In 1947, the Linde Company began producing synthetic star corundum by the Verneuil (flame fusion) process. Star boules were made by adding 0.1-0.3% of titanium oxide to the mixture. After the boules have cooled, they are reheated to a temperature of 1100-1500ºC for a period of several hours to several days. This causes the titanium oxide to be exsolved in the form of needles arranged in intersecting sets, just like the natural star corundum. The stones, which are known as Linde Stars in the trade are currently produced in several colors, with red and blue being the most common.
For many years they were produced in the United States and often had engraved “L” on the base of the cabochon, which stood for Linde. Today the stones are produced in several other countries as well.
Identification of synthetic star corundum is not a problem because the needles are more evenly distributed and stars appear too good. For now synthetic star is produced by the flame fusion process, and the stones show curved growth lines and gas bubbles characteristic of this process.
No comments:
Post a Comment