Prussian Blue, otherwise called Berlin blue, Parisian blue, Prussiate of Iron, Cyanide of Iron, or. in language more pedantically chemical, Per-ferro-cyanate of Iron, with alumina, etc, is rather a modern pigment, produced by the combination of the prussic or hydro-cyanic acid, iron, and alumina. It is of a deep and powerful blue colour, of vast body and considerable transparency, and forms tints of much beauty with white lead, though they arc by no means equal in purity and brilliancy to those of cobalt and ultramarine, nor have they the perfect durability of the latter.

Notwithstanding Prussian blue lasts a long time under favourable circumstances, its tints fade by the action of strong light, and it is purpled or darkened by damp or impure air. It becomes greenish also sometimes by a developement of the yellow oxide of iron. The colour of this pigment has also the singular property of fluctuating, or of going and coming, under some changes of circumstances; which property it owes to the action and reaction by which it acquires and relinquishes oxygen alternately: and time has a neutralizing tendency upon its colour.

It dries and glazes well in oil, but its great and principal use is in painting deep blues; in which its body secures its permanence, and its transparency gives force to its depth. It is also valuable in compounding deep purples with lake, and is a powerful neutralizer and component of black, and adds considerably to its intensity. It is a pigment much used in the common offices of painting, in preparing blues for the laundress, in dyeing, and in compounding colours of various denominations. Mineralogists speak of a Native Prussian Blue.

2. Antwerp Blue

Antwerp Blue is a lighter-coloured and somewhat brighter Prussian blue, or ferro-prussiate of alumine, having more of the terrene basis, but all the other qualities of that pigment, except its extreme depth. Haerlem Blue is a similar pigment.