Bright opal triplet brooch in sterling silver. 57x15mm. An opal triplet is a manufactured opal consisting of three layers. A paper-thin slice of solid natural transparent or translucent-coloured opal is glued to a dark backing of black glass, with a dome of clear quartz crystal glued onto the top. The crystal dome is to magnify and protect the opal. A triplet is less expensive than a doublet as less opal is used.