1088 VITBIFIABLE PIGMENTS 



To hit this point exactly when the oxide of iron has assumed the desired carmine 

 tint is not so easy, as it changes very rapidly at these temperatures. 



The pigment is prepared by mixing 2 parts of the purple-coloured peroxide of iron 

 with 5 p;irts of lead-glass, obtained by fusing together 5 parts of minium, 2 parts of 

 sand, and 1 part of calcined borax. 



Chestnut Brown. This colour of various shades, even to black, is acquired by the 

 peroxide of iron, at still higher degrees of heat than required for the preparation of 

 red colours ; the pigments are prepared by mixing 2 parts of the chestnut-brown per- 

 oxide of iron with 5 parts of lead-glass, prepared by fusing together 12 parts of minium, 

 8 parts of sand, and 1 part of calcined borax. 



Chamois, 1 part of the hydrate of the peroxide of iron, prepared by precipitating 

 the peroxide of iron with ammonia is mixed with 4 parts of the lead-glass, described 

 in the preceding, and the mixture ground fine on a plate of glass. This colour is laid 

 on very thin, and serves to produce a yellowish-brown ground. 



Flesh Colour. 1 part of peroxide of iron, 4 parts of dark yellow 2, and 10 parts of 

 lead-glass, prepared as described under chestnut-brown, are well mixed and ground 

 fine upon a plate of glass. This colour can also only be employed in a thin layer. 

 Various tints may be given to it by mixing it with a red peroxide of iron, sky-blue, 

 or dark yellow 2. The red of the cheeks and lips are painted upon it with Pompadour- 

 red. 



When the above colours are burnt-in upon porcelain, it is distinctly seen under the 

 microscope that the peroxide of iron is suspended unaltered in the clear lead-glass ; at 

 least the quantity dissolved by the fused lead-glass is so small that it is not perceptibly 

 coloured. 



Various Brown Pigments for painting upon Porcelain. Light Brown, 1. 6 parts of 

 dry protosulphate of iron, 4 parts of dry sulphate of zinc, and 13 parts of nitre are well 

 mixed, and heated to a redness in a Hessian crucible, until the whole of the nitre is 

 decomposed. When cold, the crucible is broken, the residue removed, and separated 

 by boiling with water from soluble matters. A yellowish-brown powder remains, which 

 is a combination of oxide of zinc with peroxide of iron. The pigment is made by 

 mixing 2 parts of this compound with 5 parts of lead-glass, prepared by fusing to- 

 gether 12 parts of minium, 3 parts of sand, and 1 part of calcined borax. 



Light Brown, 2. 2 parts of dry sulphate of iron, 2 parts of dry sulphate of zinc, 

 and 5 parts of nitre, are treated in the same manner as described for light brown 1. 

 The resulting compound of oxide of zinc and iron is of a lighter tint ; the pigment is 

 prepared from it as above. 



Light Brown, 3. 1 part of dry sulphate of iron, 2 parts of dry sulphate of zinc, and 

 4 parts of nitre are treated as directed for 1 and 2. 



The light brown colours, after having been burnt-in upon porcelain, exhibited, under 

 the microscope, the transparent particles of the yellowish oxide of iron and zinc sus- 

 pended in the colourless lead-glass. 



Bistre Brown, 1. 1 part dry sulphate of manganese, 8 parts of dry sulphate of zinc, 

 12 parts dry sulphate of iron, and 26 parts nitre, are treated as directed for light 

 brown 1, and the resulting dark brown powder (a combination of the oxides of zinc, 

 iron, and manganese), mixed with 2 times its weight of lead-glass of the same compo- 

 sition as for light brown 1. 



Bistre Brown, 2. 1 part dry sulphate of manganese, 4 parts dry sxilphate of iron, 4 

 parts dry sulphate of zinc, 12 parts nitre, are treated as for bistre brown 1. The colour 

 is somewhat darker. 



Sepia Brown, 1. 1 part dry sulphate of iron, 1 part dry sulphate of manganese, 2 

 parts dry sulphate of zinc, and 5 parts nitre, are treated as directed for light brown 1, 

 and the greyish-brown pigment thus obtained mixed with 2| times its weight of lead- 

 glass of the above composition. 



Sepia Brown, 2. 1 part calcined sulphate of iron, 2 parts calcined sulphate of man- 

 ganese, 6 parts calcined sulphate of zinc, and 10 parts nitre, are treated as for sepia 1. 



Dark Brown. 1 part dry sulphate of cobalt, 4 parts dry sulphate of zinc, 4 parts 

 dry sulphate of iron, and 10 parts of nitre, are mixed and treated as directed for light 

 brown 1. The resulting beautiful dark reddish-brown combination of the oxides of 

 cobalt, zinc, and iron is mixed with 2J times its weight of the same lead-glass as for 

 the preceding colours. 



Chrome Brown. 1 part, of hydrated peroxide of iron is intimately mixed with 2 parts 

 of the chromate of the protoxide of mercury, and then heated to redness in a dish, in 

 an open muffle, to expel the whole of the mercury. The dark reddish-brown compound 

 of the oxides of chromium and iron is mixed with 3 times its weight of lead-glass, 

 prepared by fusing together 5 parts of minium, 2 parts of sand, and 1 part of calcined 

 borax. 



When examined under the microscope, after being burnt-iu upon porcelain, these 



