Before & After, heat treating Montana sapphires

[SapphireNut1]

Here are four sapphires from the rock creek, Montana, deposit. I signed them out of our guild collection as four uncut stones, cut two of them, then sent all four off to be heat treated. This was an educational project for our guild members, I ended up doing a newsletter article on them, then the stones were sold by the guild during the fundraising action.

Of the two cut stones the far left definitely did not need heating. It didnt have much silk and was a nice yellow. The other was sleepy due to having more silk.

The uncut stones came back darker than the cut stones which may be coincidental or may be because the uncut stones had more volume and more silk to turn blue.

The cut stones came back a lighter blue, but required complete repolishing which took as long as cutting them.

While the heat treat facilities always have disclaimers about not guaranteeing a color change or the resulting color, I've had quite a few done and they tend to be a pretty consistent color range. The process is a first "burn" and inspection, a few will end up fancy colored (usually yellow) then they are heated a second time to take them all the way to blue.

Yellowish stones is the before photo. I took this with an old crappy lightbox so yes I had to adjust the color to represent the color of the stones accurately

 

[SapphireNut1]

Here are all four after cutting the other two stones. They are not in the same order, but you can recognize the color of the two that were cut before heating, they are the two stones on the right in the next photo. The two in the left were cut after heating and are darker blue

 

[Musia]

Thank you for posting, your experiment was very interesting!

 

[EvanFancy]

Nice, thank you for this post

 

[LilAlex]

Very helpful -- thank you!

 

[Essiedub]

Here are all four after cutting the other two stones. They are not in the same order, but you can recognize the color of the two that were cut before heating, they are the two stones on the right in the next photo. The two in the left were cut after heating and are darker blue

Wow. So interesting! Do you think if you’d cut those 2 uncut ones prior to heating, then heated, that the end color would still be the same? I suspect the answer is yes. Are stones typically heated prior to cutting? Through experience, you’d be able to guess the final outcome color? Thanks for the informative post!

 

[SapphireNut1]

Wow. So interesting! Do you think if you’d cut those 2 uncut ones prior to heating, then heated, that the end color would still be the same? I suspect the answer is yes. Are stones typically heated prior to cutting? Through experience, you’d be able to guess the final outcome color? Thanks for the informative post!

What turns the stones blue is the burning off of rutile silk. I *think* those two stones would have been lighter blue if cut first, then heated, but I don't know. Just a guess because there would be more rutile silk (by volume) in an uncut stone. I'm sure the guy that does the heat treating would have a better answer.

Most sapphires are heated before cutting, it's just less total work. The only times I've known cutters to heat after treating is if the stones were sleepy and didn't sell. Tourmaline and tanzanite are often heated after cutting, the temps used on them don't get high enough to hurt the polish. With tanzanite, the stone really needs to be flawless to survive heating. I have a 71 carat tanz rough, at the minimum I'll preform it before heating, if I ever cut it. With the changes in Tanzania its not a piece of rough I can replace

 

[Essiedub]

What turns the stones blue is the burning off of rutile silk. I *think* those two stones would have been lighter blue if cut first, then heated, but I don't know. Just a guess because there would be more rutile silk (by volume) in an uncut stone. I'm sure the guy that does the heat treating would have a better answer.

Most sapphires are heated before cutting, it's just less total work. The only times I've known cutters to heat after treating is if the stones were sleepy and didn't sell. Tourmaline and tanzanite are often heated after cutting, the temps used on them don't get high enough to hurt the polish. With tanzanite, the stone really needs to be flawless to survive heating. I have a 71 carat tanz rough, at the minimum I'll preform it before heating, if I ever cut it. With the changes in Tanzania its not a piece of rough I can replace

The whole topic of heating and cutting is so fascinating. Now that I’ve spent more time on this forum, I think I should consider getting some stones recut and now it seems I could theoretically even get some heated to reduce sleepiness. Do you know if these services are available to a regular consumer and how much that would cost..ballpark? Thanks for your great post.

