Blueing, is the art of communicating a blue colour to different kinds of substances. Laundresses blue their linen with smalt; dyers, their stuffs and wools with woad or indigo.

Blueing 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.

Blueing of iron, is a method of beautifying that metal for mourn-ing buckles, swords, etc. The process is as follows : Take a piece of grind-stone or whet-stone, and rub hard on the work, to take from it the black scurf, : then heat it in the fire, and as it grows hot, the colour changes by degrees, appearing first of a light, then of a darker gold colour, and lastly of a blue. Some-' times they also grind indigo and salad-oil together; and rub the mixture on the work, while it is heating, with a woollen rag, leaving it to cool gradually.