PIGMENTS 135
saffron, indigo; synthetic or coal-tar colors are those like magenta, alizarin, and
toluidine red. Although a few organic pigments are stable and are considered
permanent, in general they are fugitive.
Orpiment (King's yellow) was once widely used, particularly in the East, but
has now fallen into complete disuse because of its limited supply and because of
its poisonous character. It is the yellow sulphide of arsenic, AssS3, occurring
naturally in many places but not in large quantities. The principal sources in
ancient times appear to have been in Hungary, Macedonia, Asia Minor, and
perhaps in various parts of Central Asia. There was a large deposit near Jula-
merk in Kurdistan (see Dana, p. 358). It is said that some hundreds of tons of
orpiment are exported annually from Shih-haung-Ch'ang in Yunnan province in
China (see Thorp). The natural product must have been prepared by methods
" common for other natural pigments. It can also be made artificially by precipita-
tion or sublimation. Orpiment is brilliant, when pure, with a rich, lemon-yellow
tone, and fair covering power. Laurie says (eThe Identification of Pigments . . . /
p. 165): 'The brilliant color and tint on a MS. are usually unmistakable/ In old
paintings and illuminations, it was rather coarsely ground to preserve its rich
yellow color. Microscopically, the larger particles glisten by reflected light and
have a waxy-looking surface. It often contains orange-red particles of realgar,
to which it is closely related (see Realgar). Orpiment is crystalline (monoclinic)
and is highly refracting. It sometimes appears to have a fibrous structure. This
natural sulphide is stable to light and air. It is not affected by dilute acids and
alkalis but only by strong acids. When ignited, it burns to arsenic trioxide. Since
it is a sulphide, it is incompatible with copper and with some lead pigments.
Orpiment was known in classical times. It is mentioned by Pliny (see Bailey,
I, 101) as occurring in Syria, and as a pigment which can not be used in fresh
plaster (op. cit.> II, 91). It appears to get its name from a corruption of the Latin,
auripigmentum (gold color or paint). By Vitruvius it is mentioned (VII, Chap.
VII) among the natural colors. Spurrell records it as having occurred in Egyptian
paintings at Tell el Armarna of the XVIII Dynasty. Lucas (p. 292) says that
the mineral does not occur in Egypt and must have been imported, perhaps from
Persia. It has been identified many times in old illuminations. Laurie (The Pig-
ments and Mediums of the Old Masters^ p. 72) reports a peculiar kind on VIII
century Irish manuscripts. He says, also, that it was used on Byzantine and on
early Persian pages (see 'The Materials in Persian Miniatures/ pp. 146-147).
It has been found, along with realgar, on mud wall paintings from Kara Khoto
in Central Asia (XI-XIII centuries). Although it was mentioned by Cennino
Cennini (see Thompson, The Craftsman's Handbook, p. 28), it does not much
appear in easel or monumental painting of the West. De Wild did not find it on
any of the Dutch and Flemish paintings he examined, perhaps because it was
not necessary when a good grade of massicot was available.
Oyster Shell White (see Chalk).