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Thermodynamics/Altering physical state of a gem or jewel


I hope that I have reached the appropriate section, non the less, my question is about the physical properties of a gem or jewel. I'm wondering if I applied a certain amount of heat, pressure and time, would that alter the physical state of the gem or jewel; for example, the colour, shape or even transparency.

Thank you in advance, Jonathan.

Hi Jonathon,

Heat treatment of gem stones of alumina Al2O3 (rubies, saphires and others) is very common.
It is mostly done to change and improve colour and transparency. It will not change the shape or size. Temperatures used are high 500-1200 C and times run from hours to days. Diamond being pure carbon is not subject to heat treatment as in air it may disappear in a puff of CO2. The details of such treatments are trade secrets and difficult to obtain.

I hope this helps.
Best wishes


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Thermodynamics, chemistry, chemical reactions, kinetics, chemical reaction safety, dust explosion technology, static electricity. General science.


Over 40 years experience as a practicing thermochemist in industry. Head of the fire and explosion laboratory of a major European chemical company (Ciba-Geigy). Now retired.

Institute of Chemical Engineers. Royal Society of Chemistry.

Chartered Chemist, Member of the Royal Society of Chemistry (C.Chem MRSC). Msc Sheffield.

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