A Sample Which Parts With Its Prussiate To Cold Water Is Quite





unfitted for the palette, for which the most perfect specimen is none

too stable.



In spite of the learned researches of Professor Williamson, whose name

is as closely connected with the pigment as are the names of Schunck and

De La Rue with madder and cochineal, Prussian blue is not yet entirely

understood. Complex and uncertain in composition, uncertain too in its

habitudes, our best course perhaps will be not to attempt a complete

survey, but to state briefly those facts which bear on the artist's

craft.



Prussian blue is a colour of vast body and wonderful transparency, with

a soft velvety richness, and of such intense depth as to appear black in

its deepest washes. Notwithstanding it lasts a long time under

favourable circumstances, its tints fade by the action of strong light;

becoming white, according to Chevreul, in the direct rays of the sun,

but regaining its blue colour in the dark; hence that subdued light

which is favourable to all colours is particularly so to this blue. Its

colour has the singular property of fluctuating, or of coming and going,

under certain conditions; and which it owes to the action and reaction

by which it acquires or relinquishes oxygen alternately. It also becomes

greenish sometimes by a development of the oxide of iron; and is

purpled, darkened, or otherwise discoloured by damp or impure air. Time

has a neutralizing tendency upon its colour, which forms tints of much

beauty with white lead, though they are not equal either in purity,

brilliancy, or permanence to those of cobalt and ultramarine. When

carefully heated, Prussian blue gives off water and assumes a pale green

hue; its colour, therefore, depending on the presence of water, must not

be exposed to a high temperature. And as it is likewise injured or

destroyed by alkalis, which decompose it into oxide of iron and a

soluble prussiate, the blue should be avoided in fresco, on account of

the lime; neither should it be employed with pigments of an alkaline

nature, nor with hard water containing bicarbonate of lime in solution,

but with clean rain or distilled water, either of which is preferable

for colours generally.



Prussian blue dries and glazes well in oil, but its great and principal

use is in painting deep blues, in which its body helps to secure 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, to the intensity of which it adds

considerably. Prussian blue borders slightly on green, a quality which

militates against its use in skies and distances. In spite, however, of

its want of, or deficiency in, durability, the old water-colour painters

so employed it, neutralized by the addition of a little crimson lake. It

is serviceable in mixed tints of greens, affording with light red a

sea-green neutral. Dissolved in oxalic acid, the blue is available as an

ink, or for tinting maps.





A Pure Azure Like A Spot Of Light While Their Ground The Prussian All Cases Add The Property Of Being Innoxious As This However facebooktwittergoogle_plusredditpinterestlinkedinmail

Feedback