Welcome to AGTA GTC's Laboratory Update for September 20, 2005

In this message

  1. Glass-filled Star Ruby
  2. Meet Our Staff: Min Htut

Current turnaround time at the AGTA GTC
5–7 Business Days

Glass-filled Star Ruby

A 38.93 ct translucent red star ruby was recently submitted at AGTA GTC for identification (Figure 1). The gem was identified as natural corundum (star ruby) by the inclusions, refractive index and visible absorption spectrum.

Glass-filled star ruby

Figure 1.
This star ruby turned out to be treated by filling its fractures with a lead glass. Note the rhombohedral parting planes, which were also filled with a lead glass. (Photo: Min Htut/AGTA GTC)

However, the piece contained surface reaching fractures, parting planes and a cavity at the bottom filled with a glassy substance. The glassy filling on the bottom showed a lower surface luster than the corundum (Figure 2) and contained gas bubbles (Figure 3). No gas bubbles were noticed in filled fractures.

Figure 2.
On the polished bottom of the star ruby in question, certain areas were found showing a lower luster and hardness than the surrounding ruby. These areas proved to be glass of high lead content. (Photo: Garry Du Toit/AGTA GTC)

Figure 3.
Within the filled cavities on the base of the star ruby, spherical gas bubbles were observed. Gas bubbles were not found in the glass-filled fractures. (Photo: Garry Du Toit/AGTA GTC)

A brownish reaction was observed in the same areas under short-wave UV.
     Chemical analysis by Energy Dispersive X-Ray Fluorescence (EDXRF) showed a composition typical of ruby. However, also found were elevated levels of lead.


Figure 4.
When bombarded with x-rays, the ruby in question displayed certain areas that showed lower x-ray transparency. These appear white in the above radiograph and correspond to fractures and parting planes filled with a lead-rich glass. (Photo: Riccardo Befi/AGTA GTC)

An x-ray radiograph performed on the ruby revealed numerous white filling areas (Figure 4).
     Glass-filled rubies with a lead-glass filler have become commonplace in world gem markets since March of 2004. Similar to the Yehuda treatment of diamond, the refractive index of the glass closely matches that of the surrounding gem, thus masking cracks, fissures and surface cavities.
     Most transparent rubies fracture filled with lead glass show a pronounced blue flash effect when examined in the microscope. However, the flash effect was not observed in this gem, thus underlining the importance of careful visual examination and chemical analysis when dealing with heavily-included rubies and sapphires.
     In addition, because the temperatures for this treatment are relatively mild (400-1000° C), many of these gems will not show signs of heat treatment.

Further reading
GAAJ Research Laboratory (2004), GAAJ Lab Alert: Lead Glass Impregnated Ruby.
Pardieu, Vincent (2005) Lead glass filled/repaired rubies.


Min Htut – Gem Photographer
A native of Myanmar (Burma), Min Htut graduated with a Bachelor degree from the University of Rangoon. Soon after gaining Diploma in French and Certificate in Diplomatic Skills, he worked as Administrative Assistant for Mercier Developpement, a French firm and sub-contractor of TOTAL Oil Company for four years. He later served as Administrative assistant and Translator at the French Embassy's Consular Section in Rangoon for four years.
     Min Htut joined the AGTA GTC in June 2002. Despite having no previous experience, Min Htut taught himself digital photography and is now our resident Photoshop Wizard, being responsible for the beautiful gemstone images that grace our ID and Origin reports. He is also detail oriented, and so does much of the proofing of our reports, catching typos wherever they might lurk.

Min Htut

The AGTA Gemological Testing Center provides the industry and the public with a complete range of lab services, including gemstone identification, origin determination and pearl identification. Located in New York City, the laboratory is equipped with the latest, technologically advanced, investigative equipment.The AGTA GTC is committed to providing excellent service, superior value and outstanding quality. A complete list of services and detailed pricing information is available on our website, www.agta-gtc.org. Please contact us with any questions.

American Gem Trade Assocation Gemological Testing Center
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