Heat Treating

We own and operate our own heat treating furnaces and specialize in heat treating Gem Mountain Sapphires.

Heat Treating sapphires is a standard industry practice that improves the clarity and enhances the color of sapphires from Gem Mountain.  Most people prefer the darker color saturation and improved clarity and brilliance of a heat treated stone over the pale pastel color of the average rough sapphire.  We are one of only two locations in North America that offer heat treating services for retail customers like you.  We specialize in heat treating sapphires from Gem Mountain but can consider heat treating sapphires from other locations after examining the stone in person.

The cost of heat treating starts at $34 for up to five carats.  Charges are based upon weight at $6.50 per carat for up to 20 carats with price breaks for larger quantities.  Click on this link to open our heat treating and faceting price list.

We reserve the right to charge by the “piece” rather than the carat if your order consists entirely of small stones averaging less than one carat each in size.

We handle each order individually and promise you get your gemstones back. We offer a full replacement and refund guarantee but cannot predict the final color, quality or value of your sapphires prior to heat treating and faceting.

Most people don’t know that almost all gemstones are treated in one way or another to improve their “looks” before being sold as a gemstone in jewelry.  The list of treatments is extensive and includes everything from radiation, high temperature and/or high pressure heat treatment, waxing, oiling, epoxy and more.  In the case of sapphire high temperature heat treatment is a standard industry practice that frequently improves the color and clarity of the stone.  Heat treating creates a permanent and stable color change in the stone as long as the stone is not exposed to an extremely high heat source.  The extreme heat of a jewelers torch can cause a sapphire to crack and change color.

The heat treating we supply is considered 100% natural within the industry, because we do not add any artificial ingredients, fluxes or chemicals to influence the color of the stone. (Yes, there are methods whereby chemicals or a flux can be added to the heat treating crucible to induce color in the stone). In laymen terms, sapphires from Gem Mountain are only “half cooked” and are relatively high in iron resulting in the pale green color. Our high temperature heat process finishes the chemical reaction of the naturally occurring mineral impurities within the stone. The final results are totally up to “Mother Nature.” The vast majority of stones improve; however, some do not.

In general, heat treating will improve the natural color trend of the rough stone. If the sapphire has a yellow spot or hue, there are improved odds it will become a brighter yellow. A hazy stone with “silk” (the mineral rutile, which is high in titanium) will frequently become a spectacular blue. The clarity of pink stones can be improved, and sometimes an orange coloration will develop creating the very desirable “padparadscha” color. However, “Mother Nature” will frequently throw us a curve ball, and the heat treated stone can be a totally different color. Because the heat treating we undertake is natural, the final color of your sapphire will not be known until after the stone is heat treated. Like predicting the weather, we can offer predictions on what color the stone will become, but we cannot predict the final color with an absolute degree of certainty.

If your sapphire has good clarity and a color you like…DO NOT HEAT TREAT IT.  We always suggest faceting good natural color stones as a “Natural”.  Remember, we heat treat to change the color on purpose, so if you like the natural color of your stone, don’t heat treat it.  The only exception to this rule is if the stone is hazy.  Heat treating will improve the clarity, but you must be prepared to possibly have a totally different colored gemstone.

We undertake a two step heat treating process to maximize the value of the sapphires. The first step is the “Fancy Burn” where the stones are heated to over 1400 degrees Celsius in an oxygen rich environment. Almost all of the sapphires will turn yellow or orange to some degree. The color sort is a very time consuming and tedious process. Many of the sapphires will have a yellow spot on the “end”. We have to evaluate each stone individually to ascertain the depth of the color saturation. If we feel the stone has enough color saturation, we will pull it. Although almost all of the sapphires exhibit a fancy color, we only pull approximately 15% of the sapphires for faceting after the fancy burn.

After the Fancy Burn, we complete the “Blue Burn” at even higher temperatures in a slightly reducing environment. The Blue Burn finishes the chemical reaction of the naturally occurring iron and titanium within the stone. The more titanium the better the blue color. Approximately 45% of the stones will become a spectacular blue with the remainder being teal blue to green.

All gemstones are the ultra pure variety of a more common mineral. In the case of sapphires, the mineral is corundum. Corundum is composed of di-aluminum trioxide, Al2O3. It is the second hardest natural mineral on earth with a Mohs hardness of 9. That is why it is such a durable gemstone. Common corundum is used to build emery boards, high quality sandpaper, and grinding and cutoff wheels for metal working.

In its pure form, corundum is known as the sapphire gemstone and is perfectly colorless. White sapphires are commonly used as a diamond simulant to help reduce the cost of jewelry. When impurities occur in sapphire it creates color. The mineral iron creates yellow. In general, the sapphires from Gem Mountain are high in iron which is why most of them exhibit a yellow color after the Fancy Burn. Chromium creates pink and red. A Ruby is a sapphire with enough chromium to make the stone appear red. The presence of iron and titanium creates blue. The Blue Burn completes the chemical reaction between the naturally occurring iron and titanium in the stone to create the blue color.

We have two photo albums on our Facebook page that show before, during and after pictures of heat treating.  

The first is “Heat Treating” and the second is “Heat Treating Cut Stones”.  View The Galleries >


Mine Location

21 Sapphire Gulch Lane
at mile marker 38.4 of Montana Highway 38, Skalkaho Pass Road, between Hamilton and Philipsburg.

Year-Round Phone: (406) 859-GEMS (4367)

Mine Phone: (406) 859-MINE (6463)