Step 2: Advanced Gemology
It is common to glue two or three pieces of material together to make a single stone. Opals are frequently formed as doublets, a thin layer of opal on a secure backing, or triplets, with a clear quartz cover. This is done to make use of thin, delicate material and the layers are visible without magnification.
Assembled, faceted stones are more difficult to distinguish. Inexpensive stones use colored glue between two layers of colorless, …
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