 

[lknvrb4]

So I have a question on about Montana sapphires. I just bought one and I am told that most Montana sapphires have gray in them. My issue with this one is that it shifts to almost a dark gray/black cloud when I move it around in different lighting. It's like one end turns dark while the other isn't. Is this how they all behave?

 

[SapphireNut1]

The whole topic of heating and cutting is so fascinating. Now that I’ve spent more time on this forum, I think I should consider getting some stones recut and now it seems I could theoretically even get some heated to reduce sleepiness. Do you know if these services are available to a regular consumer and how much that would cost..ballpark? Thanks .

It's not expensive, but you'd have to have your stone polished again if it was heated after it was cut. I *think* it was around $50 total for the four stones I posted. It isn't much, it depends on weight. However getting a stone that was heated after cutting repolished would (or should) cost at least as much as the original cutting charge. It's a headache to polish it without screwing up all the meet points.

 

[SapphireNut1]

So I have a question on about Montana sapphires. I just bought one and I am told that most Montana sapphires have gray in them. My issue with this one is that it shifts to almost a dark gray/black cloud when I move it around in different lighting. It's like one end turns dark while the other isn't. Is this how they all behave?

That's pretty wild that it only color changes on one end. If it's always the same half of the stone then it's a feature of that stone. If you can get the color change to rock back and forth from end to end then its how the stone was cut, combined with the stones color shift.

Most heated montanas dont do a big color change in different types of light but the blue will have a steely color to it. You can get some pretty dramatic color changes out of unheated montanas.

 

[lknvrb4]

That's pretty wild that it only color changes on one end. If it's always the same half of the stone then it's a feature of that stone. If you can get the color change to rock back and forth from end to end then its how the stone was cut, combined with the stones color shift.

Most heated montanas dont do a big color change in different types of light but the blue will have a steely color to it. You can get some pretty dramatic color changes out of unheated montanas.

Thank you. It shifts from end to end for sure. I'm great with a steely blue, its the dark black cloud that it looks like that bothers me. It is so hard looking for a Montana.

 

[PieAreSquared]

Thank you. It shifts from end to end for sure. I'm great with a steely blue, its the dark black cloud that it looks like that bothers me. It is so hard looking for a Montana.

What you are seeing is what PSers call "half and half shadowing" (sometimes mistakenly called 'half and half extinction') and is a feature on most elongated stones, rectangles, ovals, etc. It comes from light being reflected back at different rates.

It's not "pretty wild", it is very typical, and has been discussed on PS at length. It can be minimized by setting the stone East-West, but if it really bothers you, you should probably stick to a round or square shaped stone.

And yes, Montana sapphires are shifters, heated or not, I think Sapphire Nut thinks presumes to know more than he actually does, regardless of what he calls himself.
No true professional would assert that shadowing could be "fixed" by "changing the pavilion facets" without even seeing the profile or bottom of the stone.

 

[lovedogs]

What you are seeing is what PSers call "half and half shadowing" (sometimes mistakenly called 'half and half extinction') and is a feature on most elongated stones, rectangles, ovals, etc. It comes from light being reflected back at different rates.

It's not "pretty wild", it is very typical, and has been discussed on PS at length. It can be minimized by setting the stone East-West, but if it really bothers you, you should probably stick to a round or square shaped stone.

And yes, Montana sapphires are shifters, heated or not, I think Sapphire Nut thinks presumes to know more than he actually does, regardless of what he calls himself.
No true professional would assert that shadowing could be "fixed" by "changing the pavilion facets" without even seeing the profile or bottom of the stone.

This this this. Also @SapphireNut1 , please read forum rules about things you can vs cannot say as a trade member.

 

[SapphireNut1]

This this this. Also @SapphireNut1 , please read forum rules about things you can vs cannot say as a trade member.

