Recently a parcel of 7 faceted rubies, ranging from 1.020 to 1.228 ct, was submitted to the IGE's Analyses Laboratory for its identification. According to information supplied by the dealer, the rubies were purchased directly from a cutter in Bangkok.
A preliminary observation, revealed the presence of a large number of flux appearance inclusions and a strong fluorescence to long and short wave ultraviolet radiation which seemed to indicate a synthetic material. A detailed examination, however, proved the natural origin of the samples and a treatment by which their fissures and cavities had been filled with a foreign solidified substance. Most surprising was that this substance is basically composed of an aluminum and sodium phosphate with small quantities of silicon, titanium, iron and calcium.
It is not the first time that the presence of this strange type of glasses is mentioned as filling fissures. In ICA's Laboratory Alert Number 56 (1992) this author notified his observation of a similar treatment in a rough non-transparent ruby crystal of intense color.
In fact, the novelty of the news laid in the compositional characteristics of the glass that covered the crystal and filled its cavities and fissures, showing a high content in phosphorous and sodium, especially in the glass that coated the surface.
In the gem quality rubies subject of this note, chemical point analyses (SEM-EDX) were performed on the filling of a large external, irregular cavity present in one of the samples, and in a number of minute external cavities forming part of veils of communicated channels found in all the rubies.
The comparative table enclosed, shows the results of the rough crystal studied in 1992 and some of the results obtained in the gem quality rubies.
It seems evident that the sample studied by the author in 1992 was the result of early attempts of a new treatment, which is being applied today to gem quality material.
It is known that fracture filling can be produced intentionally or accidentally, the later as consequence of the fusion of material that is in contact with corundum (silica, aluminum silicates, borax, etc) during heat treatment processes. The exact nature of the material used in this case is unknown. Nevertheless, the chemical composition of the filling suggests a sodium ammonia phosphate-type substance and the intentionality of the process.
In a near future, a more detailed study about this type of glass-like fillings will be published along with optical and electronic images.
Source: Instituto Gemologico Espanol, July 20, 1995