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 Post subject: Heating Moissanite
PostPosted: Tue Jul 16, 2019 9:23 am 
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Heating moissanite to get back origin color after cutting

I am new in this so I have not work experience and I am looking for the best answer or your ideas about heating moissanite

Have anyone on this forum , heated moissanite before?
I am thinking of investing for proper lap and compound to cut rough moissanite and I will but a couple small pieces of rough

But I was told by expert that they change color after cutting to dark
So I thought the stone needed to heat to get back actual or origin color as it is industry acceptable process . I did search China market to understand or get an idea how to heat them to get back the original color but no one responded me with the solution so

If anyone in here have work experience with moissanite please let me know

And if I find the answer with the china manufacturer I will post it here for those who are interested to learn a bout it

Kindly appreciated


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 Post subject: Re: Heating Moissanite
PostPosted: Sat Jan 16, 2021 6:40 am 
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Looking to resurrect this thread.

I've cut a 2.5 ct square cut moissanite following a faceting diagram I optimized for the high RI using Gem Ray. The material originated from an optical SiC wafer and was clear/white in color. After cutting, taking care to minimize heating to the greatest extent possible, I now have a champagne colored stone, as expected.

Unable to find any real information, save for bits and pieces from published patents and forum speculation, I attempted heat treating at 850C overnight in an Argon atmosphere. This resulted in deposits damaging the surface polish, meaning I had to go back and refinish the final polish of the stone.

All attempts at contacting commercial moissanite producers (Fire & Brilliance, Colvard, Lang Antiques, My Moissanite) asking to pay for annealing services have failed.

Judging from the responses in the "Moissanite with no doubling?" thread (viewtopic.php?f=24&t=22126), I believe that there are members in our community that are able to help.

Does anyone have any information on how to anneal moissanite with whitening as a goal? I have significant laboratory equipment with which to use, including access to an atmosphere controlled furnace. Alternatively, I am open to for hire services.

Thanks in advance for the advice.


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 Post subject: Re: Heating Moissanite
PostPosted: Sun Jan 15, 2023 10:26 am 
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The temperature above which Moissanite changes color would be around 80 degrees Celsius. I know a cutter who never exceeds this temperature. Therefore, his Moissanites never change color. He did however give me some information about the treatment that allows Moissanites to return to their original color after they have been cut at degrees above 80 degrees Celsius. This procedure has not been verified. It should be applied with caution.

Place Moissanite in a heat resistant container (steel, clay, etc). Wrap them in thick layers of ash and sand to slow down the heating and cooling rates. This avoids thermal shock which can cause damage. The first layer must be of ash to avoid any abrasion of the Moissanites. The stones are then placed in the furnace.

The temperature is raised to 600 degrees Celsius, at a rate of 50 Celsius per hour for the first 150 degrees, and 20 Celsius per hour for the next 450 degrees. We keep this temperature level (600 Celsius) for 6 hours. We then cool down at a rate of 20 Celsius per hour.

This procedure is quite long. The heating and cooling steps can surely be faster. But this avoids the possibility of thermal shocks. The duration can vary depending on the size of the stones (small ones are more resistant to heat) and the number of stones heated simultaneously.

I have never cut or heated Moissanites. However, I would like to do so. Please feel free to correct or complete the information I have just given. They may be wrong or need to be presented with more precision.


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 Post subject: Re: Heating Moissanite
PostPosted: Mon Jan 16, 2023 10:00 pm 
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Hey there - the other important thing for you to remember is that it depends on the polytype of moissanite. 3C moissanite is always yellowish and won't improve by heating. 4H is generally very stable and won't change colour while cutting, while 6H is a bit less stable and will yellow if you get it too hot during polish.


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 Post subject: Re: Heating Moissanite
PostPosted: Tue Jan 17, 2023 11:14 pm 
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My supplier just told me that the polytype of the rough he sold me was 4H. So the color shouldn’t change while cutting or during polishing. If it does, I will try to heat treat the gem using the procedure I just talked about. I will keep you informed.

Thanks a lot for your help.


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 Post subject: Re: Heating Moissanite
PostPosted: Sat Jan 28, 2023 12:38 am 
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[video] https://youtu.be/c-G14m3MLRg[/video]I

finally cut my first Moissanite. It is an antique cushion square measuring 10.0 mm and weighing 4.50 cts. Curiously, I never felt any heat except when I sawed the rough piece. The color of the cut stone is identical to that of the rough (the stone did not turn yellow or brown during cutting). I must say that I had taken several precautions, despite the fact that this is a 4H prototype which is supposed to not yellow. Thank you for your information, Arya. It really helped me to undertake this cut in a much more relaxed way.


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