History of Heat Treating Gemstones in Sri Lanka
Heat treating in Sri Lanka dates back to hundreds of years, Rubies and pink sapphire of Sri Lanka normally have a blue tint, hundreds of years ago man discovered if they keep the stone in the fire for a few hours the blue fades off and you get a better looking red. Heat treating with charcoal only heated to about 400 degrees celcious . but this was enough to make a difference.
History has many references to the metal furnaces of uva during the 14th century Damascuss steel technology was used to make steel for weapons of war. Sadly this technology was lost in time.
During the late 1970`s there was a influx of Thai dealers who started buying geuda and milky sapphire rough, when the dealers asked what they were buying for the Thai dealers said it was for fish tanks and for Terrazzo ( Flooring system popular in the 70`s ). They bought them for a few $ per pound.
It took a while for our dealer to figure out what was happening. The Thai`s were taking stones that were being thrown away here and were heating them at higher temperatures ( 1700 – 1800 Degrees ) and turning them to fine royal blues..
By 1980`s we had started hi temperature heat treatment locally and by end 1990`s stones were coming back to Sri Lanka from Thailand as we had perfected the art of heating.
Liquid petroleum and Oxygen are combusted in a Heating chamber and the temperature in the chamber is taken to 1800 degrees , at this temperature the Alumina in the sapphires are almost at a liquefying state and some Trace elements change their state and change color, Making the stone change color depending on the trace elements present.
Eg: Iron Trace elements make the stone blue, Chromium element make the Stone red or pink depending on the percentage .
Some scrupulous dealers in Thailand found the color could be further enhanced by using Beryllium as a trace Element , In Sri Lanka , we do not encourage Beryllium lattice diffusion or any other foreign matter to be added, if a heat treater caught adding anything extra we normally do not buy stones from him. This is to discourage the use of Beryllium and lattice diffusion.
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