Prussian Black
:
ON THE NEUTRAL, BLACK.
The same Prussian blue which gives a brown when burnt in the open air,
yields a black when calcined in a close crucible. Very intense, very
soft and velvety, and very agreeable to work, this bluish-black dries
much more promptly than most other blacks, and scarcely requires
grinding. On account of its extreme division, however, it would probably
be found more energetic as a decolourising agent in admixture with
organic pigments than most carbonaceous blacks.
Another Prussian black, containing copper, and made by a wet process, is
obtained when a dilute solution of cupric sulphate and ferrous sulphate,
in proper proportions, is mixed with a quantity of ferrocyanide of
potassium not in excess. A very bulky deep black precipitate is formed,
which is difficult to wash, and is deep black when dry. It is insoluble
in water, and appears to be a compound analogous to Prussian blue. As a
pigment, this black is inferior to the preceding.