Enhanced Gems : Types of enhancement

Gem treatments can affect a stone’s value and stability. 

Assembled Stones

Two or three pieces of material can be glued together to make a single assembled stone. Very frequently, treaters form opal cabochons with a thin layer of opal on a secure backing (a doublet), sometimes with an additional clear quartz cover (a triplet). These techniques make use of thin, delicate material, and you can see the layers without magnification.

On the other hand, distinguishing assembled faceted stones can prove more difficult. Inexpensive stones can have colored glue between two layers of colorless, synthetic material. Others are designed to deceive gemologists. They may have tops of natural gem material on a synthetic bottom or a natural but colorless bottom with dyed glue. (Center-fused color treated gems use an HPHT process instead of glue to fuse diffusion-treated pieces).

You can occasionally distinguish doublets by viewing them from the side. However, more often, it takes immersion to distinguish the layers. (Use the immersion procedures for a microscope examination). One of the best indications you're looking at an assembled stone is finding bubbles trapped in the glue layer. (In the pavilion view of the spinel doublet above, those two indistinguishable inclusions are actually bubbles).

Dyeing

Dyes enhance the color of gems. Porous stones, like howlite and lapis lazuli, make ideal candidates for dyeing. However, many crystalline gems, notably quartz and emerald, also receive dyes. Quartz is heated, then quenched, to create thousands of tiny cavities for the dye.

Treaters sometimes add dye to the oil used to fill emeralds and other gems.

Dyed stones typical don't have even color distribution. Look for areas of dark color concentrated in fractures or between grains and fibers.

Fracture Filling

Emeralds are routinely oiled, and the process is occasionally used on other stones. Commonly used fracture fillers include oil, glass, wax, and epoxy.

If the filler has a refractive index close to that of the stone, it allows light to pass through with much less disruption. This gives the appearance of a cleaner stone. Other fillings serve to hide surface imperfections, such as waxing a cabochon. (You can distinguish a wax filling with a hot point test).

To distinguish a liquid filling in a fracture, look for multicolored flashes of light, just as you would see from an oil slick on a wet street. This requires the light to hit the filled fracture at the correct angle, so use the oblique lighting technique.

At times, many unfilled fractures will also show iridescent colors. However, they always stand out in high relief.

If the oil has been colored, you'll also see dye concentrations, as described above.

Old treatments dry out and leave a dendritic pattern in the fractures. This is easy to spot with substage lighting.

Laser Drilling

This process involves drilling holes with lasers to reach inclusions, then introducing acid through the holes to dissolve the inclusions. This creates a cleaner gemstone.

Diamonds commonly receive this treatment, but it's also used occasionally on emeralds, rubies, and other gems. The cleaner appearance of laser-drilled stones increases their value. However, they're not as valuable as untreated stones of similar clarity. Therefore, you need to look for laser drill holes and note them in any gemstone report or appraisal.

Surface Coating

Gems can receive a wide variety of coatings to enhance their color. Mystic topaz is perhaps the most well-known example of this type of enhanced gem.

You can find many different types of materials used for surface coatings — micro-thin platings, plastics, and even foil. However, all these coatings have the same telltale sign: they can show wear. Look for areas on the gem surface where the coating has chipped off, especially on the facet edges.