Pb-treated or glass-filled rubies ("pao-mai R#2") are now readily available in the 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

CAUTION: The typical "flash-effect" seen in these glass-filled rubies may not be observed in some rubies, due to different type of additives used (pao-mai R#3).
The pao-mai issue was presented in our seminar at Tucson (Feb.3, 2005) and at the Italian Gemmological Institute on May 29, 2005. It is also discussed in our ruby-sapphire heat-treatment training course with practical "on-hands" session.

Photomicrographs of various inclusions in the Pb-treated rubies and related issues are discussed in Ted's book "Flux-Enhanced Rubies & Sapphires".

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 re-cuting and polishing and jewelry repairs. Disclosure of this treatment is mandatory, and their selling price in the market is relatively low.

To view images of various furnaces and equipment used in gem treating click here