somewhat hollowed behind (fig. 19), to receive a piece of foil as well as to lessen the depth of colour in very dark stones. Our figures represent the simple cabochon (fig. 17), the double cabochon
 | An image should appear at this position in the text. To use the entire page scan as a placeholder, edit this page and replace "{{missing image}}" with "{{raw image|Handbook of Precious Stones.djvu/46}}". Otherwise, if you are able to provide the image then please do so. For guidance, see Wikisource:Image guidelines and Help:Adding images. |  |
Fig. 19.
| An image should appear at this position in the text. To use the entire page scan as a placeholder, edit this page and replace "{{missing image}}" with "{{raw image|Handbook of Precious Stones.djvu/46}}". Otherwise, if you are able to provide the image then please do so. For guidance, see Wikisource:Image guidelines and Help:Adding images. | |
Fig. 20.
(fig. 18), the hollowed (évidé) cabochon (fig. 19), and the flattened form much used for opals, and called tallow-topped (fig. 20). The double cabochon is usually cut with the base of lesser curvature than the crown; but with many stones a more brilliant play of coloured light within the stone may be secured by reversing these proportions. Although the cabochon form is almost essential to many precious stones, and is useful to hide the poverty and flaws of others, and also is convenient in the case of stones to be used in the decoration of vases and other objects to be handled, yet it ought not to be allowed to displace the various faceted forms. Doubtless there is a quiet beauty and richness in a good cabochon ruby, sapphire, emerald, or jargoon, but we lose some of the most striking characteristics of these gems when we so cut them as not to admit of the display of their dichroism, and their dispersive and reflective powers. The narrow view that all faceted stones are vulgar is based on caprice and ignorance; it is the mere unintelligent whim of a clique of artists and amateur writers on art. For the faceting of the great majority of transparent stones is an operation necessary for the development of those optical qualities upon which the beauty of precious stones mainly depends. It should be performed in strict accordance with certain rules of proportion, which may be deduced from the optical constants of each species of stone.
Information as to the mechanical processes and the materials employed in the cutting and polishing of precious stones may be found in the works of Jannettaz and Dieulafait. Horizontal wheels of steel, gun-metal, copper, lead, pewter, tin and wood
