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 insignass 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 paint.
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 Castleton. Here the greatest quantities are still found; the largest pieces are sold for £1 a ton, the middle-sized for 6l. and the least for 5s.
Prussian Blue. See Chemistry Index.
BLUING, the act or art of communicating a blue colour to bodies otherwise destitute thereof. Laundresses blue their linen with smalt; dyers their stuffs and wools with woad or indigo.
BLUING of Metals is performed by heating them in the fire till they assume a blue colour; particularly practised by gilders, who blue their metals before they apply the gold and silver leaf.
BLUING of Iron, a method of beautifying that metal sometimes practised; as for mourning buckles, swords, and the like. The manner is thus: Take a piece of grindstone or whetstone, and rub hard on the work, to take off the black scurf from it: then heat it in the fire; and as it grows hot, the colour changes by degrees, coming first to light, then to a darker gold colour, and lastly to a blue. Sometimes they also grind indigo and salad-oil together; and rub the mixture on the work with a woollen rag, while it is heating, leaving it to cool of itself. Among sculptors we also find mention of bluing a figure of bronze, by which is meant the heating of it, to prepare it for the application of gold-leaf, because of the bluish cast it acquires in the operation.