SCIENCE IN THE INDUSTRIAL WORLD 



The siennas differ very little from the ochres in 

 composition except for the addition of manganese. The 

 quantity of this is so small, however, that it is only recog- 

 nized as a "trace" by the chemists in the analysis, yet 

 this "trace" is sufficient to alter the color. 



An important pigment that is a favorite with some 

 artists on account of its brilliancy, is cadmium yellow, 

 which has the chemical formula CdS. It is permanent 

 and is obtained in several shades of yellow and orange 

 and mixes well with most other pigments. 



Among the yellow mineral pigments that have largely 

 been replaced by some of the foregoing, are the "Mars 

 colors" which were sold in many shades under various 

 names. These colors possess no advantage over the 

 ochres, and have the disadvantage of costing more. 

 Mention has been made above of how the lead pigments, 

 "Turner's yellow" and "Naples yellow," have also 

 yielded to the chromes. The same is true of "King's 

 yellow," which is a bisulphite of mercury. 



Aureolin, a pigment lacking permanency, is still in 

 use. It is a double nitrate of potassium and cobalt, 

 and was at one time very popular with artists. 



SOME BRILLIANT BUT POISONOUS PIGMENTS 



We have seen that the pigments made from lead are 

 poisonous compounds which must be handled with 

 caution, both in the process of manufacture and in the 

 subsequent operations of painting. Far more poison- 

 ous than the lead pigments, however, are those made 

 from the metal mercury, which is the essential constitu- 



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