 After the French chemist Louis Vauquelin discovered the new element chromium in 1797 lead chromate was synthesized in the laboratory and used as a pigment beginning in the second decade of the nineteenth century.Chrome yellow had been commonly made by mixing solutions of lead nitrate and potassium chromate and filtering off the lead chromate precipitate.The pigment tends to react with hydrogen sulfide and darken on exposure to air over time, forming lead sulfide, and it contains the toxic heavy metal lead plus the toxic, carcinogenic chromate.