714 CAMEOS. 



li^ht, the amorplious are translucent, grayish, and curiously per- 

 meable by liquids. In consequence of their permeability certain 

 colors are sometimes naturally acquired by the amorphous laj^ers of 

 clialcedony. In cases where the water of infiltration is loaded with 

 iron a yellowish red will probably be found, producing what is 

 called a sardonyx, from a Persian word " zard," meaning yellow. 

 Other metals will impart other tints. 



Pliny (first century'), in his Natural History, among other notes 

 concerning jewels, says that (Book xxxvii) in his hands are 

 books " Avherein it is deciphered how to sopliisticate transparent 

 gems,'' a statement which likely enough refers to artificial coloring 

 of chalcedony. But at the same time it may also only mean the 

 paste imitations which were plentifully made both before and dur- 

 ing the time the Natural History was written. 



It is, I think, probably due to the discovery of the remarkable 

 adaptability of the onyx stone for cameo work that the art has 

 developed so as to become one of a considerj^ble range and consider- 

 able importance both from the anticpuirian and the artistic point 

 of view. 



Without this discovery we should not have possessed the Strozzi 

 Augustus of the British Museum, or the Portland vase, or any of 

 the works like them, bearing designs cut in one colored layer on a 

 background of another, but we might have had the vase of St. 

 Martin cut simply in an agate without any reference to the trend of 

 its color layers, and the phalerae in chalcedony or amethyst, or any 

 other stone of one color. But without the onyx cameos it is likely 

 enough that all the rest would never have been considered more tlian 

 small and delicate pieces of sculpture, not belonging to a school o 

 their own, so that for the existence of cameos as a distinct branch 

 of art we are probably indebted particularly to that unknown 

 lapidary who first hit upon the idea of cutting the V)anded onyx 

 parallel to its color layers instead of across them. 



At Oberstein, in Oldenburg, there is a large onyx industry, origi- 

 nally fixed there because the stone was found plentifully in the 

 neighborhood, but this supply having now become comparativelv 

 small, onyxes are sent there in quantities from India, Brazil, or 

 Egypt to be sliced up ready for cutting, shaped, and artificially 

 stained with colors as may be desiral)le. 



The staining of onyx is well understood and is now reduced almost 

 to a certainty, so that it is said that any ancient and i)resumably 

 natural tint can be arlificially produced with great accuracy: 



Reds by means of ])ernitrate of iron. 



Black by oil, honey, en- sugar. 



Blues by iron with ferrocyanide of potassium (prussian blue). 



Greens bv nitrate of niclcel. 



