BLUING, the art or art of communicating a blue colour to bodies.
BLUING of Metals is performed by heating them in the fire till they assume a blue colour. It is 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 for mourning buckles, swords, watch-springs, and the like. It is done thus: Take a piece of grindstone or whetstone, and rub hard on the work to take off the black scurf; then heat it in the fire, and as it grows hot the colour will change by degrees, becoming first of a light, then of a darker gold colour, and lastly blue. Sometimes also indigo and salad-oil are ground together, and the mixture rubbed on the work with a woollen rag while it is heating, after which it is left to cool of itself. Among sculptors we find mention made of bluing a figure of bronze, by which is meant the heating of it, to prepare it for the application of gold leaf; and it is so called because of the bluish cast the metal acquires in the operation.