1) Blue 2) Bluing 3) Dyestuff 1) Bluing 
The heat treatment of iron or steel which forms a thin surface layer of blue oxide. This retards rusting, and was also used to decorate armour.
The heat treatment of iron or steel which forms a thin surface layer of blue oxide. This retards rusting, and was also used to decorate armour.
In decorating, the term blueing applies to the adding of a small amount of blue to certain white pigments or paints in order to neutralise their yellowish tint and make them appear whiter.