We use nitric acid to determine whether or not a piece is gold,
usually applying a drop or two after scratching with a sharp scribe.
Not-gold reacts with green fizz. Sometimes a brownish stain is left
by the acid, even on solid gold. It seems to happen mostly when
testing lower karat gold. It is easily polished off.
Is this an accurate test, y’all? It seems to work pretty well, as
far as I know.
Zombie Bench Jeweler who can’t sleep on Christmas Eve