The Roman sandaracha seems to have had various significations. Pliny speaks of the different shades of sandaracha; there was also a compound color of equal parts of sandaracha and rubrica calcined, called sandyx, which Sir H. Davy supposed to approach our crimson in tint; in painting it was frequently glazed with purple, to give it additional lustre.
Yellow.—Yellow-ochre, hydrated peroxide of iron, the sil of the Romans, formed the base of many other yellows, mixed with various colors and carbonate of lime. Ochre was procured from different parts—the Attic was considered the best; sometimes the paler sort of sandaracha was used for yellow.
Green.—Chrysocolla, which appears to have been green carbonate of copper, or malachite (green verditer), was the green most approved of by the ancients; there was also an artificial kind which was made from clay impregnated with sulphate of copper (blue vitriol) rendered green by a yellow dye. The commonest and cheapest colors were the Appianum, which was a clay, and the creta viridis, the common green earth of Verona.
Blue.—The ancient blues were very numerous; the principal of these was cœruleum, azure, a species of verditer, or blue carbonate of copper, of which there were many varieties. The Alexandrian was the most valued, as approaching the nearest to ultramarine. It was also manufactured at Pozzuoli. This imitation was called cœlon. Armenium was a metallic color, and was prepared by being ground to an impalpable powder. It was of a light blue color. It has been conjectured that ultramarine (lapis lazuli) was known to the ancients under the name of Armenium, from Armenia, whence it was procured. It is evident, however, from Pliny's description, that the "sapphirus" of the ancients was the lapis lazuli of the present day. It came from Media.
Indigo, indicum, was well known to the ancients.
Purple.—The ancients had several kinds of purple, purpurissimum, ostrum, hysginum, and various compound colors. Purpurissimum was made from creta argentaria, a fine chalk or clay, steeped in a purple dye, obtained from the murex. In color it ranged between minium and blue, and included every degree in the scale of purple shades. The best sort came from Pozzuoli. Purpurissimum indicum was brought from India. It was of a deep blue, and probably was the same as indigo. Ostrum was a liquid color, to which the proper consistence was given by adding honey. It was produced from the secretion of a fish called ostrum, and differed in tint according to the country from whence it came; being deeper and more violet when brought from the northern, redder when from the southern coasts of the Mediterranean. The Roman ostrum was a compound of red ochre and blue oxide of copper. Hysginum, according to Vitruvius, is a color between scarlet and purple. The celebrated Tyrian dye was a dark, rich purple, of the color of coagulated blood, but, when held against the light, showed a crimson hue. It was produced by a combination of the secretions of the murex and buccinum. In preparing the dye the buccinum was used last, the dye of the murex being necessary to render the colors fast, while the buccinum enlivened by its tint of red the dark hue of the murex. Sir H. Davy, on examining a rose-colored substance, found in the baths of Titus, which in its interior had a lustre approaching to that of carmine, considered it a specimen of the best Tyrian purple. The purpura, as mentioned in Pliny, was an amethyst or violet color.
Brown.—Ochra usta, burnt ochre.—The browns were ochres calcined, oxides of iron and manganese, and compounds of ochres and blacks.
Black.—Atramentum, or black, was of two sorts, natural and artificial. The natural was made from a black earth, or from the secretion of the cuttle-fish, sepia. The artificial was made of the dregs of wine carbonized, calcined ivory, or lamp-black. The atramentum indicum, mentioned by Pliny, was probably the Chinese Indian ink.
White.—The ordinary Greek white was melinum, an earth from the Isle of Melos; for fresco-painting the best was the African parœtonium. There was also a white earth of Eretria and the annularian white. Carbonate of lead, or white lead, cerussa, was apparently not much used by the ancient painters. It has not been found in any of the remains of painting in Roman ruins.
Methods of Painting.—There were two distinct classes of painting practiced by the ancients—in water colors and in wax, both of which were practiced in various ways. Of the former the principal were fresco, al fresco; and the various kinds of distemper (a tempera), with glue, with the white of egg, or with gums (a guazzo); and with wax or resins when these were rendered by any means vehicles that could be worked with water. Of the latter the principal was through fire, termed encaustic.