I collected some corundum (ruby/sapphire) at a gem mine this summer.  I would like to cab set or wire wrap them and incorporate them into some of my jewelry.  I have been tumbling them, but they still look greyish and not that exciting - definitely not "gem" quality, although if you look close there is almost an irridescent quality.  I have seen stones like these look neat, but I am wondering if they were heat treated?  I know that sapphires are usually heat treated to bring out the blue color.  So.... can I put my corundum into my kiln and heat treat them?  What temperature?  How long?  Quick cool or slow cool?  Will they explode and damage my kiln?  Any advice would be great!

Thanks,

Tina

 They will not go as far as explode but if the rough is cracked they will simply burst into pieces. Corundum needs one of the highest temperatures for heat treatment (that is, 1200 deg. Celsius and above). To lighten the color the heat should be performed in oxygen-containing atmosphere (reduction owens or apparented media enhance darkness whilst oxydizing produces the opposite). Heating at around 1250 celsius degr for some hours will presumably reduce some structural defects whilst adding limited color improvement; to improve color you should reach 1600-1630 degr (corundum starts to melt around 1640). An obvious difficulty: such temperatures are impossible to attain in regular kilns.

Imo you should try a 6 h heating at 1250 degr with a small piece and see if it improves with something the stone. That, if you want to afford "trial and error" methods.

 Your cool down from your melting temperature needs to be as quick as possible without forcing it then your cool down from 1200 needs to be a few days to avoid stressing the stones out and avoiding future cracking,