basic lead carbonate is decomposed on contact with slaked lime, and the hydrated lead oxides that are produced darken on exposure to light. Although Theophrastus apparently places it among the paint pigments, white lead appears to have been little used for painting in ancient times. Pliny remarks, however, that cerussa was suitable for wax painting but not for mural work. In his researches on the colors used in painting by the ancients, Sir Humphry Davy435 noted the absence of white lead on painted walls, and its general absence has been noted in later and more extensive investigations. At the present time it is regarded as one of the most important white pigments, and it has had widespread use in spite of attempts by various governments from time to time to restrict or even prohibit its use on account of its toxic nature. Though the ancients did not use it very much as a paint pigment in a direct way, they did use white lead, and probably lead acetate also, for the production of red lead, which was a substitute for the more expensive natural pigments, cinnabar and realgar.
57. Red copper. The word χαλκό? is a general term used to denote both pure copper and its alloys, though it usually refers to bronze. Here the qualifying adjective "red" indicates that unalloyed copper was employed in the process.
57. grape-residues.
Evidently the genitive τρνγός cannot refer to "wine-lees," which is the usual meaning of τρνξ, but in this context means the residues of the grapes that remain after the must has been pressed out of them, or more strictly, perhaps, such residues in a state of acetous fermentation.
Other ancient writers describe processes for the manufacture of verdigris. Pliny4se gives several mediods. In one of these—probably the same as the one given here by Theophrastus—copper was buried in grape skins and the verdigris was scraped off after ten days. In another method perforated pieces of a copper alloy were suspended in closed casks over vinegar. In a third method vinegar was sprinkled over filings of the metal, and the mixture was stirred
435 Philosophical Transactions of the Royal Society of London, CV (1815), 97-124. «eXXXIV, iio-ii.
