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Georgian Foil Backed Quartz Pendant.
Photo Courtesy of Lang Antiques.

Foiling is the backing of a gemstone with a metallic or non-metallic sheet to improve its optical performance. The foil acts both a reflector as well as a coloring agent. Many jewels that survived carried diamonds and gemstones that were treated in this manner. Almost always these stones were set in silver closed backs to shield the foil from deteriorating.

See Also: Gemstone Surface Enhancements