Dictionary.net

A composition of quicksilver, tin, and sulphur, forming a yellow powder, sometimes used by mediaeval artists, for the sake of economy, instead of gold.

por-p[=o]-r[=e]'n[=o], n. an old alloy of quicksilver, tin, and sulphur, used in place of gold. [It.]

[It.] A mixture of quicksilver, tin, and sulphur, formerly used instead of gold in painting.