The Earth is very hot–over 10000 degrees Fahrenheit at its core.  Over the millions of years that gemstones formed in the earth, some have been subjected to high temperatures.  Interestingly enough, this heat can alter the light absorption of the stone, changing its color.  Sometimes heat “improves” the color of the stone, perhaps taking a gray, brown, or almost colorless stone and turning it to a cheerful blue or a regal purple.

Man has found a way to heat stones that Earth neglected to heat.  The most common types of heat treated gemstones are ruby, sapphire, topaz, tanzanite, and zircon.  If you buy one of these stones, you can be quite certain that it’s been heated by man.  You’d pay a huge premium to have beautiful color without man-made heat.  The time spent heating, the temperature, and the other treatments that may be combined with heat will all vary depending on the raw material.

non-heat treated tanzanite on the left and heat-treated tanzanite on the right

Non-heat treated tanzanite on the left and heat-treated tanzanite on the right


Our planet also naturally irradiates stones.  Irradiation can change the arrangement of the protons, neutrons, and electrons that make up the atoms of the stone.  This can alter the color of stones as well.  Man has figured out how to irradiate gemstones in order to improve color.  They can be treated to high energy radiation at a gamma ray facility that uses cobalt-60 so that there is no residual radioactivity.  Diamonds are sometimes irradiated to create beautiful fancy colored diamonds.  Colored diamonds can occur naturally, but it’s rare for them to be blue or green.  That’s why famous gems like the Hope Diamond or the Dresden Green are so amazing.   If you see a blue or green diamond, chances are man has irradiated it.  Blue topaz is another irradiated gem stone.  It’s the combination of irradiation and heat treatment that brings out that beautiful Swiss or London Blue in topaz.

The sun gave us inspiration for bleaching.  Stones often look prettier if they are whiter or less brownish.  Pearls and jadeite are both commonly bleached–and not by the sun. The process involves hydrogen peroxide or some type of acid.  Pearls, even if they are natural in color rather than dyed, are still often bleached to lighten and brighten the color nature gave them.

Unbleached jade on the left and bleached jade on the right

Unbleached jadeite on the left and bleached jadeite on the right


Most people in the jewelry industry accept these three treatments.  Since heating, irradiating, and bleaching could have all occurred naturally, it seems that man is helping out by making a natural process accessible to more gemstones.  And since all of these treatments are permanent, no one has to worry about their gemstone changing over time.  Finally, without these treatments, colored gemstones and pearls would be much more expensive and exclusive.

Our final post of this series will be about treatments that are not as commonly accepted.  These are treatments you, as the consumer, should definitely be aware of before you buy.  Treatments such as surface coating and fracture filling can enhance the look of the stone but may not be permanent.  Remember to ask questions if you want to know about treatments on a gemstone you’re planning to purchase.