The basic gold testing procedure is to make a small scratch test of the sample metal you are testing on the test stone. Drop a few drops of the test acid on the sample and observe it. If the quality of the gold is equal to or greater than the karat quality rated on the test acid the acid will not effect the sample. If the tested metal is not gold or is of a lower purity than the quality rated on the test acid the acid will destroy the sample. An optional method is to make two scratches on the stone, one with the sample metal being tested and another with a test needle of known purity gold. When you apply the acid you observe both scratches to see how they compare.
Includes the 10k, 14k, and 18k testing acids along with the 2" x 1 1/2" test stone.