Assay Reagent

an agent used on a touchstone to determine the fineness of jewelry, domestic goods, and alloys made of noble metals.

Gold chloride solutions and acidic reagents are used in assaying gold articles, whereas silver nitrate solutions are used in assaying silver articles. Platinum is assayed by means of acidic reagents or solutions of potassium iodide, hydrochloric acid, or nitric acid. A potassium iodide reagent is used in determining the fineness of palladium.