A superior glass containing oxide lead used for jewelry to imitate gems and gemstones. Joseph Strass perfected paste, although paste was used since ancient times as imitations of precious stones. Much paste is actually a composition of pounded rock crystal melted with alkaline salts and colored with metallic oxides.
Some paste stones are set with bright foil, a thin leaf of metal placed in back of a glass stone to heighten its brilliance.
The finest quality paste, however, requires no foil or backing and is usually claw-set or bezel mounted as if it were the genuine article. Inferior paste may be backed with mercury or quicksilver and applied by machine rather than the more expensive handwork which requires each, paste stone to be individually mounted. Commercial pastes are molded. Unless one is an expert, the superior pastes of today are sometimes difficult to distinguish between diamonds, spinels, or other imitated gems.