Step 2: Advanced Gemology

Lesson 5

gemstone enhancements - irradiated topaz

“Topaz,” irradiated, from Pakistan. © Rob Lavinsky, Used with permission.

Gemstone enhancements are procedures applied to gems to improve their appearance and wearability. There are many kinds of treatments. Some have been used for centuries, while others are recent. People in the gem industry choose treatments based on the gem type and the desired effect. Although some gemstone enhancements are commonplace, the gem-buying public remains relatively unaware of these practices. However, this age of information and disclosure is bringing changes.

Some in the gem industry feel too much information will confuse customers and hurt sales. For example, some procedures involve subjects such as the physics of light response to molecular structure. They argue that there’s no need to disclose treatments that are indistinguishable from natural gem formation processes. Others in the industry feel the public’s right to know outweighs these concerns.

The topic of gemstone enhancements is controversial and vast. So, as an introduction, here are the most common procedures you’ll likely encounter in the world of gems.


Natural Gems and Enhanced Gems

First, let me clarify some terms.

  • Natural gems form in the earth. Treatments after mining don’t change their status as natural gems.
  • Synthetic gems are made under lab conditions that mimic natural formation processes, only greatly accelerated.

Treatments or enhancements occur after the gems are formed. Thus, an enhanced gemstone isn’t necessarily a synthetic stone.

Common Gemstone Enhancements

Heat Treating

The most common form of enhancement is heating. For example, jewelers should inform their customers that rubies and sapphires are “probably heat treated,” since heating is so common for corundum gems.

“Probably” doesn’t sound very professional. However, heating enhancement so closely resembles what happens in nature that you can’t always tell if gems have been treated after mining. Sometimes, microscopic examinations can reveal evidence of heating. Otherwise, there is no way to tell if the heating was done before or after mining.

(Again, let me clarify. Heat is one of the conditions that cause gems to form, whether in the ground or in a lab. Heating that occurs during gem formation isn’t an enhancement. On the other hand, heating applied after gem formation is considered an enhancement).

Another often heat-treated gem is aquamarine. Most of this material has a natural green tint. If heated properly after mining, these gems may turn pure blue. However, sometimes aquamarines do come out of the ground a pure blue. Natural heating underground and artificial heating after mining can produce identical results. For this reason, jewelers should describe any pure blue aquamarine as “probably heat treated.”

gemstone enhancements - untreated aquamarine

“Beryl (Var: Aquamarine),” from Minas Gerais, Southeast Region, Brazil. © Rob Lavinsky, Used with permission.


Yes, radiation. (Now you know why some in the gem industry are nervous about full disclosure). Radiation is a scary word. Revealing that a gem was irradiated will likely drive away customers. But just as with heating, radiation enhancements duplicate what happens in nature. During their formation, radioactive elements affect many gem crystals. That doesn’t mean these gems are radioactive or otherwise harmful.

Most blue topaz gems are colorized in a two-step enhancement process. First, radiation modifies electron sharing between certain atoms in the crystal structure of colorless topaz. This turns the topaz brown. Next, heating creates a stable blue color.


Some gems, notably emeralds, have internal fractures. Light reflection off their surfaces seriously affects the clarity and brilliance of these stones. Simply filling these fractures with a substance with similar optical properties makes these tiny cavities transparent. The difference in the appearance of the finished gem can often be startling!

Unlike heat and radiation, oiling gemstones doesn’t mimic a process that occurs in nature. To gem cutters, oiling poses a serious problem, because those tiny fractures represent structural weaknesses. They must consider these areas in the cutting process. Oil-masked fractures increase the risk of damaging a gem during cutting. To gem owners, oiling is well worthwhile. The oil filler isn’t visible. It simply allows the natural beauty of the stone to shine. For them, gemstone enhancements like oiling increase both the emotional and monetary value of the gem.

Jewelers should tell buyers that oiled gems need special care. For example, frequently washing dishes while wearing such a stone can make it less brilliant. Vigorous cleaning methods, like using heat or an ultrasonic system, can be disastrous.

Dyeing and Sealing

Gemstone enhancements can be applied to less expensive gems, too. Dyes are common treatments for stones such black onyx. Jewelers often seal porous materials like turquoise with surface coatings, such as paraffin wax, so body oils won’t cause discoloration.


Diamonds, rubies, and sapphires can be filled with lead glass to improve their clarity.

gemstone enhancements - dyeing

“Black Onyx” by Grandor. Licensed under CC By-SA 3.0.