Identifying gemstones is a complex process, even if you know what type of stone you have determining whether it is natural or synthetic, treated or dyed or anything else can seem impossible. But with the right tools this can be done without an expensive lab or a gemologist. A dichroscope separates a transparent gemstones (crystal) colors into 2 wavelengths or colors (dichroic) that are often seen as one by the human eye, this is of course if there is more than one in the stone. By comparing these results with the known properties of gemstones can be used to help identify the gemstone. Below is a more technical explanation of the calcite dichroscope.
Transparent gemstones or crystals produce colors, as it selectively absorbs some wavelengths of light, while allowing others to pass through to the viewer creating the color of the gemstone. Gemstones can produce a single color (single refractive), or multiple colors which often appear as one color to the human eye. A dichroscope is used to detect pleochroism in gemstones, pleochroism is an optical phenomenon in which an object being viewed appears to be different colors when observed at different angles. A calcite dichroscope, separates the colors in the crystal by separating the slow and fast waves of light and displaying them on 2 screens inside the dichroscope. If the colors that are displayed are the same then the crystal is isotropic or single refractive, if they are different, the gemstone is anisotropic and could be uniaxial or biaxial, meaning they have one or two optical axes. This test must be done at 5 points around the stone as pleochroism shows color varies by the angle the object is viewed at. By determining if the gemstone is anisotropic (displays pleochroism) or isotropic, gemologist can start to determine what gemstone they are looking at and if it is natural or synthetic and treated with dyes and other artificial effects. There are two types of dichroscopes available, polarizing which only shows one spectrum of light at a time using polarizing filters making it difficult to identify slight variations in color shades and the more popular type, calcite dichroscopes which uses a rhomb or rhombus shaped piece of calcite which allows isolated wavelengths of light to pass through and be viewed individually in two (dichroic) colors, which can easily be compared and contrasted on the spot, making is much more convenient than a polarizing dichroscope.
How to use a Calcite Dichroscope:
As with any other instrument, proper use will determine if you get accurate results. The stone is held close to the aperture, even slightly touching it, with a strong allochromatic, white light source behind the stone. When one looks through the other end of the dichroscope, two small windows next to each other will be seen with a color in each of the windows. These colors may either be the same or different colors or different shades of colors. Now turn the dichroscope slowly 180° between your fingers while keeping the stone in a fixed position and observe if the colors in the two windows are the same or if they differ.
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