Doublet (lapidary)

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A doublet is a gem made from two layers glued together. It is often used to imitate more expensive stones at a lower cost.

One common type is a garnet-and-glass doublet. It has a thin top layer of natural garnet fused to glass in a chosen color. The color you see comes from the glass, while the garnet’s color isn’t visible. If you look at it in reflected light, you may notice a seam where the two layers join.

A harder garnet makes the stone more durable. For opal doublets, a backing layer of onyx or ironstone (matrix) supports the delicate opal, and can make the overall stone look darker and more valuable.

History: Garnet-and-glass doublets were first used around 1850 after people found that molten glass would stick to garnet. They were a popular way to imitate many gem colors, since the visible color came from the glass. They were produced into the early 1900s, until synthetic gems became common.