Gem treatments are human-made improvements to the appearance of gems after they are mined.  Treatments generally seek to improve the color, clarity, or both of the gem.  Gem dealers often use treatments to improve gems that would otherwise be unsallable, or to get more money for sellable material.  Gemstone treatments have been common place for over one hundred years.  This may surprise some of you, but it’s true.  With today’s cutting-edge technology, treatments are more common than ever.  Let’s have a brief discussion about treatments of some of the colored gemstones you will see in typical jewelry stores.

Diamonds:

Diamonds can be treated to improve the clarity by filling fractures or by laser drilling and subsequent bleaching of dark inclusions.  For more detail, please see our article "How to Save Money with Clarity-Enhanced Diamonds."  Additionally, new high-tech, high-temperature and high-pressure treatments can also improve or create new colors.

Rubies and sapphires:

I group these gems together because they are the same mineral, corundum.  The treatments are almost identical.  Rubies and sapphires are almost always heat treated at high temperature which enhances the color and can also improve the clarity.  This treatment is considered usual and customary and is therefore not typically disclosed to buyers.  However, a fine-quality ruby or sapphire, with a lab report stating no heat treatment has been used, is sold at a premium.  Another common treatment is diffusion, where a coloring agent (usually titanium in blue sapphires or beryllium in orange sapphires) is introduced during the heating process and diffuses into the gem, enhancing its color.  This type of treatment should be disclosed by the dealer so the customer knows what they are getting.

Emeralds:

Emeralds are typically filled with materials that improve clarity (hide flaws.)  It used to be various oils, but now high-tech resins, similar to epoxy, are used.  Once again, some treatment is expected, but, if it is extensive, that fact should be disclosed to a potential buyer.  A fine emerald with a report stating no treatment is sold at a premium.

Aquamarine:

Aquamarine is the same mineral as emerald but has very different characteristics. Aquas are routinely heat treated to remove the green component from them.

Tanzanite:

Tanzanite is typically heated to change the color from greenish brown to violet or blue.

Amethyst and Citrine:

Once again, these are the same mineral.  Heat treating changes amethyst to citrine, lightens the color in amethyst, or creates ametrine from amethyst.

There are many other gemstones that have treatments, so it’s a good idea to ask the gemologist at your jeweler which treatments have been done to the gems you are looking at.

Matt Dendel
Geologist, GIA

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