Setting with heat

[FrekeChild]

So what stones can be set with heat, and which cannot? I've been searching for the answer, but I don't think I am searching for the right terms, because I haven't found any answers!

 

[PinkTower]

Peter T. advised me not to allow heat near my danburite.

 

[LD]

Freke - I'm really not sure about this but I think that heat is used to set gemstones (i.e. soldering, bending prongs over etc etc). With stones that don't like heat (Tanzanite springs to mind), the setter has to be very careful. I'm not sure if they can use an alternative to heat but if not then I'm guessing it comes down to the skill of the setter.

I also presume that the care that needs to be taken correlates to the MOHS hardness of each gem.

Hope that helps but it's a big guess!

 

[Lady_Disdain]

Heat is not necessary for setting stones - all soldering and annealing is done before that step. Even heavy bezels are closed without heat.

Heat, however, is used in repair work: resizing rings, reshanking and retipping prongs. So, in these cases, always talk to the person doing the repair (salespeople often have no idea how the work is going to be done). Sometimes, the stone doesn't need to be unset (using heat shields or sinks, laser welding), often, it should. Very few stones can withstand heat (basically diamonds and sapphires, although sapphires should never come in contact with the pickle used to clean up after heat, as it etches the stone).

 

[zeolite]

Heat is not necessary for setting stones - all soldering and annealing is done before that step. Even heavy bezels are closed without heat.

Heat, however, is used in repair work: resizing rings, reshanking and retipping prongs. So, in these cases, always talk to the person doing the repair (salespeople often have no idea how the work is going to be done). Sometimes, the stone doesn't need to be unset (using heat shields or sinks, laser welding), often, it should. Very few stones can withstand heat (basically diamonds and sapphires, although sapphires should never come in contact with the pickle used to clean up after heat, as it etches the stone).

You must be thinking of peridot, which can be etched by acid.

Sapphire is widely used in semiconductor manufacturing, because it is almost totally impervious to acid.

http://www.generalruby.com/sapphire.html
Chemical Resistance:
Inert to virtually all reagents at room temperatures and many at high temperatures. Essentially inert to all acids including HF, and resistant to alkalis but becoming soluble at higher temperatures.

http://www.namiki.net/product/ybo/sapphire/index.html

3. Chemical resistance and heat resistance
- resist almost all kinds of acid and alkaline, heat up to 2000 ºC.

http://www.chonghong.com/Products-ch/sapphire-ruby.htm

Chemical resistance - high inert and resistance of sapphire makes it's character hard to be changed in most process environments including hydrofluoric acid and the fluorine plasma applications generally in semiconductor wafer processing. Quartz and polycrystalline alumina and other ceramics are damaged and corroded in similar environments.sapphire windows and optics remain free of damaged.

 

[Lady_Disdain]

Zeolite - boron based pickle does etch sapphire, as several jewellers have found out. Around here, boron pickle seems to be quite popular (more so than sparex and I even know a few who still use sulfuric acid - ouch!).

For example, from the archives of Ganoksin:

"Don't coat sapphire or ruby with boric acid to protect the stone during soldering. Although this is common practice with diamonds, heated boric acid will etch the surface of corundum." (ok, this is during repair, but the logic is the pretty much the same)
http://www.ganoksin.com/borisat/nenam/jewelry-design-and-repair.htm

There was also an interesting discussion on the list:
http://www.ganoksin.com/orchid/archive/200104/msg00265.htm

I believe the GemDoctor also mentions this somewhere on the web, but I might be wrong.

I have a few other sources, but I am unable to get to them at the moment (oh, my dear books!)

ETA - I was thinking a bit more about the boron connection. Even though no one mentions this, perhaps this affects glass healed sapphires? The boron may be a tip off...

 

[FrekeChild]

Oh boy, all of this is going over my head. So is spinel heat resistant? (Believe it or not, I do own other stones...not many though!)

 

[iLander]

I don't know about spinel, I just wanted to answer the OP (since that is the full extent of my knowledge )

Setting a stone is often times just bending the little prongs with pliers. I've done it with specialized setting pliers, and it's not rocket surgery. Usually no heat required.

I usually only set inexpensive stones for family and friends, but I did manage to set a fire opal, which is a pretty soft stone. I didn't know at the time what kind of chance I was taking (apparently it's pretty brittle and soft), but it went fine. I don't know how some of these professional setters manage to mangle stones . . . but unless they're sizing the thing, they shouldn't be heating it . . .