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Brown Pigments
Umbers.-These are made from natural earths which occur in many parts of the world, the finest quality coming from the island of Cyprus.Originally this was imported into this country via Constantinople and was consequently known as "Turkey Umber "a name by which it is still known in the trade. Deposits of the earth are found also in Italy and France and also in this country, in Derbyshire.
Raw umber varies from yellowish brown to dark brown in colour, according to its source.
It can be heat-treated, to produce Burnt Umber, which has a warmer, darker colour.
Both raw and burnt umber can be ground in water, oil, or turpentine and safely mixed with other colours and bases, being valuable owing to their durability and fastness to light and alkalis. The raw variety is unaffected by acids, in which, however, burnt umber is partially soluble.
Both are somewhat transparent and are consequently useful for glazing and in graining work.
Umbers, owing to their manganese oxide content, exert a strong drying influence on linseed oil.
Vandyke Brown.-This pigment, named after the great seventeenthcentury artist who used it extensively, is made from a natural earth, found in various places, but especially in Germany; it is sometimes known as Cologne Earth or Cassel Earth, from its places of origin.
Vandyke brown is prepared in a similar fashion to other earth pigments, though it is also made artificially by the slow burning of cork refuse, beechwood bark, and other decomposed vegetable matter.
It is also produced by mixing lampblack or other good black with iron oxide and toning with yellow ochre, but the result lacks the richness of tone found in the genuine pigment, although it has the advantage of being durable and fast to light, whereas true Vandyke brown is unreliable in these respects.
It can be ground in oil, turpentine, or water, but has poor drying properties.
Sepia.-Sepia is a valuable rich dark reddish-brown pigment, obtained from glands in the common cuttlefish or squib (Sepia officinalis), containing the secretion.
The contents of these glands when dry are treated with dilute alkali, which causes precipitation of the colouring matter.
This is further refined by reprecipitation by means of an acid.
It can be ground in water or oil.
Sepia has high staining qualities, and is fairly stable to light.
It is rather expensive, and only used for high-class decorative painting and photographic images.
It is one of the favourite colours for decoration in monochrome.