

porcelain opal - Milky white, opaque opal.

porphyry - An igneous rock which has a fine grained ground mass in which there are dotted isolated larger crystals. The famous Egyptian porphyry has a red ground mass with small, white feldspar crystals. See ADINOLE.

portrait stone - Thin diamond plates, sometimes shaped and faceted on the edges and used as the covering for a tiny miniature in a ring or brooch.

Portuguese cut - A modification of the brilliant cut, with two rows of rhomboidal and three of triangular facets on both crown and pavilion.

Posalux - Trade name of a diamond-faceting machine.

position adjusting – Also referred to as “adjusting to positions.” The art of making alterations to parts of a watch, to obtain the nearest possible uniformity of timekeeping in the different positions the watch may assume in use. See ADJUSTMENT; DIAL-DOWN; DIAL-UP; PENDANT-UP.

positive double refraction - A feature considered in the identification of minerals; in uniaxial minerals, a positive one has the extra-ordinary ray higher in index than the ordinary ray; in biaxial, beta is nearer to the lower index than it is to the higher.

positive setting - Type of mechanism for setting watch hands to time, wherein the power for operating the shifting lever comes directly from a pull on the crown, instead of from a spring in the mechanism within the watch movement. See NEGATIVE SETTING.

potassium - A metallic element, a salt of which, potassium cyanide, is largely used in the jewelry trades, in solutions for electroplating, for cleaning silver, for brightening tarnished parts in cleaning watches, for extracting gold from crushed rock in mining, etc.

potch - Australian term for common, colorless opal found associated with the precious opal.

potence - A cock which holds the bearing for the lower balance pivot of a full-plate watch. It is screwed to the bottom of the upper plate, opposite to the balance cock, and below an opening in the plate through which the balance staff extends.

potted - Horol. A module which has been immersed completely in an epoxy bath in order to solidify the unit permanently.

pounced - Ornamented by a series of minute indentations made by a fine punch. Often used as a relief to more elaborate decoration.

pound paper - Sheets of paper and envelopes boxed separately so the customer may purchase additional supplies as he needs them.

powder metallurgy - The alloying and forming of metal parts by combining finely divided metal powders by pressure and heat.

power cell - A simple electrical cell; a one-cell battery.

power reserve indicator - On chronometers and some railroad watches, the amount of the mainspring's remaining running time is indicated on a dialette through a differential connected to the barrel arbor or fuzee. See UP AND DOWN INDICATOR.

prase - A dull leek-green chalcedony; the name is from the Greek word for leek, and sometimes is also applied to crystallized quartz filled
with needles of actinolite which make it a similar green color.

prase malachite - Chalcedony filled with malachite, found in copper districts of the West.

prasopal - A translucent, nickel-stained, apple-green colored common opal from Frankenstein, Silesia, where it occurs with the chrysoprase.

precision clock - A well-regulated clock adjusted to overcome most natural errors of temperature, isochronism, pressure etc.

precious coral - Noble coral, corallium nobile or corallium rubrum, rose red and red in color, the only species generally used in jewelry, though there are many other varieties.

precious metal - Metals which are prized because of chemical and physical properties (notably resistance to corrosion, hardness, strength, and beauty) desirable in jewelry, coinage, and objects of art, and which are at the same time relatively rare or expensive. Gold, silver, and the six metals of the platinum group are usually thought of as constituting the precious metals. See also NOBLE METALS.

precious olivine - Peridot.

precious opal - Opal of the gem varieties, including that with the play of color and the fire opal. See BLACK OPAL; BOULDER OPAL; BIDELLIUM; CAT'S EYE OPAL; COMMON OPAL; FLOATING OPAL; FLASH FIRE OPAL; FIRE OPAL; GOLD OPAL; HARLEQUIN OPAL; MEXICAN OPAL; MILK OPAL.

precious schorl - Gem tourmaline.

precious serpentine - Rich, translucent oily green serpentine.

precious stones - One of the three traditional categories of natural gemstones, the most valuable, as distinguished from semi-precious and decorative. Diamond, ruby, emerald, sapphire and pearl have long been considered "precious," but, in accordance with their spiraling prices, alexandrite, black opal, cat's-eye, demantoid and jadeite have won elevation to the circle of the elect. Because there is no clear line of distinction, all authorities would abandon use of such terms, preferring to call them all gemstones. See SEMIPRECIOUS; DECORATIVE STONES.

precious topaz - Term commonly used for true topaz, to distinguish it from citrine quartz (topaz-quartz).

precious tourmaline - The light-colored varieties of that mineral, there are many non-gem (black and brown) varieties.

