Glass-filled rubies are now readily available in the international market. Low quality, fractured rubies are heat-treated with additives (Pb, Bi, Ta, etc) to conceal their cracks producing an attractive and relatively inexpensive product targeting the low-end markets. Highlights:
- Natural, synthetic quenched-crackled corundums may be the starting material
- Rubies to 120+cts are now available at the market at low prices
- Treatment is not 100% stable
- Glass-filled rubies are easily identified
- Glass-filled rubies are re-treatable with beryllium and other undisclosed methods
- Some glass-filled rubies contain considerable amount of Pb and may be considered as a "composite gem"
BUYER BE AWARE: The treatment of nearly all glass-filled rubies sold in the Internet and eBay are not dsiclosed to the buyer.
GEMOLOGIST BE AWARE: Many glass-filled rubies may be confused with rubies treated with fluxes and additives other than Pb. Some gemological laboratories in Asia have issued erroneous reports on these rubies.
GEMOLOGIST BE AWARE: The typical "flash-effect" seen in these glass-filled rubies may not be observed in some rubies, due to different type of additives used.
INDUSTRY ALERT: Certain types of glass-filled rubies are re-processed by a special method which removes the Pb-filler and replacing with an undisclosed substance. The resultant appearance of these rubies are stunning. At this time, no further information is available.
Ted Themelis' public presentations on the glass-filled rubies
1. Feb.3, 2005. Special seminar organized by Gemlab and presented at Tucson Gem Week.
2. May 29, 2005. Organized by the Italian Gemmological Institute and presented in one-day session in Milano, Italy.
3. The abstract of Ted Themelis's article "Glass-filled rubies" published in the Australian Gemmologist (Vol.22, No. 8, Oct-Dec.2005) is given below:
This paper described the filling of fractured rubies with lead, bismuth, tantalum and other oxides-additives including chromophores. In December 2004 a series of experiments were performed at the author's gem treatment lab in Bangkok, using various methodologies practiced commercially in Thailand. The experiments showed that certain combination of metal oxides can effectively fill surface reaching cavities in rubies at relatively low to mid range temperatures of 900-1300 oC. Starting material consisted of rubies with surface-reaching cracks. After treatment, the cracks were filled with the clarity and overall appearance of these rubies being considerably improved. The structure of most of these fillers is amorphous, thus these rubies may be referred to as glass-filled rubies. In Thailand these treated rubies are known as ruby-star or by their alternative name pao-mai, meaning new burn in the Thai language. This treatment is easily identified with a gemmological microscope; where characteristic inclusions such as the 'flash-effect', irregular-shaped reflective platelets/voids, 'frosted' areas, gas 'bubbles' and other features are observed. Stability and durability of the glass-filled rubies may be somewhat affected due to recutting and polishing and jewellery repairs. Disclosure of this treatment is mandatory, and their selling price in the market is relatively low.
Note: The pao-mai issue is also discussed in our gem treatment training course with practical "on-hands" session.