Heated not treated stones

[Skieferins]

Hello,

As a trainee, I sometimes wonder about advanced issues....The latest quandry I have is about accidently heating a gemstone.

If I were to say, leave a Sapphire or an Emerald or even an Onyx in a setting as I expand or anneal a ring and the stone were to change colour, how can I get the stone to return to its normal colour ? Is there a shock treatment or another old fashioned way to un-darken a stone ?

I ask as I was playing with a synthetic Sapphire today and the thought crossed my mind.

Thank you in advance

[Dennis]

If I attempted to heat a stone-set piece, I would plan to protect any stone(s) with heat resistant paste or by submerging it(them) in water.

Should they be spoiled I would expect to replace them.

Unsetting stones is a preferable option and in most cases not as difficult as it first appears. Dennis.

[china]

As far as I am aware once a stone is changed with any heat treatment it can not be reversed

[Ceri]

Heating a gemstone is a tried and tested treatment for improving colour and clarity in some gemstones but can backfire if the stone is internally fractured. If you consider how most gemstones are formed, it is under conditions of heat and pressure however, the crystallisation occurs as the gemstone cools. because of the crystalline structure of a gemstone, when it is cut to shape as a gem, it can become weakened. In the same way that an experienced carpenter knows how to cut wood with the grain to prevent it splitting avoiding knots, an experienced gem cutter will do likewise with gemstones. Well cut zircons, tanzanites and sapphires are quite often heat treated and this is seen as normal and acceptable practise as long as it is disclosed. Problems arise with damaging a gemstone with heat more often if the gemstone has been fracture filled or flux healed, a practise most often associated with rubies. Gemstones treated thus suffer from thermal shock when reheated which can cause the original flaws to be exposed or worse. The Natural Sapphire Company website has some information and some pictures showing the difference heat can make. http://www.thenaturalsapphirecompany.com/education/common-treatments-for-sapphires/heat-treatment-in-sapphires/ not sure if it'll let me post the link but I've tried!