For this method of testing gold that you suspect of being 10 karat value gold
or less, you will test it much the same way you test gold non-destructively with
the scratch test. The only difference is that you would cut the metal of the
unknown gold piece and open it so you can scratch the metal inside the piece
against the testing stone instead of the surface metal. Remember, you should
only use this test if you are unsure of the results you got from the basic
streak test initially or suspect the metal is 10 karat gold or less because the
streak faded but not completely with the application of acid.
This being said, it is important that you try to limit destructive testing as
much as possible to items that either have little aesthetic value, or it can be
easily repaired. And you should always be sure to ask for your customer’s
permission before performing a destructive test on one of their items.
Take your jewelry cutters to cut through the metal so you have an opening in
the piece of gold. This may take several tries to create an opening if the metal
is particularly thick or heavy.
Once you have a cut all the way through the metal, take your jewelry pliers
and pull the metal apart to open the gap. Continue prying the metal apart until
the gap is wide enough or positioned so that you can rub the inside portion of
the metal against the testing plate to create a streak like you did before with
the outside surface of the metal.
Rub the inside section of the metal piece directly against the surface of the
testing stone so that it leaves a mark on the testing stone. Press firmly on the
testing stone to leave a thick and visible deposit that you can test accurately.
The mark should be about 1 to 1 1/2 inches long.
Drop a drop or
two of the 14 karat acid onto the scratch mark you made with the inside metal of
the suspected 10 karat metal piece. Observe the reaction. You are watching to
see if some sort of green bubbles appear where you applied the acid to the metal
marking. Sometimes you may need a jeweler’s loupe to observe the acid reaction
and see if there are actually green bubbles, you can also blot the acid with a
white tissue or napkin to better observe the color of the reaction bubbles which
will give you better viewing contrast than a gold background.
- If the mark
immediately begins to bubble profusely with very green bubbles the item is
either gold filled or gold plated with copper, nickel or a brass alloy
composing most of the metal content of the piece. This is also a common
reaction for gold that is 7 karat gold or less.
- If after 10
seconds, there are only a few green bubbles on the scratch mark on the
testing stone, the item is most likely 9 karat gold. Be aware that 10 karat
white gold will bubble green very slightly when the 14 karat acid is applied
due to the high nickel alloy, so if the metal is white you will have to be
cautious in your identification of the metal.
- If after 10
seconds, there are a number of green bubbles on the mark, the item is going
to be about 8 karat gold.
- If the
scratch mark turns brown immediately and after 10 to 15 seconds of
observation there are no green bubbles the item is a true 10 karat gold.