PAINTS, DYES, AND VARNISHES 



lime, soda, sulphur plebeian substances in them- 

 selves, that become of such regal importance when 

 combined in the proportions to form the material 

 ultramarine. And now the "Societe d' Encouragement 

 de France" offered a prize of six thousand francs to 

 "anyone who would effect this combination syntheti- 

 cally, and produce ultramarine in wholesale quantities." 

 This prize was soon won (in 1828) by the eminent 

 French chemist, Guimet, who was able to make the 

 pigment on a large scale at a very low price. The exact 

 method used by Guimet was kept secret, and still re- 

 mains so; but as his discovery was followed shortly 

 by the discovery, by several other chemists, of processes 

 leading to similar results, his precise method of proce- 

 dure is of historical importance only. 



At the present time there are two general methods of 

 manufacture, each of which is subject to certain varia- 

 tions. In one of these a mixture of kaolin, soda, 

 charcoal, quartz, resin, etc., is first calcined, forming 

 a green substance known as ultramarine green. To 

 convert this into blue ultramarine a second heating- 

 process with sulphur is necessary. In the other method 

 the process is completed in one heating, and as this 

 also gives the better pigment, it is the one most generally 

 used. Hurst describes one of these methods as follows: 



"A very good mixture to use is 



Kaolin 76 parts 



Sodium carbonate 60 



Sodium sulphate 15 



Sulphur 78 



Charcoal 16 



Diatomaceous earth 18 



Quartz 10 



Resin 12 



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