Jewelry Designer of fine custom
art jewelry

Does a Diamond Evaporate?

A while ago there was a discussion on Orchid  (http://www.ganoksin.com) as to whether a diamond will evaporate if subjected to high temperatures. I took a broken diamond and while I was casting, at the same time put it into my oven and kept it at 725C for about an hour. Nothing happened, other than the diamond got a 'burnt' look. Much like when one burns a diamond because it was overheated while soldering to close to it. I then used my dental oven and heated it up to 900C  for two hours at normal atmospheric pressure and still nothing happened. Further heating at 900C in a vacuum for 45 minutes also produced no noticeable change. This included weighing the stone before and after. Then I took my oxygen-propane torch and put the diamond in a platinum crucible and heated it to the maximum that the torch can go. That did do something. The temperature is about 2800C (Ref) http://en.wikipedia.org/wiki/Propane_torch

This is the broken diamond un-heated.

And this is the diamond after being heated by the torch. Note the rounded facets. The pavilion looks like it has been flame polished, like one can do with wax or Perspex. It also became a bit smaller. 

This is the diamond upon further heating for about 5 minutes at the absolute maximum that my torch can go.

Further heating. The glassy look can be clearly seen.

My conclusion: I doubt very much that a diamond will evaporate i.e. turn into carbon di- oxide, in a kiln used for firing Precious Metal Clay or  gold lost wax casting in the short time used for those processes. But with a torch it will evaporate- eventually.

I just made a quick 'model' on my triblet. Then I pushed some busted smalls , from .02 to .05 ct, that I had into it, and 'folded' the pmc over like they say in the instructions. The six 'o' clock diamond is upside down
Then I fired it in my dental oven.

 Into the oven, wrinkles and fingerprints and all...

After 900C for two hours and ten minutes the piece gets taken out. The diamonds are still there.

This is a picture of one of the diamonds that I set upside down. I thought that the point of the culet being thin, would be exposed to a higher heat and would be the first to cook away. It did not, but seems to had cracked off. The outer tip does not have the glassy look it should As the earlier pictures show.