On "Acid Test"

Where does the term "acid test" come from?

In order to figure out what they are buying, a jeweler or broker will drop a bit of acid on the exposed metal of a piece of jewelry, often after making a chink in the surface with a file or sharp tool. Thus, the term "acid test".

Unlike base metals, precious metals, including gold, do not corrode easily. Thus, base metals will fizz or bubble when immersed in acid, while precious metals would remain unaffected.