ENAMELLING 



fers little from it, as well as the shades 

 which are obtained from their mixture 

 with other colours, really change in all 

 porcelains, and in the hands of all opera- 

 tors. But this is the only one which 

 changes on hard porcelain. It may be 

 replaced by a substitution of rose-co- 

 lour from iron, which does not change ; 

 so that by excluding from the pallet the 

 carmine made from gold, and substitut- 

 ing the rose-coloured oxide of iron here 

 spoken of, we have a pallet composed of 

 colours, none of which are subject 10 any 

 remarkable change. The rose-coloured 

 oxide of iron has been long known, but 

 was not employed on enamel, because it 

 is then subject to considerable change. 

 Or, perhaps, when the painters on ena- 

 mel became painters on porcelain, they 

 continued to work according to their an- 

 cient method. 



It might be supposed, that by previous- 

 ly reducing the colour flamed carmine, 

 already mixed with its solvent into a 

 vitreous matter, the last tint would be 

 obtained; but the fire which must be 

 used to melt this vitreous mass destroys 

 the red colour. Besides, it is found, that, 

 to obtain this colour in perfection, it is 

 necessary to pass it through the fire as 

 little as possible. 



The carmine of tender porcelain is 

 made of fulminating gold, gently decom- 

 posed, and muriate of silver ; there is no 

 tin in it, which proves it is not necessary, 

 for the fabrication of a purple colour, 

 that the oxide of this last metal and that 

 of gold should be combined. 



Violet is likewise obtained from the 

 purple oxide of gold. This colour pro- 

 ceeds from having a greater quantity of 

 lead in the flux, and it is nearly of the 

 same tint, whether crude or baked. 



These three colours totally disappear 

 in the strong fire necessary to bake por- 

 celain. 



Carmine and purple afforded, upon 

 glass, only tints of dirty violet. The vio- 

 let, on the contrary, has a beautiful ef- 

 fect, but is subject to change to blue. 



Concerning the Red, Rose, and JJrmvn 

 Colours, obtained from Iron. 



These colours are made from red 

 ozydated iron, prepared with nitric 

 acid. The oxides are calcined still more 

 by exposing them to the action of fire. 

 If too much heated, they change to a 

 brown. 



Their flux is composed of borax and 

 minium in small quantity. 



These are the oxides which afford the 

 rose and red colours, which may be sub- 

 stituted instead of the same colours made 

 from oxide of gold. If properly applied 

 on hard porcelain, they never change. 

 Brougman made roses with these colours, 

 and there was no difference between the 

 flower, before and after baking, except 

 the brilliancy which colours naturally 

 receive from fusion. 



The colours may either be previously 

 fused or not, at pleasure. 



In a violent fire, they either partly 

 disappear, or produce a dull and brick- 

 dust red colour, which is not at all agree- 

 able. 



Their composition is the same, either 

 for tender porcelain or for glass. They 

 do not change on the latter, but on the 

 former they almost entirely disappear 

 by the first fire; and they must be laid 

 on very heavily, in order to have any 

 part visible. 



It is to the presence of lead in their 

 glaze that this singular effect must be at- 

 tributed. Brougman ascertained this 

 by a very simple experiment. He placed 

 this colour on window glass, and fired 

 it very strongly., and it did not change . 

 He then covered some parts of it with 

 minium, and again exposed it to the fire. 

 The colours totally disappeared in those 

 places where the red oxide of lead had 

 been applied. When this experiment 

 was performed on a larger scale, in a 

 closed vessel, a large quantity of oxy- 

 gen gas was disengaged. 



This observation seems clearly to 

 prove the effect of oxydatedlead as a dis- 

 colourer of glass. We see that it does 

 not operate, as has been supposed, by 

 burning combustible impurities in the 

 glass, but by dissolving, discolouring, 

 and volatilizing the oxide of iron, which 

 may affect its clearness. 



Concerning the Yellotvs. 



Yellows are colours which require 

 much precaution in fabricating, on ac- 

 count of the lead they contain ; which, 

 sometimes, by approaching to the metal- 

 lic state, produces black spots. 



The yellows of hard and tender porce- 

 lain are the same. They are composed of 

 oxide of lead, white oxide of antimony, 

 and sand. Oxide of tin is sometimes 

 added; and when it is required very 

 lively, and resembling the colour of mari- 

 gold, red oxide of iron is added, the very 

 deep colour of which disappears during: 

 the previous fusion they undergo, on ac- 



