GAAJ Lab. ALERT 1

GAAJ Lab. ALERT

2004.03.15

Lead glass filled Ruby

Research Laboratory, Gemmological Association of All Japan

　 We encountered a ruby which showed flash effect from fissures and fractures. Our analysis revealed that the stone was filled with lead based glass. This report describes details of the material.

　 Treating diamonds by impregnating its cleavages or fractures with highly refractive glass to improve the clarity (transparency) has been commonly known. This type of treatment appeared on the market around 1987 and has been called glass “filling” in overseas. It also is called “Koss” treatment or “Yefuda” treatment, named after the treaters. Cleavages and fractures in these treated diamonds show rainbow-coloured unique light called flash effect. This optical effect is caused by the difference of dispersion between diamond and the filled material, but refractive indices of the two materials should be almost overlapped. In other words, a host gemstone and an filled material should have very close refractive indices and different dispersion to show flash effect.
　 This flash effect recently started to be seen in some faceted ruby. Shown in the Photo-1 is a 13.220 ct ruby, whose internal features, spectral analysis and other tests indicated that the stone have 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, odd blue to purple light effect (flash effect), which was different from ordinal interference of thin film, was observed (Photo-2). Residues from heating process may often be seen in fractures and cavities in ruby, but they have far more low refractive indices than ruby. Thus, it never produces flash effect. Flash effect seen in ruby indicates that the stone is filled with substances whose refractive indices overlap with that of ruby. To identify the substance and to confirm the degree of the filling, we performed an X-ray test and X-ray fluorescence analysis. The radiograph is shown in the Photo-3. Many white streaks in high contrast correspond to distributed fracture developed in ruby. Uniform white part in radiograph indicate existence of elements which have larger atomic mass than the host ruby (Al₂O₃).
　 Figure-1 shows the results of measurements on the surface-reaching fractures by X-ray fluorescence analysis. In the results, detection of Pb (lead) other than the main chemical element of ruby, Al, and common trace elements, stands out. Existence of light elements such as boron cannot be denied at present stage, because the X-ray fluorescence analysis cannot detect those light chemical elements.
　 From the observation and analysis described above, recently appeared ruby showing flash effect must be highly fissured or fractured ruby from Africa and other origin, which have been filled with lead based glass having similar refractive index with the purpose of clarity improvement.

Photo-1：

A 13.220 ct ruby filled with lead-based glass.

Photo-2：

Flash effect is seen from fissures and fractures.

Photo-3：

A radiograph. White streaks in high contrast correspond to the distribution of fractures.

Figure-1：

Results of X-ray fluorescence analysis on fractures.

For further information, please contact:
GAAJ Research Laboratory
E-mail: research@gaaj-zenhokyo.co.jp

Research Lab. Report

2004.12.21

Lead Glass filled Ruby -update-

Research Laboratory, GAAJ : Hiroshi KITAWAKI, Ahmadjan ABDURIYIM, Makoto OKANO

　　Rubies that have been improved their clarity by lead glass filling are rapidly widespread recently. Many of permeated fractures of these rubies do not show flash effect that once had been uniquely seen in permeated material. This type of treatment now is also seen in jewellery with a star ruby or a necklace with beads. Details of the treatment are introduced here.

　　As it was reported on the May 2004 issue of this magazine, a new treatment on ruby to improve its clarity by filled lead glass that has RI close to ruby started to appear on the market. The new treatment spread out rapidly after December 2004, and many cases of serious condition have been reported from overseas as well as domestically.
　　The filling treatment that has been already reported shows flash effect (blue to purple unnatural light-effect that is different from ordinary interference of thin film) in a faceted ruby (photo 1). Also observed is a gas bubble trapped planate in a filled fracture (photo 2 and 3).


Photo.1:filling treatment showing flash effect	Photo.2:planate gas bubble trapped in a fracture

Photo.3:large gas bubble trapped in a fracture

　　Residues from heating process are often seen in cavities or fractures of a ruby, however, they have far lower RI than ruby and therefore no flash-effect is seen. Flash effect indicates filling on ruby with a substance that has close RI to ruby. By an X-ray fluorescence analysis, Pb (lead) was detected from a surface-reaching fracture, and by LA-ICP-MS analysis, B (boron) in thousands ppm order was detected.
　　Recently, a new type of filling treatment, which shows no flash effect, is dramatically increasing. Shown in a photo 4 are star rubies treated with lead glass filling. Faceted rubies that previously reported have all been heated to improve their colour. On the other hand, these star rubies show no evidence of heating under high temperature aiming at improvement of colour or asterism. They also show no flash effect on their fracture, but a few gas bubbles left as planate indicate the filling treatment (photo 5).

Photo.4:

star rubies with filling treatment
(4.888ct, 3.720ct)

Photo.5:fracture that shows no flash effect

This type of filling on star rubies has been increased recently, but GAAJ had confirmed the treatment in May 1997 and the treatment process itself was not a new technique.
　Shown in the photo 6 is a necklace of ruby beads. Each ruby is in the size of about 4×3 mm, almost all of which showed an indication of filling treatment. Photo 7 shows the observation of reflected light from them, in which surface-reaching fractures appear slightly less reflective. Radiographs of these stones are shown in the photo 8. Many white streaks in high relief correspond to fractures developed in rubies. Uniformly white part indicates that existence of elements that have greater mass than the host ruby (Al2O3), and elemental analysis revealed that the part coincides with filled lead glass.

Photo.6:

a necklace of bead with filling treatment

Photo.7:

observation of reflected light; filled part shows lower relief　

Photo.8:

a radiograph; streaks in high relief correspond to filled fracture.

　　Traditional type of filling treatment that produces flash effect on a stone was proved to use lead glass with high purity by analyses with X-ray fluorescence and LA-ICP-MS, while the recent filled material with no flash effect (with slightly lower RI) is a lead glass containing Si and Ca of about several percents and Na, K, B and Li of thousands ppm.
　　Filling treatment on ruby with lead glass for clarity improvement has been widely seen since last year. Among these stones, the treated stones with no flash effect may pose difficulty to its identification visually. In such a case, the stone should be confirmed with a radiograph or X-ray fluorescence analyses.