Online Encyclopedia

GROUP III

Online Encyclopedia
Originally appearing in Volume V21, Page 598 of the 1911 Encyclopedia Britannica.
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GROUP III. Sulphides.—Some of the members of this group are liable to contain free sulphur, and some may give up this element to the metallic bases of other pigments. Thus cadmium yellow blackens emerald green, producing copper sulphide. Another pigment of this group, vermilion, is prone to a molecular change whereby the red form passes into the black variety. This change, frequent in water-colour drawings, is scarcely observable in works painted in oil. The sulphides comprise cadmium yellow (CdS), king's yellow (As2S2), realgar (As2S,), antimony, red (Sb2S3) and vermilion (HgS). It is convenient to give places in the same group to the various kinds of ultramarine, blue, green, red, violet and native, for in all of them a part of the sulphur present occurs in the form of a sulphide. It may be stated that the sulphides of arsenic and antimony just named are dangerous and changeable pigments not suited for artistic painting.
End of Article: GROUP III
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