152 



COLOURS OBTAINED EROM METALLIC OXIDES. 



Blacks; 



Oxides for com 

 pofing black. 



Fine black at 

 5lvres> 



for glafs* 



Mixtures of co- 

 lour* 



Recapitulation. 



Unchangeable 

 fpecimens. 



Concerning the Blacks. 



Black colours are the mofl difficult to be obtained very beau- 

 tiful. There is no metallic oxide that fingly affords a fine 

 black. Manganefe gives the Deft. Iron an opaque, dull, 

 Wittered black, which eafily turns to red ; the makers of co- 

 lours have therefore combined feveral metallic oxides which 

 fingly do not afford blacks, and they have obtained a very 

 beautiful colour, but it is fubject tofcale and become dull. 



Thefe oxides are thofe of manganefe, the brown oxides of 

 copper, and a little of that of cobalt. Grey is obtained by 

 fuppreiTing the copper and increafing the quantity of flux. 



The Sevres manufactory is* the only one which has as yet 

 produced beautiful blacks with a fixong fire. This is more 

 owing to the quality of the bifcuit than to any peculiarity of 

 procefs. It is by a mixture of blue with the oxides of manga- 

 nefe and iron, that they make this very brilliant black. 



The blacks for opaque glaffes are made the fame as for paint- 

 ing, by giving different dofes of folvent, 



I have (hewn the principles of fabricating each principal co- 

 lour : it is clear that by mixing thefe colours together, all pof- 

 fible fhades may be obtained : and alfo, that care in the prepa- 

 ration, choice of materials, and jult proportions of dofes, muft 

 exhibit very fen fible differences to the experienced eye of a 

 painter. A knowledge of the compofition of colours does not 

 give the requifite care and neatnefs in making them up. 



On recapitulating the fa6ls I have juft fiated, in order to 

 prefent them in a general view, we fee,/?r/?, that amongft the 

 colours ufually employed for hard porcelain, one only is fuf- 

 ceptible of change ; namely, the carmine ; and this may be 

 replaced by the reds of iron, and then no colour changes. 



I have prefented to the Infiitute an unbaked head made in 

 this manner, and a painting of two rofes, the one baked, the 

 other in its firft fiate. There was not any difference between 

 them. 



Secondly, That amongft the colours of foft porcelain and 

 enamel feveral change confiderably, particularly the reds of 

 iron and gold with the yellows, greens, and browns. None 

 Jiave been fubftituted inftead of them, this fpecies of painting 

 being almoft abandoned. 



Thirdly^ 



