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COMMENTARY
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red ochre pigments appear to indicate that this was their practice. Most of the light-red or pink pigments examined by Midgley400 contained considerable proportions of calcium carbonate, probably present as an intentional addition, and one such pigment contained both calcium carbonate and calcium sulfate, which is almost certainly a sign of deliberate admixture. Apparently the artists lightened the color of dark-red ochres by mixing them with chalk or other white pigments. Theophrastus also seems to imply that the inferior light-red ochres containing too little ferric oxide were sometimes mixed with ochres containing a higher proportion of ferric oxide in order to produce pigments of the desired depth of color. Attempts to confirm this by chemical analysis have not been successful, as such mixed ochres apparently cannot be distinguished in this way from natural ochres.
53. It is also made by burning yellow ochre, but this is an inferior \ind.
It is not necessarily true that red ochre artificially produced by roasting yellow ochre is inferior to natural red ochre, but since most yellow ochres contain a considerable proportion of sand and clay, the final product usually has a lower proportion of ferric oxide and, for this reason, a lower tinting strength when mixed with white pigments. Dioscorides401 says that the manufactured red ochre is inferior to the kind from Sinope, which, as indicated in the notes on section 52, was probably a natural red ochre containing an unusually high proportion of ferric oxide. Vitruvius402 states, however, that burnt ochre was very useful for stucco work.
53. Kydias. Probably this is the artist Kydias mentioned by Pliny,408 who refers to his most important painting and says that he flourished at the same time as Euphranor, who distinguished himself far beyond all other artists in the hundred and fourth Olympiad.404 Therefore Kydias' discovery was probably made about half a century before Theophrastus described it. It is uncertain, and perhaps doubtful, whether Kydias was the first to discover how
400 "Chemical Analysis of Ancient Athenian Pigments," pp. 18-21. *01V, 112 (Wellmann ed., V, 96). *02 VII, 9, 2.
*03XXXV, 128, 130. ««364.36ο B.C.
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