White lead

White lead compounds known as lead soap were used as additive for lubricants for bearings and in machine shops. Lead soap was also used as an oil drying agent for paints made with drying oil or air drying paints made with alkyd resins. Lead is often used with cobalt driers. Lead free substitutes have been developed to replace this use of lead in paint. A second basic lead carbonate is known with the formula . ==History==

What is commonly known today as the "Dutch method" for the preparation of white lead was described as early as Theophrastus of Eresos (ca. 300 BC), in his brief work on rocks or minerals, On Stones or History of Stones. His directions for the process were repeated throughout history by many authors of chemical and alchemical literature. The uses of cerussa were described as an external medication and pigment. According to Suda, Thespis before he introduced the mask in the ancient theater, he performed having rubbed his face with white lead . The Roman Emperor Elagabalus was said to have used white lead and Alkanet as eye makeup. Clifford Dyer Holley quotes from Theophrastus' History of Stones as follows, in his book The Lead and Zinc Pigments. Later descriptions of the Dutch process involved casting metallic lead as thin buckles and corroded with acetic acid in the presence of carbon dioxide. This was done by placing them over pots with a little vinegar (which contains acetic acid). These were stacked up and covered with a mixture of decaying dung and spent tanner's bark, which supplied the CO2, and left for six to fourteen weeks, by which time the blue-grey lead had corroded to white lead. The pots were then taken to a separating table where scraping and pounding removed the white lead from the buckles. The powder was then dried and packed for shipment or shipped as a paste. One benefit of the process was that it was not necessary to dry the paste of white lead, removing its water. All that needed was to mill the paste with linseed oil, and the white lead would take up the oil and reject the residual water, to give white lead in oil. ==Paints==

White lead has been mostly supplanted in artistic use by titanium white, which has much higher tinting strength than white lead. Critics argue that substitutes like zinc oxide and titanium dioxide are more reactive, become brittle, and can flake off. White lead is less used by today's painters, not because of its toxicity directly; but simply because its toxicity in other contexts has led to trade restrictions that make white lead difficult for artists to obtain in sufficient quantities. Winsor & Newton, the English paint company, was restricted in 2014 from selling its flake white in tubes and now must sell exclusively in tins. In the eighteenth century, white lead paints were routinely used to repaint the hulls and floors of Royal Navy vessels, to waterproof the timbers and limit infestation by shipworm. Other synonyms (as an art pigment) Among the synonyms for white lead are Berlin white, Cremnitz white, Dutch white lead, flake white, Flemish white, Krems white, London white, Pigment White 1, Roman white, silver white, slate white and Vienna white. == See also ==