X^" Rifearchcs rcfpeSling tM 



a little the fliadcs. I have already pointed out the metliGO ' 

 of employing thefe oxyds on raw enamel : were not that 

 method only followed in this cafe, the oxyd of copper would 

 extend, and fpread itfelf; like a cloud, beyond the limits pre- 

 fcribcd for it. 



A niixturt' of vcllow and blue is alfo ufed to produce green; 

 Thofe who paint figures or portraits employ glafs conipofed 

 in this manner J but ihofe who paint glazed veflels, either 

 earlhcn-ware or porcelain, employ in general copper green. 



Independently of the beautiful green colour produced by 

 oxydated copper, it produces alfo a very beautiful red colour; 

 but I do not know that it is e^Bployed on enamel. This 

 beautiful red colour, produced by copper, Is exceedingly fugi- 

 tive. The oxyd of copper gives red only when it contains 

 very little oxygen, and approaches near to the ftate of a re- 

 gulus, Notwilhiianding the difficulty of employing this oxyd 

 for a red colour, a method has been found. to (lain tranfparcnt 

 glafs with different fliades of a very beautiful red colour by 

 means of calx of copper. The procefs is as follows : You- 

 do not employ the calx of copper pure, but add to it calx of 

 iron, which for that purpofe muft not be too much calcined j 

 you add ajfo a very fmall quantity of calx of copper to the 

 mafs of glafs Vvhich you are defn'ous of tingeing. This glafs 

 at fill nuiit have only a very flight tinge of green, inclining 

 to yellow, AVhcn the glafs has that colour vou-niake it pafs 

 to red, and even a very dark red, by mixing.w ith.it red tartar 

 in powder, and even tallow. You muft mix this matter well 

 in the glafs, and it will allume a very dark red colour. The 

 glafs fvvelh.; up very much by this addiiion. JJefore it is 

 worked, it muft be fuiTered to fettle, and become compadlj 

 but as foon as it hft$ fully alTumed the colour it muft be im- 

 mediately worked, for the, colour does not remain long, and 

 even often difappears while working; but it may be reftored 

 by heating the glafs at'the flame of a lamp. It is exceedingly 

 • difficult to make this colour well ; but when it fucceeds it is 

 very beautiful, and has a great deal of fplendour. By em-i 

 ploying, the calx of copper alone for the procefl'es above men- 

 tioned you will obtain, when you fuccecd well, a red fimilar 

 to the moft beautiful carmine. The calx of iron changes 



the 



