COLOURS OBTAINED FROM METALLIC OXIDES. 151 



Concerning Greens. 



The greens employed in painting are made with the green Greens j fron* 

 Oxide of copper, or fometimes with a mixture of yellow and copper ' 

 blue. They muft be previoufly melted with their flux ; with- , 

 out this precaution they would become black ; but they do not 

 change after the firft fufion. 



They muft not be treated with a violent fire, or they would not very fixed, 

 totally difappear. The green grounds by ftrong heat are made 

 with the oxides of cobalt and nickel, but it is only a brownifh 

 green. 



The bluifh greens named fky-blue, formerly a colour very Blue-green, 

 much in efteem, can only be ufed on tender porcelain ; they 

 always fcale off from hard porcelain, becaufe there ispotafh in 

 their compofition. 



Thefe greens cannot be ufed on glafs, becaufe they afford a Thefe greens do 

 dirty colour : It is neceffary to put a yellow on one fide and a not f work weil 0R 

 more or lefs pale blue on the other, in order to produce a green. 

 This colour may like wife be fabricated by mixing a blue with Blues for glafs. 

 the yellow oxide of iron. I hope to obtain a green from the 

 oxide of chrome ; and the experiments I have made promife to 

 be attended with fuccefs. The pure chromate of lead, fixed 

 on porcelain by means of a ftrong fire, has already afforded me 

 a very deep and very fixed blue of confiderabfe beauty. 



Concerning Bijires and Brown Reds. 

 Thefe are obtained by mixtures of different proportions of Brown reds from 

 manganefe, brown oxide of copper, and the oxide of iron called ^[^ 0Xlde * 

 umber. They are like wife previoufly fufed with their fol vents, 

 fo that they do not in the lead: change on tender porcelain ; 

 lead not having the fame action on the oxide of manganefe as 

 it has on that of iron. I am convinced of this by an experi- 

 ment fimilar to that I have already related. 



This colour may be employed very well on glafs. ■ Safe* *" 



The brown red grounds by ftrong heat, known by the name Grounds, 

 of fonds caille, are made in the fame manner. Feld-fpar is 

 their flux. There is no titanium in their compofition, though 

 generally aflerted in books. Titanium was not known at Sevres 

 when I firft came to that manufactory. I have treated this 

 lingular metal in various ways, and I never obtained any 

 grounds but a flight obfcure yellow, and very uncertain in its 

 quality. 



Concerning 



