[859] V. Coloring Materials by Which Gems are Imitated.

Manufacturer and Builder 2, 1874

— The basis of these imitations is a soft white lead glass of highly refracting power, called strass. For imitating topas, glass of antimony, 87 parts, and purple of Cassius, 1 part, is added to 840 parts of strass, or 1 part of crocus martin to 100 of strass. For ruby, the above is fused for 30 hours, or oxid of manganese is used. For emerald, add to 250 parts of strass of verdigris and half a part of crocus mortis. For sapphire, add 1 part of oxid of cobalt to 80 of strass. For amethyst, to 1 pound of strass 20 grains oxid of manganese and 1 of oxid of cobalt. In all cases a careful fusing in furnace or blow-pipe is required of the substances beforehand, well powdered and mixed; but above all, a considerable degree of experience, obtained by continued practice.

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