nnS. fixed by Fujion on different vitreous Bodies. 23 



Thefe oxides are thofe of manganefe, the brown oxides of 

 copper, and a little of the oxide of cobalt. The gray is ob- 

 tained by fiipprefling the copper, and increafing tne dofe of 

 the Htix. 



The manufaftory of Sevres is the onlv one which has hi- 

 therto produced beaiuifid blacks in a lirong heat. This is 

 owing rather to the quality of its palte than to any peculiar 

 procelfes, fince it docs not conceal ihtni. It is by darkening 

 the blue by the oxides of manganefe and iron tbat they are 

 able in that, manufaclory to obtain very brilliant blacks. 



Having here made known the principles of the fabrication 

 of each principal colour, it may be readily conceived that 

 by mixing thefe colours together all the fhades polfible may- 

 be obtained. It is evident alfo that care in the preparation, 

 choice in the raw materials, and a jidl proportion of dofes, 

 mart produce in the refults differences very fenfible to an eye 

 accu(i:omed to painting. A mere knowledge of the compofi- 

 tion of the colours does not give the talent of executing them 

 well. 



In recapitulating the fafts above mentioned, to prefeut 

 them under another general point of view, it is feen : 



ift, That among colours generally employed on hard 

 porcelain one only is fufceptible of changing, viz. carmine, 

 and the tints into which it enteis : that its place may be 

 fupplied by the reds of iron, and that no colour then changes, 



I have prcfented to the Inititute a head not baked, exe- 

 cuted according to this method; and the painting of two 

 roles, that of the one baked, and that of the other not baked. 

 It has been feen that there was no difference between them. 



2d, That among the colours for foft porcelain and enamel, 

 feveral change in a confiderable degree. Thefe are princi- 



tially the reds of gold and iron, the yellows, tlie greens, the 

 )rowns. They have not been replaced by others, becaufc 

 this kind of painting has been almolt abandoned. 



3d, That feveral of the colours on glafs change alfo by 

 acquiring comi)lcle tranfparcncy. Thefe in j)arlicular are 

 the yellows and greens. 



4th, Thai it is neither by calcining the colours in 3 higher 

 degree, nor previoufly fufmg them, as fujjpofcd by iume, 

 that they are prevented from changing, lince thefe nieans 

 really alter the changing colours, and produce no efi'e<5l on 

 the reQ. The change wliich leveral colours experience on 

 foft porcelain and on glafs docs not then depend on the na- 

 ture «)f their compoliiit)n, but rather on that of the body on 

 which they are applied. 



B ^ Confc- 



