Post subject: anyone tried heating saphire as a diy project
Posted: Sat Sep 15, 2018 10:48 pm
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Joined: Tue Jul 02, 2013 9:00 am Posts: 1322 Location: Wylie Texas but in Alaska for a while
I was at Gem Mountain and we have several hundred carrots of stones. I found an article about heat treating that mentioned that that it can be done using oxidizing and reducing frames.
I have some insulating ceramic material that I can make a small furnace from and try to treat some of the fractured stones (I have several hundred carrots of them)
has anyone else tried this?
Any recommendations?
Does anyone have recommendations on how best to check the temp?
Post subject: Re: anyone tried heating saphire as a diy project
Posted: Sat Sep 15, 2018 11:06 pm
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Joined: Thu May 12, 2016 2:18 am Posts: 1542
wilsonintexas wrote:
I was at Gem Mountain and we have several hundred carrots of stones. I found an article about heat treating that mentioned that that it can be done using oxidizing and reducing frames.
I have some insulating ceramic material that I can make a small furnace from and try to treat some of the fractured stones (I have several hundred carrots of them)
has anyone else tried this?
Any recommendations?
Does anyone have recommendations on how best to check the temp?
Heating carrots is easy. My Wife just boils them on the stove. Add a little butter and they are delicious. Now, cooking carats of Sapphires is more complicated.
I was involved in Montana Sapphire back when American Gem had the mines. We heated hundreds of thousands of carats. Dr John Emmett did a very complete study of heat treating Sapphire as part of the project. He developed very advanced temperature and environment controlled electric ovens. I think these ovens are still regarded as the state of the art in the industry. Most of the heaters in Montana are using his ovens. I spoke to him early this year. I believe he is no longer heating Sapphire. I think he sold his last oven to Columbia Gem House, and trained them to heat.
The heating of Montana Sapphire is an iterative heat process. You do a series of burns in different oxidizing/reducing environments, at different temperatures, and for different times. After each burn, you take out the pieces that responded well to that cycle, and send the rest on to new burns. Normally starting with trying to achieve the best blue colors, and then moving on to the fancy colors.
I'm not sure how close you can come to maximizing your rough in a home made oven. The less sophisticated methods work well with the non basaltic sapphire found in the traditional Oriental deposits. That is why they are successful with the primitive ovens they use over there. More technical methods are required to improve color in Montana stones.
I think you will do better to pick some good candidates and send them in to be heated.
Post subject: Re: anyone tried heating saphire as a diy project
Posted: Sun Sep 16, 2018 11:46 am
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Joined: Thu May 12, 2016 2:18 am Posts: 1542
I am not sure Columbia is treating other peoples stones. The people at Gem Mountain will for a reasonable charge, and they get good results. Here is a link with a picture of one of Dr Emmetts ovens. The charge $6 a carat. There is a company in Sri Lanka that does it for about $2.50 a carat, but I don't know about their results.
Post subject: Re: anyone tried heating saphire as a diy project
Posted: Tue Sep 29, 2020 9:20 am
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Joined: Tue Jul 02, 2013 9:00 am Posts: 1322 Location: Wylie Texas but in Alaska for a while
do they heat treat before or after cutting? From an article and the samples of stones I have, some have a yellow center, I would think that you would want to heat treat before cutting, so you could orient the stone for best color,
I have had other projects going on, but recently got a n old small electric oven that I am thinking of adapting for the higher temps and environments needed for sapphire, I am confident that I can get the environment for the initial color burn at 1400c and pure oxygen done. The next burn envirnment will be a little more challenging.
Post subject: Re: anyone tried heating saphire as a diy project
Posted: Tue Sep 29, 2020 1:34 pm
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Joined: Tue Apr 05, 2016 7:58 pm Posts: 1424 Location: San Marcos, CA
Yes tried several times with a modified 2000 degree standard jewelry furnace, simply put got more heat... SDG&E loved it. Steve knows who my experiment partner was, we tried to cook the silk as supposedly less heat is needed but even then more heat required. But we had that furnace just a flaming away.
Post subject: Re: anyone tried heating saphire as a diy project
Posted: Tue Sep 29, 2020 7:23 pm
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Joined: Thu May 12, 2016 2:18 am Posts: 1542
It takes a very expensive electric oven with controlled environment to heat sapphire properly.
However, you can build a pretty good one cheaply if you want to do it Thai/Sri Lanka style.
The issue is that stones from different localities need to be heated differently. Additionally, stones of different types from the same location need to be handled differently. The heaters up in Philipsburg Montana have ovens and protocols developed with extensive scientific research by Dr John Emmett. Over time they have further refined the processes.
Consider that one properly heated stone that comes out with a very fine color could likely pay for the treatment of your entire lot. Your experimental heating would likely not get this result.
Sapphire is a non trivial stone with high value potential. Processing it should be as optimized as you can make it. Right now I have 1/2 kilo of very fine, very large blue sapphire rough from Ethiopia sitting in my safe. The Sri Lanka dealers are buying this type of material at very high prices in Ethiopia. I am waiting to heat them until I find the right heater with tons of experience with this material. I do not want to experiment with stones potentially worth tens of thousands each.
I think the melting of silk so that the titanium content of the rutile can take it's place in the sapphire lattice requires around 1900 degrees C.
I suggest you read Read Hughes Sapphire Ruby book for a good explanation of the chemistry of heating sapphire. Available from Lotus Gemmology in Thailand. This book belong in every Gemologists library.
I am looking at a Molybdenum Disilicide (MoSi2) Heating Elements
I am doing only a few at at time, so I do not need a very big oven at all.
It is something I have been thinking about for a while, and it will be a while before i get to it. I had a type R thermocouple givenj to me, if i can remember where I put it for safe keeping.
Post subject: Re: anyone tried heating saphire as a diy project
Posted: Fri Oct 02, 2020 9:39 am
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Joined: Thu Jun 14, 2012 7:58 pm Posts: 75
I heated a small amount of Montanas in loose investment in a small jewelry kiln (max heat 2000F) at about 1800 for an hour or so; slow ramp up and down. (By the way, loose investment EXPANDS when heated, so don't fill up your flask or crucible) I found that the blues didn't noticeably improve, but the green/grays did. Interestingly, it seemed to turn quite a few of them a yellowish and yellowish/orange color. May have been just an idiosyncrasy of the chemical makeup of the stones I had. They were Rock Creek sapphires.
The problem with some of the overseas heaters is that you don't know what they have used the kilns for before they heat your stone. So folks have had stones come back that are showing treatment with beryllium, probably unintentional and resulting from the kiln being contaminated. I'd stick with the heaters here in the States; they use heat only.
I plan to mess around with some of them again, next time in graphite or charcoal in an enclosed tin to create the reduction atmosphere. Let us know what your results are.
I use the Sapphire Gallery in Phillipsburg, MT for all my Montana Sapphire heat treating needs. Dale Siegford is the "cook" there, and he can advise on the best process for your rough. Be forewarned that any inclusions other than rutile will cause discoid fractures. Pre-existing fractures will expand. In the past blanket heat treatment of all Gem Mountain/Rock Creek rough was the norm, but the new Potentate operation up there is sorting pre-burn, and finding a small (but very valuable) percentage of rough which is marketable without heat.
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