Pure 24 carat gold is a soft, malleable metal. In jewellery manufacturing, it is usually alloyed with other elements such as silver and copper to increase its hardness and to improve its wear resistance. Gold jewellery is stamped with a carat rating to define the amount of pure gold contained within its alloy. Although copper and brass resemble gold when polished, these metals are almost worthless in small amounts. A gold test kit will tell you if a piece of metal is gold or copper.
Score a half-inch line on the flat black test stone provided in the gold test kit by rubbing the edge of the metal up and down against its surface two or three times. This will leave a thin line of metal particles embedded in the stone.
Place a small droplet of acid from the squeeze bottle marked "14 karat" on one end of the line. If the line fizzes, turns green and disappears, the piece of jewellery is made of copper or brass. If the line fades but does not disappear altogether, the piece is made out of gold with a lower rating than 14 carat. If the line discolours slightly, but remains, the piece is made out of 14 carat gold. If the line stays bright without discolouring the jewellery has a higher rating than 14 carat.
Squeeze a droplet of 18 carat test acid onto the middle of the yellow line. If the line fades slightly, the piece being tested is 18 carat. If it remains bright, the jewellery is made out of 22 carat gold. You can prove this by placing a droplet of 22 carat test acid on the remaining part of the line.
Wear latex gloves when doing a gold acid test.