French Prussian-brown
:
ON THE SEMI-NEUTRAL, BROWN.
According to Bouvier, a colour similar to that of bistre, and rivalling
asphaltum in transparency, is produced by partially charring a
moderately dark Prussian blue; neither one too intense, which gives a
heavy and opaque brownish-red, nor one too aluminous and bright, which
yields a feeble and yellowish tint. Yielding to a rapture we cannot
wholly share, he describes its qualities in the warmest terms. In his
opinion,
it has the combined advantages of asphaltum, mummy, and raw
Sienna, without their drawbacks. "I cannot," he says, "commend too
highly the use of this charming bistre-tint: it is as beautiful and good
in water as in oil, perfectly transparent, of a most harmonious tone,
and dries better than any other colour suitable for glazing. Closely
resembling asphaltum in tint as well as in transparency, this brown is
preferable to it in every point of view." As the colour is very quickly
and easily obtained, the artist can judge for himself of its proper
value. M. Bouvier's process is, to place upon a clear fire a large iron
spoon, into which, when red hot, some pieces of the Prussian blue are
put about the size of a small nut: these soon begin to crackle, and
throw off scales in proportion as they grow hot. The spoon is then
removed, and allowed to cool: if suffered to remain too long on the
fire, the right colour will not be produced. When the product is crushed
small, some of it will be found blackish, and the rest of a yellowish
brown: this is quite as it should be. Chemically, the result is a
mixture of oxide of iron and partly undecomposed or carbonised
prussiate.