Professional Gemologist Certification Course
Gemstone Coatings: CVD and More
Gemstone Coatings for Luster and Brilliance
Coatings are added layers to gemstones that can vary widely in form and function. One of the oldest and most common gemstone coatings is wax. A layer of wax can improve luster and protect porous gems from oils in the wearer’s skin. This type of enhancement is common in cabbed gems — like turquoise, lapis lazuli, and jade — and is also routine for pearls.
In some cases, instead of a natural wax, an artificial polymer or lacquer coats the gem. Typically, the gem dealer will choose a polymer coating to harden the surface of crumbly or especially soft gems. Polymer coatings are most common in inexpensive turquoise but are also occasionally used for pearls, amber, and coral.
Foil backings to enhance brilliance were once quite popular. However, abundant and inexpensive synthetics like cubic zirconia have largely replaced rhinestones.
Detecting Colorless Gem Coatings
Colorless coatings can be difficult to detect without destructive techniques. However, you can sometimes see an uneven layer of lacquer or polymer under a loupe or microscope. In older gems, the coating may have chips or scratches.
If you suspect a coating but can’t find chips or…
Addison Rice
A geologist, environmental engineer and Caltech graduate, Addison’s interest in the mesmerizing and beautiful results of earth’s geological processes began in her elementary school’s environmental club. When she isn’t writing about gems and minerals, Addison spends winters studying ancient climates in Iceland and summers hiking the Colorado Rockies.
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