Chrome Yellow is a natural yellow pigment made of lead(II) chromate (PbCrO4). It was first extracted from the mineral crocoite by the French chemist Louis Vauquelin in 1809. Because the pigment tends to oxidise and darken on exposure to air over time, and it contains lead, a toxic, heavy metal, it has been largely replaced by another pigment, Cadmium Yellow (mixed with enough Cadmium Orange to produce a colour equivalent to chrome yellow).