In this test, you will use a testing stone to test the surface gold content of an item. This test will give you a loose idea of whether or not the item you are testing is actually gold, but it will not tell you the exact karat content of the metal. Be sure to wash the stone thoroughly with water after each use.
Begin by rubbing or scratching the item you want to test directly onto the surface of the testing stone. You will need to press firmly to leave a thick and visible deposit that you can accurately test. The mark should be about 1 to 1 1/2 inches long.
Next, you will need to make a similar a scratch line with a gold testing needle, you can use any karat gold testing needle, but it is usually best to start with a 14 karat needle since it is one of the most common karat values. Make sure that the mark is very close to the original scratch line so you can test them simultaneously like you need to.
Place a drop or two of the matching acid to the gold testing needle you used on top of the two scratch marks. As soon as the acid hits the testing stone and the marks, watch and compare the speed at which the scratches dissolve.
If the test scratch from the item you are testing dissolves more quickly than the needle scratch mark, it is a lower karat gold than the needle. If the needle scratch dissolves more quickly, the item has a higher gold content.