I am doing some copper enamel artwork and I have an idea to include small gemstones in my work. I would like to put stones in a 1500°F degree kiln for about three to five minutes as part of an enamel design.
I know that some gemstones are heat treated, so part of me thinks that the stones will be ok… I also know from Boy Scouts that putting some stones, sandstone especially, in fire will cause an explosion.
My worst fear is that I open the kiln and get a shotgun blast of garnet shards in my face. Not as scary, but still high on the ‘suck factor’, is having a stone break as it is going from the kiln to the cooling rack.
Can I put gemstones in a kiln as part of my copper enameling without harm to me, my kiln or my project?
The stones that I want to use are:
Garnet
Amethyst
Opal… as in “Hi Opal” and not the amorphous gemstone prone to crazing.
CZ
Hematite cabochon
They will all be less than 1ct.in size, if that matters.
I remember hearing that some of the more precious gemstones can be “cast in place” which involves molten metal temperatures. I’m not sure, but amethyst may have been one of these. I know diamonds, rubies, and sapphires will work this way.
Upon googling, I see that molten metal temperatures may not be high enough - they recommend ~1000 degrees F, though they got successful results at ~1200-1300 F for CZs.
Melting point of cristobalite quartz is 1710°C, so you’re probably okay on the amethyst, as long as it is unflawed and don’t overfire. Hematite ranges around 1475°C to 1565°C, but it’s much much harder to spot potentially explosive flaws.
Garnet seems to have the largest range, from 1245°C to over 2000°C, depending on type. However, the typical gem garnets seem to be pretty high.
Three to five minutes shouldn’t hurt an unflawed stone, BUT the method you are suggesting is hazardous in the extreme - especially since one of the stones is opaque and hard to check for flaws. It is generally recommended that heating and cooling be done gradually, to lessen the risk of an explosion or a cracked stone.
Three different jewellers have contributed to this post, much input gained when I wanted advice on soldering silver wirework with gemstone beads. Too flawed, most of 'em.
Wowie zowie, Thank you! Two of the stones I am willing to put into harm’s way are heavily included, I hadn’t even thought of that fact. Now I sort of want to put them in just to see what they will do. :eek:
The reason I was so precise is that different elements in the mix affect melting temperatures. Cristobalite is not quite amethyst, and I am unsure about what the iron or manganese trace elements will do. You can lower melting temperatures by hundreds of degrees with the right catalyst. I just don’t know what they are for quartz - yet. Precise info for amethyst seems to be a little thin - apparently not many people are into melting 'em. The only one I found that said anything directly said amethyst melts at 480°, but scale wasn’t mentioned and the quote sounded more like hearsay than anything scientifically supported.
Precision will be obtained by me eventually, I have several pounds of amethyst I’m going to try using in ceramic glazes in another year or so, but I figured a reasonably edumacated guess was worthwhile here.
Considering the flaws in the gemstones under consideration, I hope I’ve spared somebody a nasty surprise.
