one of the seven colours into which the rays of light divide themselves when refracted through a glass prism. For an account of the particular structure of bodies by which they appear of a blue colour, see the article Chromatics.—The principal blues used in painting are Prussian blue, bice, Saunders blue, azure, or smalt, verditer, &c.; for the preparation of which, see Colour-Making.—In dyeing, the principal ingredients for giving a blue colour, are indigo and woad. See Dyeing.

Blue Colour of the Sky. See Sky.

Blue Bird. See Motacilla, Ornithology Index.

Blue Fish. See Coryphaena, Ichthyology Index.

Blue Japan. Take gum-water, what quantity you please, and white-lead a sufficient quantity; grind them well upon a porphyry; then take ifinglas's size what quantity you please, of the finest and best smalt, a sufficient quantity; mix them well; to which add, of your white-lead, before ground, so much as may give it a sufficient body. Mix all these together to the consistence of a point.

Blue John, among miners, a kind of mineral which has lately been fabricated into vases and other ornamental figures. It is of the same quality with the cubic spar, with respect to its fusibility in the fire. It loses its colour, and becomes white in a moderate heat: the weight of a cubic foot of the bluest kind is 3180 ounces, and that of the least blue is 3140 ounces. This substance began first to be applied to use about 18 years ago at one of the oldest mines in Derbyshire, called Odin mine, probably from its being dedicated to Odin the great god of the northern nations, at the foot of a high mountain called Mam-Tor in Cafferton. Here the greatest quantities are still found; the largest pieces are sold for gl. a ton, the middle-sized for Gl. and the least for 50s.

Prussian Blue. See Chemistry Index.