The test sample, wrapped in the lead foil, is placed in the cupel for twenty minutes. The lead draws the base metals in the alloy into the cupel and a silver and gold alloy remains in the cupel. This sample is then rolled very thin, annealed, weighed and placed into nitric acid. The acid dissolves the silver and leaves only a gold sample behind. The gold is washed, dried and weighed to give a very accurate percentage of gold in the test alloy.