in the religious paintings of the Renaissance. Angels and the Virgin Mary were often portrayed wearing violet robes. The 15th-century Florentine painter Cennino Cennini advised artists: "If you want to make a lovely violet colour, take fine lacca, ultramarine blue (the same amount of the one as of the other)..." For fresco painters, he advised a less-expensive version, made of a mixture of blue indigo and red hematite. 18th and 19th centuries In the 18th century, purple was a color worn by royalty, aristocrats and other wealthy people. Good-quality purple fabric was too expensive for ordinary people. The first cobalt violet, the intensely red-violet cobalt arsenate, was highly toxic. Although it persisted in some paint lines into the 20th century, it was displaced by less toxic cobalt compounds such as cobalt phosphate. Cobalt violet appeared in the second half of the 19th century, broadening the palette of artists with its range of purple colors. Cobalt violet was used by Paul Signac (1863–1935), Claude Monet (1840–1926) and Georges Seurat (1859–1891). Today, cobalt ammonium phosphate, cobalt lithium phosphate and cobalt phosphate are available for use by artists. Cobalt ammonium phosphate is the most reddish of the three. Cobalt phosphate is available in two varieties — a deep less saturated blueish type and a lighter and brighter somewhat more reddish type. Cobalt lithium phosphate is a saturated lighter-valued bluish violet. A color similar to cobalt ammonium phosphate, cobalt magnesium borate, was introduced in the later 20th century but was not deemed sufficiently lightfast for artistic use. Cobalt violet is the only truly lightfast purple pigment with relatively strong color saturation. All other light-stable purple pigments are dull by comparison. The high price of the pigment and the toxicity of cobalt have limited its use. In the 1860s, the popularity of using violet colors suddenly rose among painters and other artists. For example, Vincent van Gogh (1853–1890) was an avid student of color theory. He used violet in many of his paintings of the 1880s, including his paintings of irises and the swirling and mysterious skies of his starry night paintings, and often combined it with its complementary color, yellow. In his painting of his bedroom in Arles (1888), he used several sets of complementary colors; violet and yellow, red and green and orange and blue. In a letter about the painting to his brother Theo, he wrote, "The color here...should be suggestive of