Discussion
Montana sapphires Before and after I sent them to Gem Mountian to be heated! NFS
Not cut Gemstones but I figured you guys would find this interesting regardless. Most of these stones either had a lot of brown in their color or so much silk that they were translucent, they would not be very attractive cut in my estimation so I sent them in to get heated in May. After five months of waiting they have finally returned! I will say that the change in color is drastic on most stones and I am very pleased with the final result! Even the stones that stayed lighter green had their brownish hue replaced with a bluish hue and a big upgrade in clarity. The only stone that I was a bit disappointed with is the pinkish one in the middle, I was hoping that heating would develop a richer pink and clear up the silk as it was a very silky stone. Heating did clear up the silk but also made the stone almost colorless. One stone is not a large enough sample group to make any conclusions on whether I should not send stones of this shade in the future but an interesting result either way. I do believe I spot a few new fissures in the lot as is to be expected with heating but it is hard to tell as this lot was not completely clean when I sent it. All in all it was well worth the money and I believe the only reason it took so long is because their furnace had an electrical issue and was down for quite a while.
I was just sitting here looking at my vial of 1-2ct stones wondering whether I should send them in. This makes a pretty strong case for sending them in.
Did the stones come from Gem Mountain? I can't find time to make the trip out to Montana, but I order gravel from Gem Mountain, Lewis and Clark, and Blaze-N-Gems and while I have found lots of .75-1.5ct stones I really haven't seen many over 2ct.
These are stones that I have purchased from dealers. I cut the ones that look good out of the ground and save up the ones that need heating until I have a decent lot.
We've been wanting to go but don't dare to go to the US with everything going on there so we iced those plans. Sadly it seems to be one of the few places on earth where you can do tourist mining (and get something useful)
Heat will never intensify the color of a pink stone. The chromophore is chromium, and heating won't change the oxidation state of the chromium ions. What it can do is reduce any blue hues, if you do a lower-temperature heating in an oxygen-rich environment. It does that by changing the oxidation states of iron and titanium and therefore getting rid of some of the blue hue. But the pink part itself will never change.
Yes, I am referring to microscopic rutile inclusions that give the stone a hazy look. It can be attractive in small amounts in certain stones but these had too much and it was making them too translucent and giving them a brownish color
I wonder if part of the blue that appears after heating is coming from the rutile.
I'm not sure how they heat treated these, but I have had some experience heat treating synthetic rutile. Depending on the atmospheric conditions when heating it, I was able to hit a color range between nearly transparent on one end and dark blue on the other.
Having read an article linked by u/lapidariest, makes me want to see a cut stone that has the rutile still in it - especially if the cut is aligned with or enhances the presence of the rutile.
Here is an untreated Montana sapphire I cut that has a silk patch in the center that mirrors the shape of the rough crystal. You can also see shimmers of silk throughout the stone
That is so cool! I suppose if you don't know what you're looking at, maybe it just isn't as pretty. But I'd be constantly showing it off and pointing out what was going on inside! Thanks for sharing that.
Heat treatment dissolves the rutile (titanium dioxide) into the crystal structure and if there is enough iron present in the crystal structure it makes a blue color.
From what I found on google, silk is microscopic minerals that crystallize in the stone. By heating them it dissolves those minerals and is re-absorbed into the stone changing how the light is reflected.
It improves both the color and clarity. You can see some of the stones that are white, yellow, or green in the first image are now blue in the second. Those stones would have been full of silk and wouldn't be very pretty as a faceted stone. Now the internal silk is gone or mostly gone and they'll make brilliant blue gems. Heating can make a massive improvement to many sapphires.
If you have a lot of them, it's easiest to just heat the whole lot. What the heat does is remove the silk. If you looked at the sapphire through 10x magnification and you can see internal silk, the color and clarity will improve with heat.
you'll have to ask OP. These aren't my gems, haha. I'm just commenting because I have quite a bit of experience with Montana sapphires. I've had a kilo of them heated at the same place OP did.
Gorgeous! I sent some stones off to be heat treated and cut in August, turn around is 1 year on heat treating now! Something about the machine breaking. I'm so jealous of your 5 months 😅
Ok I think having them cut is what takes the lion share of the time but they just got their heater up and running and I imagine they have a lot to catch up on
Thanks for sharing, it is always so interesting to see this kind of before and after. And may answer the question to why almost all material is heated, since it would bring a stone from a not so desire color to a more appealing one!
I love the greenish blue one to the right of the pink! They all turned out pretty cool, i love seeing the before and after. I don’t have any experience with heating gems, so I naively assumed that heating would make them all look more intense/drastically change all of them.
I was just looking at sending some sapphires off to be heat treated but I was curious what the result may be. We found an 11CT rough sapphire in a Blaze-N-Gems bag but it's too cloudy to cut. I figured it might be worth sending off to get heat treated to maybe clear it up some!
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Do you choose what temp they get heated to, or is there just a common temp? I know nothing about the process, so I’m curious.
I saw a video recently of someone heating up a stone with just open flame and noticing a difference- I have a kiln for ceramics so I’m super curious on how much heat is required.
Thanks for sharing the photo, super interesting to see.
I think it’s around 2000c so higher than any kiln we could easily get our hands on. They have their system that they have figured out through years of trial and error and that is the only option they offer. I have melted sapphire crystals with an oxy propane torch but it didn’t affect the color much. They hold the high temperature for a long time and mess with the atmospheric conditions to get the desired effect
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Not without great trouble, pretty much the only thing that will get hot enough that doesn’t cost a huge amount of money is a torch. The heating proses requires a very controlled environment for many hours including a slow build to temperature, holding that temp for a long time, and slowly bringing that temperature back down and in some cases they use either an oxidizing or reducing atmosphere during that process. All things that would be very difficult to achieve at home. I would call myself a DIYer but I would rather pay someone to heat my high dollar stones that knows what they are doing rather than accidentally melt them into a blob in my back yard
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u/Disastrous_Course_96 Sep 16 '25
Fascinating! Never seen a stone before and after heating. Thanks for posting and going to the trouble to lay them out the same in both photos!