Chrome yellow

Chrome yellow is lead(II) chromate (PbCrO4). It occurs naturally as the mineral crocoite but the mineral ore was never used as a pigment for paint. 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. Because 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, it was replaced by another pigment, cadmium yellow (mixed with enough cadmium orange to produce a color equivalent to chrome yellow). Darkening may also occur from reduction by sulfur dioxide. Good quality pigments have been coated to inhibit contact with gases that can change their color. The first recorded use of chrome yellow as a color name in English was in 1818. The Piper J-3 Cub aircraft had chrome yellow as its standard overall color, usually called 'Cub Yellow' or 'Lock Haven Yellow' in aviation circles, from the Piper factory that existed in Lock Haven, Pennsylvania, where it was made in the 1930s and during World War II.