French Prussian-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


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