It’s Getting’ Hot in Here!!! What’s The Deal With Heat Treated Gemstones?

If you’re not a gemstone expert, the concept of treating gems using heat may sound pretty random and confusing. A whole host of questions come to mind for the gemstone novice when it comes to heat treated gems. What does heat do to gemstones and why would people even think to expose gems to high heat? How are gemstones heated and how does this affect the value? Is a heated gemstone still considered natural? In the spirit of the summer months, it seems like an apropos time to discuss heat and answer all of the aforementioned questions. So turn up your air conditioner, grab a cool drink and get ready for a heated discussion on gemstone heat treatments!

The history of heating gems and stones to change their appearance dates back to the beginning of the gemstone industry. The earliest historical written account of gemstone treatment comes from the writings of Pliny the Elder, an ancient Roman philosopher, discussing treatments used to create counterfeit Emeralds and Carnelian gemstones. There are also early Egyptian and Arab writings that detail the process of using heat treatment for corundum minerals. While there is no historical record of the first person to discover heat treatment for gemstones, it seems that as long as there has been a gem trade there has been knowledge of how to harness the magic of heat to improve gemstones.

One way to think about heat treatment, which is considered a natural treatment, is as a continuation of the formation process that the gem would have undergone had it remained uncovered in the earth’s surface. Meaning, at the time it was mined the gem was not done cooking, so to speak, and just needed some more time in the oven. The heat treatment process involves heating the gem in a kiln or oven at temperatures ranging from 200 to 2000 degrees Celsius, often times in controlled environments that protect the stone from oxygen and airborne elements. The result of applying this sort of heat treatment can take an unattractively colored stone and transform it into something much more beautiful and valuable. In addition to affecting the color, heat treatment can cause impurities to reform themselves and dissolve inclusions within the gemstone.

Heat treatment can affect the color and character of different gemstones in different ways. For example, pale Amethyst gemstones, a purple variety of quartz, will turn yellow after heat treatment and can be sold as Citrine, the yellow variety of quartz. When Morganite gems are heated their color changes from orange to pink and heat applied to Aquamarine gems removes green undertones and deepens the blue color of the stone. One very cool example is the milky white colored gouda white sapphire which turns into a classic blue sapphire from heat treatment.http://www.africagems.com/aquamarine.html

The presence or absence of oxygen within the kiln can also affect the outcome of the treatment. For example, a purple sapphire heated with oxygen will result in a pink sapphire, as the presence of oxygen removes the blue color. When rubies are heated with oxygen the red color is more pure and it will remove any purple tones.

Gemstones that are often treated with heat include Amethyst, Citrine, Aquamarine, Ametrine, Tourmaline, Topaz, Sapphire, Ruby, Tanzanite and Zircon. And while heat treatment is not always discernible by a gemstone laboratory since it mimics the gem formation process, AfricaGems always discloses whether or not a gem has been treated.