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The amount of gold in jewelry is shown in karats. Pure gold is 24K, or 24 of 24 parts gold. Jewelry that's composed of ten parts gold and 14 parts other metals would be marked as "10K" or, decimally, ".416." There is one specific test that determines if a piece of jewelry is made of gold and that test is called the "acid test."

If you wish to find out if a piece of jewelry is made of gold, touch it with a glass stopper which has been wetted with nitric acid. If it is pure gold it will remain untouched and unchanged; if not, the solution will become blue from the formation of nitrate or copper. (False "gold" always contains copper.)

To find the number of karats in a gold object is not as easy as testing for gold content. First, you will need to weigh the gold object. Then use a big object to break the gold into pieces and mix the pieces with silver that measures seven times the weight of the gold mixture. Beat this mixture into thin leaves and then add nitric acid. The silver and copper will dissolve. Now fuse the remaining gold and weigh it.

To fuse the gold back to its original wholeness, you must use a mini-torch at a fair distance and keep the torch moving when applying the flame to the gold at a moderate temperature. Make sure you allow it to cool and then you can compare the first and last weights: the difference will be equal to the number of karats of pure gold. Repeat several times to check.

This exercise or experiment will work with all types of gold, including necklaces, rings, earrings, bracelets, etc. but the larger the piece of jewelry, the better it is to work with.