Sepia is furnished by the cuttle-fish (Sepia officinalis). The colour is extracted from a pocket filled with a brown liquor, which the fish emits to obscure the water when pursued. As soon as caught, this pocket is removed, dried in the sun, powdered, ground with a concentrated solution of potash carbonate, and boiled for some time. The solution is filtered, saturated with an acid, and left to settle. The precipitate is washed, first by decantation, and afterwards upon a filter, and then dried. This pigment forms an impalpable powder of a dark brown colour, insoluble in water or alcohol, and very fine and durable.
Sienna is an earthy substance, exported from Tuscany, and owes its colour to a hydrated oxide of iron. It is used raw or burnt. Raw sienna has a dark yellow exterior, and a light yellow interior; its powder is greenish yellow. Burnt sienna is either light or dark red when in lumps, but its powder is dark red.
Umber appears to be a hydrated silicate of iron and manganese, found native in brown lumps, adhesive to the tongue, staining the flesh, and falling to powder in water. The impurities are removed by washing, and the floated article, after settling, forms a light brown powder, which is used raw or burnt. Powdered umber, or that which has been calcined too much, reddens or blackens by the dehydration of the iron, or the superoxidization of the manganese. It is rarely employed alone, but mingles well with other colours and with slaked lime.
Vandyke-brown is derived from iron, and is very durable. It is prepared by the calcination of yellow ochres. The resulting frit is sold in lumps, grains, or impalpable powder. A Vandyke-brown is also manufactured by calcining sulphate of iron several times. The proper colour is arrived at by practice. This latter brown, which is entirely an iron oxide, and of purer colour than the preceding, is more expensive. It is often adulterated with the brown frit, a fraud detected by concentrated hot acids, which easily dissolve the pure oxide of iron, and with difficulty the ochre-brown. By mixing Vandyke-brown with red ochre and manganese binoxide, very durable browns are obtained, which do not require driers when used hot. Other durable browns may be prepared by mixing this pigment with lamp- or ivory-black.