Precium - Brand name for a palladium-silver alloy developed by Handy & Harman, New York; described as having a precious metal content of more than 87%, heavy weight, antique white color, and tarnish-resistance.

prehnite - (pray'nite) A pale green to white calcium aluminum silicate with water. It is a common associate of the zeolites, occurring in pale green solid crusts in trap rocks, and is sometimes cut cabochon, for it is never more than translucent, by collectors for use as a gem stone. Paterson, N.J., is a notable locality. Hardness, 6-7, sp. gr. 2.8-3. Refractive index, 1.63. Also known as Cape Chrysolite, Cape Emerald. See CHLORASTROLITE; CHRYSOLITE.

premier oillies - Typical stones of the Premier mine, with a bluish fluorescence visible even in daylight, which gives them a wonderful opalescent appearance, but the true body color may be distinctly yellow and the quality lower than stones which have none of the bluish fluorescence. Not all fluorescent diamonds can be called premiers, however; many stones which fluoresce in ultra-violet light show no trace of the bluish color in ordinary light.

prepared borax - Borax pressed into cake form for making jewelers' soldering flux by rubbing cake on slate slab with water.

press - A machine used for production stamping of articles of jewelry. Pressures range from moderate to great. Machines used are foot, screw, electric power, percussion and hydraulic presses.

pressed amber - Poor quality amber and amber chips which have been compressed into a solid, workable block through the application of heat and pressure, in the absence of oxygen. It is difficult to distinguish from the natural amber, but according to Schloss-macher, a drop of ether will leave a dull spot on the pressed amber and have no effect on the natural amber. Pressed amber may be clear or cloudy, and it may be artificially colored. See AMBROID.

pressed copal - Made like pressed amber, from copal fragments and to be distinguished by the same methods as natural copal.

press-fit - A crystal, jewel or object securely positioned through pressure.

pressure blower - Small motor-driven rotary air compressor, for providing blast for soldering, hardening steel, etc., in watch and jewelry trades, in connection with gas supply.

prick punch - A pointed steel punch for marking locations for drilling holes, and other lay-out work.

Friday plume agate - The Friday Ranch in Central Oregon is well known as the source of some of the best of the plume agates, and much of it is traded under the simple name Friday Plume, which is recognized by every amateur lapidary of agates. See PLUME AGATE.

primary cell - A primary source of electrical energy through chemical action. These are not efficiently rechargeable.

primary deposit - A place where minerals or gems are found in the place where they formed, in contrast to alluvial or placer which are derived from the primary deposits and which are termed secondary. A diamond pipe is a primary deposit, the diamond gravels are secondary.

primitive diameter - See GEARING; PITCH DIAMETER.

princess length - Necklace, 18" to 19" in length. See OPERA; CHOKER; MATINEE LENGTH.

princess ring - Dome-shaped ring built up of concentric circles of small stones, such as diamonds, rubies and sapphires.

printed circuit - Electrical circuitry whose electrical continuity and connections are "printed," photo-etched on a non-conductive surface.

prism - In crystallography, a prism is an open form of two or more faces, in parallel pairs, which are parallel to the vertical axis. They always occur in combination with some truncating forms such as pinacoids, domes or pyramids.

prisma - Highly refracting glass.

prismatic quartz - Misnomer for iolite.

profile cutter - A milling cutter which removes material to effect a certain outline such as wheel teeth or molding, etc.

promise ring - A ring popularized by senior high school students in the late Nineteen Sixties, to which manufacturers gave such names as Pre-Posal, First Love and Sweetheart; also known as pre-engagement ring. Often styled as miniature engagement ring with 2-point diamond in Tiffany setting; with the word "love" and small diamond, or heart-shaped setting and small diamond.

prong - One of several wires or claws used to fasten and hold a stone in place. See PRONG SETTING.

prong setting - A setting consisting of a series of prongs or claws to hold a stone. Such settings usually consist of four or six prongs. See CLAMP.

propane - A gaseous hydrocarbon, C2H3, used with air for soldering and other heating actions. Available in small, pressurized tanks for convenient use.

proportion - Diamond grading. One of the two principal factors in cutting grade, the other being "finish" or "symmetry details." Proportion is graded in terms of departure from a standard such as the "Ideal" designed by Marcel Tolkowsky or the "Scan. D.N. Standard Cut." Factors are table diameter, crown height, girdle thickness and pavilion depth, as percentages of girdle diameter. See IDEAL CUT; AMERICAN CUT; TOLKOWSKY, MARCEL; EUROPEAN CUT; EPPLER, W. FR.; SCAN D.N. STANDARD CUT

ProportionScope - Device for the projection of the silhouette of a diamond upon a ground-glass screen, on which facet angles, crown height, girdle thickness and pavilion depth may be compared against ideal proportions; introduced in 1967 by the Gemological Institute of America.

pseudochrysolite - MOLDAVITE.

pseudodiamond - QUARTZ.

pseudoemerald - Theophrastus' name for malachite.

pseudojade - Any of many minerals which have an appearance somewhat similar to jade, serpentine, californite, etc.

pseudomorph - (soo'doe-morf) A natural substitution of one mineral for another with a retention of the original form of the primary mineral during the process. Malachite is frequently pseudomorphous after azurite; in other words, the crystal shape of the azurite is preserved after the mineral is all destroyed. In a sense, petrified wood has silica pseudomorphous after the wood material.

pseudo-succinite - Amber with refractive index of 1.085 from Equilleres, Basses-Alpes, France, which differs from Baltic amber in its reaction to solvents.

