varying in hue, is obtainable, in the form of prussiate, &c., but cannot be recommended, however made.
265. 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 prussiate.
266. Gambogiate of Iron.
Dr. Scoffern read a paper at the Meeting of the British Association of Science, in 1851, describing this combination as a rich brown, like asphaltum, but richer, as well as more durable in oil. It has not been, however, employed as a pigment, or at least is not at present.
267. Hypocastanum,
or Chestnut Brown, is a brown lake prepared from the horse-chestnut. This now obsolete pigment is transparent and rich in colour, warmer than brown pink, and very durable both in water and oil; in the latter of which it dries moderately well.
268. Iron Browns,
native or artificial, are well represented on the palette, but nothing would be easier than to increase their number. Of all metals, iron is the richest source of colour, capable of affording all colours with the exception of white. None of them, however, are so numerous as the browns, a description of which would fill this chapter. Suffice it to state they are obtainable of every hue, tint, and shade, and are generally permanent. They are made on a large scale and sold under various names for house-painting, &c.