Colour of South Drawing Room: Turner's patent yellow

"Patent yellow, also known as Turner's yellow (PbC12. 5-7PbO) was patented by James Turner of England in February 1781, hence its name. Turner noted Scheele's discovery as applicable for, "a method of producing a yellow colour for painting in oil or water, making white lead, and of separating the mineral alkali from common salt, all to be performed in one single process" (Harley 1970, 91-92). The yellow pigment was made by grinding together, in water, two parts of lead (either red lead or litharge) and one part of sea salt. The mixture was allowed to stand for twenty-four hours. A caustic soda solution was poured off and the remaining white substance was heated (and dried) until it reached the desired shade of yellow.

Turner's patent did not prevent other manufacturers from copying his process. He sued one competitor and won the case on appeal in 1787. The case was published in books on patent law because it was won on a ruling that stated that if a patentee claimed to do several things by one process and one failed; the whole patent was void. In fact, Turner had listed several different names for lead and for the type of salt that could be used. Turner's competitor could not prove definitively that variations in the raw materials would not produce the pigment and Turner retained his patent.

A statute ordered by an Act of Parliament extended the time allowed to Turner as the sole manufacturer because competitors had taken his rightful income. It went on to state that Turner's yellow was superior and less costly than orpiment. It contributed to the National income of England and to the salt tax in that it was made from native raw materials.

Turner's yellow was widely used in England and regarded as durable and bright. It was sold at one shilling per watercolor cake in spite of a known tendency to blacken. Field claimed that it worked well in both oil and watercolor but noted its impermanence in sunlight.

In spite of the introduction of more permanent yellows in the nineteenth century, it was produced on a large scale. C. T. Kingzett, author of The History, Products and Processes of the Alkali Trade, 1877, recorded its production at a soda factory at Walker-upon-Tyne, England, where it was sold as Turner's Patent Yellow. At the Great Exhibition of 1851, an example of its use in oil was provided by the Washington Chemical Company of Washington, Durham, England (Harley 1970, 91-92)."

Still need to find somewhere to stock it. Can buy here (ebay).
Think this is the Green paint in the Loggia though.