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How much heat can i apply to a sapphire mounted on a piece

my sapphire crack after i apply heat to the piece i was using thermo- blanquet to cover the saphire but even with the protection it cracked can someone has an answer or helpme with this and how to avoid this problem in the future

Sapphires are very heat resistant, maybe the gemstone that takes the most heat.
Two possibilities stand out in my eyes:
If they have invisible damages, crack lines and such it will be weaker and may crack under stress.
Or maybe it’s not a true Sapphire?

Regards PoA

thanks , could be i test it and its a sapphire but maybe it had the not visible lines like you said or maybe i quench the piece too fast and the stone endup cracking

While Sapphires can take high heat, and supposedly you can even retip a prong without removing the stone ( which I have done many times), I once had a really nice Sapphire suddenly split into two pieces as I was soldering the prong.
I took it to a friend who had a Gemology ID and appraisal business, and he determined that the Sapphire had formed around a second, smaller Sapphire crystal.
What happened to me appeared to have been that the smaller crystal expanded at a different rate than the larger crystal around it, when heated to soldering temperature, and acted almost like a splitting wedge in firewood!

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wow thats an interesting experience tou had with a sapphire , i have a friend also that had a similar experience with a sapphire that had tyni gas bubble inside and when the sapphire got hotter by the torch near by the gas spanded and busted a hole on the table of the stone . so i think that what happens to mine could be a thermoshock , maybe i quench the piece too quick i did not give the piece enough time to cool down

Any stone you put in the fire should be allowed to cool, away from any drafts, until it is cool to the touch.

yea i lnow the hard way now . thanks

Yes, quenching is not always a good idea.
Quenching a hot item can shock any stones and it can harden White Gold.
Quenching can even destroy a diamond.

well i was not actually too hot when i quench it but i guess it has to be cool temperature , and the white gold that actually gets hard when you quench is the the one made with the cheap nikel alloy but if you use palladium you wont have a problem

like i said that was a costly mistake for me next time if i cant unmount the stone i will be extra carefull to make sure i dont put the piece in the pikle solution untill is cool temperature . thanks for the advice

My rule of thumb is to never take heat to any stone I cannot afford to replace.
Now that said… here are a few important rules and info on Sapphires.
Never ever get flux or boric acid on any form of corundum. Be it any color saph. or a ruby. When heated the flux will bond with the stone and leave an orange peel texture. So you have to buy a replacement.
Almost all forms of corundum are heat treated. that’s normal. Though over heating one can remove the color. So you have to buy a replacement.
Almost all of the corundum on the market today are fracture filled and heat will make them break, and a sonic cleaner and or steaming them can remove the filler leaving the stone looking like a fired glass marble. Again the jeweler looses.
I have witnessed all of the above tragedies occur in trade shops where the jeweler was in a hurry or got cocky. About 40 years ago I once warned a boss of mine to not try to patch a bezel on a custom cut 12 kt golden sapphire while it was still in the mounting. He told me to shut up and go back to my bench. The stone lost all of it’s color. It turned clear white. Just like his face did when it happened. He then had to go out and buy a 14 kt golden sapphire and have it custom cut to fit the mounting. Needless to say I got stink eye from the boss who already thought that he knew everything and that “girls are stupid”, and of course none of us in the shop received a Xmas bonus that year.


yea thanks for the reply mine was not fracture filled but not it is fractured for sure lol , is the purple sapphire on top of the piece .

after i cracked internally by probably putting the piece in the pickle pot to fast , never again i will do that ,i will wait untill is completly room temperature . thanks for the advice

I don’t work with diamonds, so I can’t say that you can’t solder next to them, but, as a gem cutter, because of all the strange things that happen once in a while with ANY colored stone, I would never solder near one. There is always that rogue stone that has some internal inclusion or stress in the crystal that will fracture with the heat. There are lots of cutters who will put rough in the oven to cure epoxy before cutting or in the freezer to release wax off a dop, but I never do any of that and limit any heat on the stone to that required to get dopping wax soft…not molten, but soft, so maybe 180*F, tops. I make an impression in the wax with the stone and then glue it (CA glue) into the impression. I just feel more comfortable that way. Some stones won’t take any heat at all, and those you have to epoxy or use white glue on…rather safe than sorry…

Hello there thanks fir the advice , i would love to learn how to cut gemstone the proper way , i have the machine i just have to get start practicing , what machine you use a mast machine or a handpiece machine

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I use a custom mast type machine with an angle gauge to 0.01*…but people who use the handpiece machines love them…they make inspection a little easier. There are plenty of videos and instructions on line on faceting, which I learned from books back in the 90’s. It isn’t that difficult, there’s just a learning curve to it and you get better the more you practice. That said, there are workshops where you can go to learn, particularly the Wm.Holland School in the East and John Bailey’s school out on the West Coast. There are some others…

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cool thanks for the reply i have both the mast and the handpiece i want to learn with both

I would pick one and learn that first, as the adjustments are done a little differently with each. After the other processes are dealt with (cutting to meet points, setting angles, polishing, etc.) then you can learn the other machine. Most people prefer one or the other, altho’ I have known people who used both.

yea thats good advice i will do that i will star with the mast machine first

quenched it? no no no quenching let the piece cool down by itself

thanks for the advice