If the silk isn't observable then the stone was heated adequately. If the silk is partly damaged then a method known as low tube heat was employed. Low tube heat is the method where the coarse stone is heated to 1300 deg,C for 20 to half an hour over charcoal.
This takes out any grey or brown in the stone and improves colour saturation. Purple sapphires are lower in price than blue ones. Sapphires have charmed folk for millenia. They appear so encapsulate knowledge somehow, or maybe our own potential. Somewhere in a heap of filthy gravel, there's a shining gem just waiting to be exposed. Why no red sapphires? Well, they're called rubies. In the case of misty or clouded stone, heat treating will clean it up. It is presently on view at the Natural Museum of Natural History. However in terribly rare circumstances they'll be found in a clear state. Custom holds that Moses was given the 10 commandments on capsules of sapphire, making it the most holy gem. Traditional lists also name sapphire as a birthstone for Apr and the gem for the sign of Taurus. Fine blue sapphires are incredibly undervalued, asserts David Federman, US writer of Client Guide to Coloured Precious stones and other gem books.