The Natural History of Pliny, Volume 6 (of 6)

There are two kinds of silver. On placing a piece of it upon an iron fire-shovel at a white heat, if the metal remains perfectly white, it is of the best quality: if again it turns of a reddish colour, it is inferior; but if it becomes black, it is worthless. Fraud, however, has devised means of stultifying this test even; for by keeping the shovel immersed in men’s urine, the piece of silver absorbs it as it burns, and so displays a fictitious whiteness. There is also a kind of test with reference to polished silver: when the human breath comes in contact with it, it should immediately be covered with steam,1040 the cloudiness disappearing at once.