Prussian Brown

This pigment, as usually met with in commerce, contains a considerable quantity of a soluble salt of potash, and is not fitted for the use of artists. But this impurity need not be present, as it may be removed by a thorough washing of the powdered colour with boiling water. A still better plan is to prepare Prussian brown from one of those varieties of Prussian blue which contain no potassium. It is made by throwing small pieces (the size of hazel-nuts) of Prussian blue upon a plate of iron maintained at a red heat. Each fragment burns like tinder, and if care be taken to employ the right heat for the proper time, will show a mixed hue, partly yellowish brown, partly reddish brown, and partly black. The product, still hot, is thrown into water, ground, washed, and dried. Prussian brown thus made has a rich colour of considerable translucency and good drying character. In hue it is warmer than asphalt. It is quite permanent.