The best quality of Cyprus raw umber has a peculiar greenish cast, which we usually term olive, and its color is due to ferric oxide of iron and quite a large percentage of dioxide of manganese, to which latter is also due its good drying quality when ground in linseed oil. Some specimens have a somewhat dull reddish or yellowish cast. These, however, produce a poor tint with white. The olive toned raw umber, makes a much warmer tint and is especially favored by artists and decorators. Raw Cyprus umber consists essentially of hydrated ferric oxide of iron, manganese dioxide and silica and silicate of alumina, with lime in small percentage and minute portions of phosphoric acid. A very good sample of Cyprus raw umber, after drying out all the hygroscopic moisture, gave the following analysis: - Combined water, 8.84 per cent; ferric oxide, Fe2O3, 51.20 per cent.; manganese dioxide, MnO2, 13.16 per cent.; carbonate of lime, CaCO3, 2.12 per cent.; alumina, A12O3, 3.18 per cent.; silica, SiO2, 21.27 per cent.; phosphoric acid, P2O5, 0.23 per cent. Total, 100 per cent
Against this we will mention the analysis of a sample of bone dry American raw umber, which was considered the best specimen of that class found in a number of years: - Combined water, 10.85 per cent.; ferric oxide, Fe2O3, 20.13 percent.; manganese dioxide, MnO2, 9.26 per cent.; carbonate of lime, CaCO3, 6.12 per cent.; alumina, A12O3, 13.37 per cent.; silica, SiO2, 27.56 per cent.; calcium sulphate (gypsum), CaCO4, 2.71 per cent. Total, 100 per cent.
This specimen of American raw umber when rubbed out in oil had a yellowish brown tone, as against the olive of the Cyprus umber and lacked the semi-transparency of the latter, as well as its richness. Had a dull appearance in comparison, that a practical painter would describe as having "no life" In testing the staining power or strength for staining white, the Cyprus specimen gave a strong, warm, brownish tint with a tinge of green, while the American umber produced with the same white a weak, cold stone gray.