1084 VITRIFIABLE PIGMENTS 



moist, upon the glass plate with 10-5 grammes of a lead-glass obtained by fusing 4 

 parts of minium with 1 of quartz-sand, drying it slowly in the manner above men- 

 tioned, and then reducing it to a fine powder upon the glass plate. When the pigment 

 is burnt-iu at a lower temperature, a larger addition of lead-glass is required. This 

 blue-violet pigment is more especially adapted for mixing with blue pigments. _ It is 

 not applicable to glass-painting. The most important requisite in the preparation of 

 good purple and violet vitrifiable pigment is the very minute state of division of the 

 gold in the gold precipitate, and of the latter in the lead-glass, which is accomplished 

 by mixing the moist precipitate with the glass. 



By mixing the light purple with the dark purple or with the red-violet, or the red- 

 violet with the dark purple, in different proportions, the artist is able to produce every 

 possible tint of purple and violet. The light purple, without any additional silver, 

 furnishes an amaranth-red colour, like that seen upon the porcelains of the pre- 

 ceding century, when the peculiar property of silver, of converting the amaranth- 

 red into a rose-red colour, does not appear to have been known. Dr. Richter, who 

 at the commencement of this century prepared the pigments for the Royal Berlin 

 manufactory of porcelain, appears, however, to have employed it for his purple, as a 

 very beautiful rose colour may be seen upon the painted porcelain of that time. 



Pink. One gramme of gold is dissolved in nitromuriatic acid ; the solution mixed 

 with one of 50 grammes of alum in 20 litres of spring water ; then mixed, constantly 

 agitating, with T5 gramme solution of protochloride of tin of 1700 spec, grav., and 

 so much ammonia added until all the alumina is precipitated. When the precipitate 

 has subsided, the supernatant liquid is poured off, and replaced about 10 times suc- 

 cessively by an equal amount of fresh spring water; the precipitate is then collected 

 on a filter, and dried at a gentle heat. It weighs about 13'5 grammes ; and to pre- 

 pare the pigment is mixed with 2'5 grammes carbonate of silver, and 70 grammes of 

 the same lead-glass, described under light purple (2 minium, 1 quartz-sand, 1 calcined 

 borax), and reduced to a fine powdei* on the glass plate. 



This colour is adapted only for the production of alight pink ground upon porcelain, 

 and must only be applied in a thin layer ; when laid on in a thick layer the gold 

 separates in a metallic state, and no colour is produced. 



All the gold colours above described do not furnish, when fused alone in a crucible, 

 red or violet glasses, as might be expected, but dirty brow'n or yellowish glasses, which 

 appear troubled from the separation of metallic gold and silver ; this peculiar beauti- 

 ful tint is only developed when they are fused upon the porcelain glaze in a layer, 

 which must not be too thick; they then colour it through and through, as a piece of 

 porcelain painted with it shows distinctly in the fracture. If the layer exceeds a 

 certain thickness, the gold and silver separate in a metallic state ; and they produce 

 either a liver colour, as for instance the purple and violet pigments, or no colour at all, 

 as is the case with the more fusible pink pigment. 



Yellow Pigments for painting upon Porcelain. The yellow vitrifiable pigments are 

 lead-glasses, coloured either by antimonic acid or oxide of uranium. The antimoniate 

 of potash is prepared by igniting 1 part of finely-powdered metallic antimony with 

 2 parts of nitre, in a red-hot Hessian crucible, and washing the residue with water. 

 The oxide of uranium is obtained in the fittest state, by heating the nitrate, until the 

 whole of the nitric acid is expelled. 



Lemon Yellow. 8 parts of antimoniate of potash, 2 parts of oxide of zinc, 36 parts 

 of lead-glass (prepared by fusing together 6 parts minium, 2 parts of white sand, and 

 1 part of calcined borax), are intimately mixed, and heated to redness in a porcelain 

 crucible, which is placed in a Hessian crucible, until the mixture forms a paste ; it is 

 fchen taken out with a spatula, pounded after cooling, and ground upon a plate glass. 

 If the pigment is fused longer than requisite for the perfect union of the ingredients, 

 the yellow colour is converted into a dirty grey by the destruction of the antimoniate 

 of load. 



Light Yellow. 4 parts of antimoniate of potash, 1 part of oxide of zinc, and 36 parts 

 of lead-glass (prepared by fusing together 8 parts of minium and 1 part of white sand), 

 are well mixed, fused in a Hessian crucible, and after cooling, pounded and ground. 

 In the preparation of this colour, long fusion is less injurious than with the preceding 

 one, owing to the absence of the borate of soda in the lead-glass. The colour itself is 

 more intensely yellow than the preceding one, and is extremely well adapted for 

 mixing with red and brown pigments ; but it does not furnish such pure tints as 

 that when mixed with green ; owing to its higher specific gravity, it flows more 

 freely from the brush, and may bo laid on in a thicker layer, without scaling off after 

 the firing. 



Dark Yellow, 1. 48 parts minium, 16 parts sand, 8 calcined borax, 16 antimoniate 

 of potash, 4 oxide of zinc, and 6 parts peroxide of iron (caput mortuum}, arc intimately 

 mixed and fused in a Hessian crucible, until the ingredients have perfectly combined, 



