Treatment Of Verneuil Synthetic Corundum

Heat treatment of Verneuil synthetic corundum at temperatures of more than 1600°C can substantially reduce the visibility of curved color banding and striations (striae arise from fluctuations in the composition used for the feed in the flame fusion process). The high temperatures reached in the treatment process allow these impurities to diffuse, and become much less prominent. If the heating is irregular, with sudden temperature changes, small surface cracks can be developed at the surface of Verneuil synthetic corundums. If these cracked corundums are then packed in borax and heated once more, partial healing takes place, and some of the borax penetrates into surface fissures producing features very similar to those seen in natural ruby (Nassau). Many colored varieties of treated synthetic corundums are sold in the gem markets and mines around the world as natural. Even experienced gemologists make mistakes perceiving them to be natural.