Cupel 1.5″ Bone ash, each – absorbs 30 grams of lead! The Science of Cupelling – Cupelling is a part of assaying, however it can also be used at any time to prove or disprove precious metals. In other words, cupelling can be used as a mini-assay. If you have anything in which you believe might be gold, silver or platinum, it is simple to) grind a small amount of your substance, mix it with some powdered lead or wrap some lead wool around it, put it in a cupel and place it in the furnace. In about 40 minutes you will have a bead of precious metals or no bead as the case may be. This has been an absolute test of gold, silver, and platinum for over 2000 years.