Glass-Filled Fractures in Ruby—Like Diamond

The Sept. 3 edition of the Gübelin Gem Lab (GGL) newsletter announced that “lead-filled rubies” were entering the market. According to the newsletter, “The clarity enhancement of ruby with a lead-based filler might now be considered noted in heat-treated rubies. Heat-treated rubies filled with a lead-glass substance, intended to improve the clarity, were submitted to the lab for testing. The results on the certificate stated indications of heating, as well as a complementary comment: additional clarity enhancement with a lead-glass.”

Prior to that, the Gemmological Association of All Japan (GAAJ) and the American Gem Trade Association (AGTA) Gem Testing Center (GTC) laboratory had made similar announcements. GIA’s gem lab also recently made this same announcement.

Fracture filling is not new. Most varieties of gems can be, and have been, fracture filled. Emerald is the most commonly fracture-filled gem, and reports about fracture-filled Paraìba tourmalines have surfaced recently. But neither the tourmaline nor emerald fillers include lead glass.

But the fact that four major laboratories have sent out lab alerts regarding this clarity enhancement makes it more than a passing fad. Identification of filled ruby should be similar to identification of filled diamond. Ruby’s red body color makes the identification a bit more subtle.

As far back as 1984, ruby had been shown to have large surface cavities filled with glass. And recent studies on heat treatment of rubies, especially those from Mong Hsu Burma, show glass remnants in healed fissures. This glass results from either the addition of a flux or from natural inclusions that have been melted and cooled before recrystalization.

Abduriyim Ahmadjan, research gemologist with the GAAJ-Zenhokyo laboratory, reported to the AGTA GTC laboratory that he and his colleagues were seeing “unheated rubies … treated by a glass fracture-filling technique similar to that applied to diamonds.”

Samples sent to AGTA-GTC confirmed lead glass. Identification using the microscope and darkfield illumination shows the typical “flash effect, similar to those found within glass-filled diamonds and resin-filled emerald.”

In correspondence with JCK, Ahmadjan says that so far, “30 lead glass impregnated rubies have been [examined].” He also mentions that the number of treated rubies coming through the lab is not increasing.

However, a large 16-ct. fracture-filled ruby was submitted for a report to the AGTA GTC laboratory in June. AGTA says the trade should be aware that “rubies treated by this technique are now present in the U.S. market.”

GAAJ notes that the flash effect in ruby results from use of a material that has a refractive index (RI) very close to that of the host material.

Of one such treated ruby examined, GAAJ notes that “tests indicated that the stone has been heated and may have its origin in regional metamorphic rock such as in Africa. This ruby was faceted but many surface-reaching cracks were observed inside the stone. From these cracks [emanated an] odd blue to purple light effect (flash effect).”

GAAJ also notes that “ruby showing a flash effect must be highly fissured or fractured ruby from Africa and other similar origins, which have been impregnated with lead-based glass.” GAAJ also notes that this enhancement is done to improve clarity.

Seeing a few dozen of these treated gems in Japan and one or two in the United States doesn’t mean it’s a commonly encountered treatment. But now that GGL has begun receiving them for identification, the industry needs to become aware of it.

“We do have some pictures of the stones which show a bluish and orangey flash effect on the fissures that are filled with the Pb-based filler,” says Dr. Daniel Nyfeler, managing director of GGL in Lucerne. “In [this picture] you can see the bicolored (bluish on the left and orangy on the right) flash on the horizontal fissure. In the other picture there are several vertical filled fissures in blue colors.”

Unlike the GAAJ rubies that were heated at high temperature, the gems showing up in Switzerland were “low-temperature heat-treated rubies from Madagascar.” According to Nyfeler, GGL is planning to publish a brief article on unheated fracture-filled rubies.