Applications- Gemstone heat treatment

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Gemstone heat treatment

Gemstone treatment

In many countries, Linn furnaces are used for improving the characteristics of gemstones.Focus is put on the thermal treatment of sapphires and rubies. Rubbies are mostly treated on air at temperatures of up to 1820°C. Our furnaces VMK-1800 and VMK-1800-G are well suitable for this application.

A specialty is our Rubi-Star range with furnaces of up to 1820°C which allow heat treatment with pure oxygen with pressures of up to 60 bar. Advantages are faster diffusion of oxygen and suppression of cracks caused by expanding inclusions during heating.

Furnaces for treatment of rubies can furthermore be used for brightening up of too dark sapphires.

For heat treatment of sapphires, varicolored sapphires (fancy sapphire) and Geuda qualities under reducing atmospheres, HT-1800 furnaces with a useful volume of 3-22 l are used. Due to heating elements made of molybdenum or tungsten and special insulation, heat treatment of up to 1750°C under hydrogen is possible. Therefore, the furnaces are equipped with the necessary safety devices (gas feeding device, burning-off device, safety package and gas sensors).

Inductive heating units with MFG- or HTG-generators with exchangeable crucibles respectively susceptor materials (W, MoSi, C) with ceramic fiber or stone insulation allow temperatures of 1850°C with oxygen as well as with hydrogen atmosphere.

Other gemstone heat treatments, for example color improvement of tanzanite, transformation from amethyst to gold topaz, aquamarine, zirconium require only simple furnaces of up to 1200°C. Suitable for that are our furnaces of the range VMK-10 – VMK-250 and LM-111 – LM-512.