I'm definitely learning what I can, and can't say the hard way. I figured if it was a question to me on my post I could address it. It's fine if I can't.

 

[Rfisher]

Ya its going to be a keel pavilion with chevron type facets. It's pretty simple to change those without a huge loss of weight. Going to wider facets instead of sharply angled chevrons will usually take care of the extinction, or just changing it to a traditional step pavilion.

If you can petition for the mods to allow you to post a stone you’ve done this on, it would be pretty educational to see the before and after photos!

 

[SapphireNut1]

If you can petition for the mods to allow you to post a stone you’ve done this on, it would be pretty educational to see the before and after photos!

most folks using design software are going to avoid it in the first place. The model will show the extinction at different tilt angles and you change angles or use a different design. You try to avoid black ends and bowties in ovals, black noses on pears during the design stage.

I think it would be legal to do a before and after render (animation), virtually cutting the stone. Probably best for another post.

 

[Rfisher]

I’m all for technology advancement.
But think seeing actual stone recut before and after getting rid of what and how you describe would be much more fascinating than a rendering.
Thanks tho.

 

[2Neezers]

I sent a couple of elongated stones that had the half on/half off effect to Jerry at Gemart for a pavilion recut. They both had keel culets and he recut them to a pointed to culet. It helped lessen the shadowing effect a lot! It was so long ago that I couldn’t find the before pictures, but I’ll keep looking and will post them if I end up finding them.

 

[PieAreSquared]

I think it would be legal to do a before and after render (animation), virtually cutting the stone. Probably best for another post.

If you are suggesting you do a "virtual recut" of another vendor's stone, NO, I don't think that would be "legal" here.

I like @Rfisher s idea, how about you show us your own before and afters?

I would be very interested to see how your proposed solution would avoid shadows on a rectangle while also, most importantly, maintaining the color of a natural sapphire.

 

[SapphireNut1]

If you are suggesting you do a "virtual recut" of another vendor's stone, NO, I don't think that would be "legal" here.

I like @Rfisher s idea, how about you show us your own before and afters?

I would be very interested to see how your proposed solution would avoid shadows on a rectangle while also, most importantly, maintaining the color of a natural sapphire.

Not at all what I'm suggesting. It's easy enough to draw up a design that produces an extinction area (or you use a design that's in the public domain) the rendering will show the dark areas as you tilt it. You then alter the design in the software and do another rendering to show the change in the extinction pattern.

In real life, you'd just dop up the stone and change it, as you get pretty good at understanding what will work and what won't. It's a similar process to closing a window. There are a lot of people who are very good at doing this on the fly because stones that aren't correctly cut (speaking generally, not at any stone in this thread) can often be bought at a bargain and fixed with a very small weight loss. You dont want to change anything more than you have to, as both time and carat weight are money.

 

[MollyMalone]

In light of some of SapphireNut1's comments in the past couple of weeks & his latest responses in this thread, I'm thinking this would be an appropriate time and place for this piece by the late Jeff Graham that the International Gem Society published some years ago:

Master Faceter - International Gem Society

Jeff R Graham shares his opinions and thoughts on various topics in Just Ask Jeff. See what a "master faceter" is in Just Ask Jeff: What is a Master?

www.gemsociety.org

For those who don't recognize the name, Mr. Graham was a well known lapidary whose faceting designs and instructional guides gained him wide recognition before his premature death at the age of 49. Condolences and comments from, e.g., Peter Torraca, Lloyd Forrester, and Richard Wise here:

GemologyOnline.com • View topic - Jeff Graham RIP

 

[Ella]

**edited by moderator** I don't think I'm allowed to post names (it may even be against the rules for me to comment on your stone since I'm technically in the trade).

Correct, this is not allowed as we’ve been messaging you about. Please read the policies.

Technically you aren’t allowed to post photos or show off items you have cut/sold/in inventory either. We will allow this thread to remain as it is clearly educational, but in the future you must ask for permission before posting these kinds of things.