An acid test is any qualitative chemical or metallurgical assay which uses acid; most commonly, and historically, the use of a strong acid to distinguish gold from base metals. Figuratively, acid test is any definitive test for some attribute or of the performance of some product. The traditional acid test for gold consists of placing a small drop of a strong acid, such as nitric acid, onto the metal's surface. Most metals fizz or bubble, while precious metals remain unaffected. The acid test is thus decisive, immediate, cheap and simple to perform.