BLUING of Metals

BLUING of Metals is the process of heating them in the

Bluff-Headed
Blumenbach.

fire till they assume a blue colour. The bluing of iron is done thus: A piece of grindstone or whetstone is rubbed hard on the work to take off the black scurf; the iron is then heated in the fire, and as it grows hot the colour changes 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. Among sculptors is used the term 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.