this respect is the pigment "caeruleum" the blue 

 pigment used by the Egyptians, which has resisted the 

 action of time and the elements for several thousand 

 years in many known instances. It is this blue pigment 

 that may still be seen in the ruins of Pompeii, Cairo, 

 and Alexandria; but it is only within the last quarter 

 of a century that its chemical composition has been 

 known. Fouque, the French chemist, found it to be 



Silica (SiO 2 ) 63 . 7 per cent. 



Calcium oxide (CaO) 14. 3 " 



Copper oxide (CuO) 21.3 " 



Ferric oxide (Fe s O) 0.6 " 



It is therefore, probably, a double silicate of copper 

 and calcium, and Fouque believes that the ancients made 

 it by fusing together roasted copper ore with lime and 

 sand. 



THE BROWN MINERAL PIGMENTS 



The brown mineral pigments, constituting a small 

 but important group, are mostly natural pigments. 

 The most important of these is umber, a substance 

 closely resembling the ochres and siennas, but contain- 

 ing more manganese, which is probably the cause of 

 the darker color. The umbers vary in hue from violet 

 brown to reddish brown, and are found in thick mineral 

 deposits in strata sometimes thirty feet in depth. They 

 are found in almost every country, but the finest comes 

 from Cyprus. 



Commercially, umber is marketed in lumps, just as it 

 comes from the mines, or in a powder, which is simply 



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