Wednesday, April 1, 2009
Can Star Rubies be Heated?
While on the subject of rubies it seems fitting to talk about a type of ruby that we all thought was impossible only a handful of years ago....a heated star ruby with leaded glass filling in the cracks. Impossible because we believed that heat melts the very silk inclusions that cause the star, thus heating would make the star disappear. Many star sapphires and rubies are heated to clarify them of silk and remove the star then they are faceted simply because faceted rubies and sapphires were often more easy to sell than star cabochons. These days the trend is turning due to the rising demand of phenomenal gemstones.
With this information on heat melting silk away, I had always stated that my star stones were unheated. In reality that was probably actually correct but I did not know that it was even possible to be incorrect. The proof of no heat was the star, I thought.
One day while in the star gem market I ran into a vendor that had no booth but was new to the market and was simply walking around showing his box of star rubies to other vendors and some were buying. I was offered to examine them and was surprised to find no fractures in these reddish purple ruby/sapphires with nice bright, obviously natural stars. Normally speaking, star sapphires will show fractures, a few or a great many, when viewed with a loupe. Only the very expensive ones will have no fractures. These were all clear and clean.
Another odd thing was that there were often more dark inclusions on the top of the stone than on the bottom, as if the cutter had chosen the wrong side to be the table.
In natural star corundum (ruby or sapphire) the star goes all the way through the crystal so if the bottom is polished it will also show a star. This means the cutter can choose which direction is more beautiful to be the face. So why did these have worse looking faces than bottoms?
Low temperature heat with leaded glass. In all heating, lighter elements rise to the top, the black spots were lighter than ruby. These gems had been heated after they were cabbed/cut, thus the dark inclusions on the top. All the cracks and fissures were now filled with leaded glass giving the gems a near perfect appearance and more translucence. The star was still there as adequate silk remained behind at these low temperatures.
These repaired star rubies have now saturated the market. Careful examination must be made to know which you have. Sometimes you can spot a bubble in the glass with your 10x loupe and sometimes you can see the 'rivers of glass' on the surface like I described in the previous story about the leaded glass filled faceted rubies. Any time you cannot see any cracks you must be sure to examine very carefully. If there is a large sum of money on the line you should use a microscope or a high tech lab.
One vendor tried to trick me with an African Star Ruby that had been enhanced with leaded glass and happened to have the same basic color of a Burmese Mogok Star Ruby. Her price was in order, a bit low for such a beauty if indeed a Mogok but the 10x loupe quickly located an obvious bubble. When I handed it back and said 'pow mai', which means 'new heat treatment', she had trouble letting go of her dream of getting big money so easily and insisted I was mistaken and tried to put it back in my hand. I asked her if she was giving it to me as a gift and she quickly snatched it back and smiled. Saving it for another less suspecting buyer, no doubt.