Pteria pinquin - Pearl-bearing mollusk of Okinawa and Hong Kong.

pudding stone jade - A variety of nephrite jade which shows light-colored nodules cemented together by darker colored material.

pudding stone jasper - A conglomerate of quartz pebbles cemented together by chalcedony, said to be found in cuttable quality in Michigan. Lightly cemented "pudding-stones" are common in many regions.

puddling - Process for making malleable iron, preparatory to converseon to crucible steel by cementation. See CEMENTATION; CRUCIBLE STEEL; IRON.

puka shell jewelry - Necklaces and other jewelry strung with fragments of seashells, originally found in Hawaii, each being a part of a larger shell and containing a hole; derived from puka, a Hawaiian word meaning "hole;" introduced into the U.S. in 1975.

pulled stone - A synthetic crystal rod made by the Czochralski method, slowly raising a crystallizing rod from a molten bath of suitable composition.

pull winding - Winding by drawing on a string wound around a pulley attached to the mainspring ratchet.

pulse-piece - A metal block, inside a case of a repeater watch, to receive blows of striking hammers, to tell time by touch instead of by ear.

pulsometer - A chronograph watch with dial designed to show the number of pulse-beats per minute, based on an actual count of a less number of beats; a time-saving convenience used by physicians.

pumice - A frothy, light-weight glassy volcanic rock, formed during violent eruptions when gas-filled lava is thrown into the air, where it quickly solidifies before the gases can escape.

pumice powder - An abrasive, made by crushing volcanic rock, used in the jewelry and silver trades for producing non-polished finishes on metals, for a semi-dull finish on varnished wood, etc.

pump drill - A drill-stock used by jewelers for driving various forms of drill points and burrs, mostly in stone-setting work; an interesting survival of a very ancient tool. The drill-chuck, on the end of a steel rod which also carries a fly-wheel, is rotated by two leather thongs which are wound and unwound on the rod by a transverse bar operated up and down by hand.

pump-winding - Early type of keyless watch winding mechanism; the stem is pushed and pulled in and out, operating a ratchet that turns the mainspring arbor. This principle is partly re-adopted in some modern self-winding watches.

punch - A tool, usually of steel for stamping, cutting or perforating.

puncheon - A figured die or punch used by goldsmiths or silversmiths and cutlers.

purity grade - The clarity grade of a diamond. Says CIBJO, the International Confederation of Jewelry, Silverware, Diamonds, Pearls and Stones: "The purity of a diamond must be examined by an experienced professional under 10-power magnification in normal light by means of an achromatic, aplanic lens." See CLARITY GRADE.

purple gold - An alloy of aluminum and gold. Like blue gold it is not a workable alloy.

purple sapphire - A violet corundum, also called oriental amethyst and Bengal amethyst.

pusher - 1. The rod with knob on end for operating the center of a face plate, balance chuck, etc. 2. In stone setting, a handled steel tool used for forcing the bezel around a stone. 3. A similar tool of brass or copper, slightly indented on the end, to push diamonds firmly into prepared holes before fastening by beads, prongs or hammering.

push-piece - A plunger with a head projecting from the center of a watch case, operated by a finger, for setting watches to time, operating chronographs or repeaters, etc. See CHRONOGRAPH; REPEATER.

push-pin-setting - A pin near the case pendant that had to be depressed, simultaneously turning stem to effect the hand-setting. Used in late 19th Century Swiss watches.

putty powder - Oxide of tin, prepared for polishing metals, glass, ivory, and the last stage of some gem stones.

putz pomade - Polishing paste for brass or other metal work too large for buffing on lathe; used by hand rubbing, on cloth or felt pad. Among various formulas the simplest is equal parts of jewelers' powdered rouge and vaseline, mixed thoroughly by stirring by hand or other mechanical means.

puzzle ring - Ring composed of several connected rings that fit together to form one complete design.

pycnometer - (pik-nom'meter). A carefully made water bottle with a drilled glass stopper, which permits it to be invariably filled with the same quantity of water, used for the determination of the specific gravity of unset gems. The stone is weighed in the water and the amount of displaced water is thus determined, this gives the volume of the gem; the loss of weight in water divided into the original weight, gives the density.

pyramid - In crystallography, two pyramids (one inverted) make a closed form, except in the monoclinic and triclinic systems, which truncates all the axes. Bipyramid is a preferable term, but is rarely used, generally pyramid stands for the pair of forms. In the triclinic and monoclinic systems two sets of bipyramids, or a combination with some other forms, are necessary to make a closed form.

pyrite - (pie'rite) Iron sulphide, FeS2, a hard metallic light yellow mineral, commonly found in association with ores. Hardness, 6-6l/2, sp. gr. 4.9-5.2.

pyrometer - An instrument for measuring high temperatures.

pyrope - (pie-rope or pie-rope ee) One of the garnet family, a most consistently red-hued magnesium aluminum silicate, characteristic of volcanic rocks. See BOHEMIAN GARNET; CAPE RUBY, etc.


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