Blue. The blue pigments in common use by artists are few in number, and consist of native and Artificial Ultramarine, Cobalt, Indigo, and Prussian Blue (q.v.). Genuine ultramarine, prepared from the mineral lapis lazuli, and ordinary cobalt blue, sold for artists' work, are permanent colours. They are used either alone, or mixed with other pigments, chiefly for skies and distances in landscape; and by themselves, or to make up grays and other mixed tints in figure-painting. Owing to the exceptionally high price of real ultramarine, the artificial colour, which is of doubtful permanency, is usually substituted for it. Prussian blue and indigo are highly useful colours, since it is only these that yield dark blues, and only from them, mixed with yellows or browns, that strong greens can be obtained. It is unfortunate accordingly that both are more or less fugitive. All the blues above named are used both in oil and water-colour painting, but indigo less than the others in oil, since it is most apt to fade in that medium.
A number of different names are used in commerce for what is essentially the same pigment, or for pigments closely resembling one another. The following statement gives some explanation of these.
Cobalt blues are mixtures of cobalt with earthy or metallic bases, which have been subjected to the action of heat, and have received the following names: Cobalt blue, cerulean blue, royal blue,
Dumont's blue, Saxon blue, Thénard's blue, Leithner's blue, Hungary blue, Zaffre or enamel blue, Vienna blue, azure blue, and Paris blue. The last name is also applied to a Prussian blue, and azure is also given to a variety of ultramarine blue.—Smalt is a powdered cobalt glass used in illumination and flower-painting.—Artificial ultramarine is also called French ultramarine, French blue, new blue, and permanent blue. Coarse qualities of this colour are largely used by house-painters.—Intense blue is a refined indigo.—Prussian blue (sesquiferrocyanide of iron) is otherwise named Berlin blue, Paris blue, and ferrocyanide of iron. The name Paris blue is also given to a cobalt colour.—Antwerp blue is a variety of Prussian blue made lighter by the addition of an aluminous base, and not so permanent.—Blue ochre (hydrated phosphate of iron) is a subdued permanent blue, but not much employed.—Blue verditer is a hydrated oxide of copper which changes and ultimately blackens by time. It is used in distemper work and paper-staining.
Blue was worn as a distinctive colour by the Scottish covenanters, and is in some places used by Conservatives. The traditional Whig colour was blue also, or blue and buff. Navy blue is a dark blue. Dark blue is the Oxford colour, light blue the Cambridge one.
For Blue Dyes, see DYEING; and for blue colours used in the manufacture of GLASS and POTTERY, see these heads. Blueing is a name for indigo or any material used for giving a bluish colour to linen. See also TEMPERING.