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Heated blue sapphires with an unusual color distribution - a work in progress

Introduction: Given the importance to the industry of this subject, we are taking the somewhat unusual step of publishing below some preliminary data on the unusual color distributions observed in some "heated" blue sapphires that are in the market place. It is important to understand the preliminary status of this data and that the team working to discover the nature of the treatment procedure continue uncovering data on a daily basis.

In December 2002 a 15ct blue sapphire was submitted to the AGTA-GTC for examination. The color distribution within this faceted stone was unusual enough for us to speculate that some treatment other than "simple heating" had taken place. A light (pastel) blue to near colorless rim surrounded a deep blue color. Viewed in various directions the boundary between the central blue color and the outer rim could be seen to be undulating.

In December 2002 we had been conducting a number of beryllium lattice diffusion experiments that eventually led the publication of our paper Beryllium Diffusion of Ruby and Sapphire (Emmett et al., 2003). Some of these experiments involved converting very dark blue sapphires of basaltic origin to a lighter blue. Additionally, in Japan blue sapphires with surface conformal colorless rims had been observed. When analyzed at the surface these stones were shown to have a high beryllium content (J. Shida, pers. com. 2003). Even though the 15ct stone was of Sri Lankan origin, our first thoughts were directed towards the possibility that this stone had been subject to the lattice diffusion of beryllium. However, although the magnesium levels appeared a little high (magnesium as a potential diffused element may produce a similar color distribution to beryllium), a surface analysis using secondary ion mass spectrometry (SIMS) did not reveal the presence of beryllium.

Following December 2002 and up to June of 2003 no more sapphires with this color distribution were observed. In June 2003 AGTA-GTC examined the next stone with these unusual characteristics and between then and September 2003 ten such stones ranging from 2 to 17ct had been recorded. Each of the stones had similar color distribution, fluorescence and infrared characteristics to the first stone. Each stone was also relatively free from crystal inclusions and healed fissures.

Following recent consultations with various dealers who have business in heated blue sapphires, a clearer picture of the number of stones with these characteristics that are on the market was determined. During searches through small and selected portions of stocks held by five dealers, 35 stones were identified. The number of stones observed with these characteristics now increases daily. We have also observed a few rubies displaying these "unusual characteristics." Further, we have discovered one stone that has been in the inventory of one member since January 2002. The general appearance of these stones is depicted in figure 1.

 
   
 
Figure 1: Six stones that show an unusual color distribution. Ct weights ranging from 3.39 to 9.54

Preliminary collected data:
The following is a "snap-shot" of the data collected thus far on these blue sapphires. As the investigation continues to provide further data we shall update this page.

Color distribution:

Information currently available from those treating these sapphires indicates that they are not being treated cut or pre-formed but rather they are being treated in the rough (with flaws cut out). This corresponds with our observations in that the color distribution does not necessarily conform to the surface of the faceted stone. The ideal conditions for observing this color distribution are created by immersing the stone in methylene iodide and illuminating through a white translucent diffuser plate. This is made more efficient when incorporated into a horizontal format microscope (figure 2). Figure 3 shows the key elements that are observed.
 
 
Figure 2: Horizontal microscope with immersion cell
 
Figure 3: One of the sapphires with unusual color distribution immersed in methylene iodide. The blue color of the central core is seen to be related to the internal diffusion of Ti. Surrounding this central zone is a fine undulating colorless line. In the outer light blue zone no internal diffusion has taken place.
 
Turning each of the sapphires to view in differing directions (figure 4) it becomes clear that the color formation does not conform with the shape of the faceted stone, (as was mostly the case with beryllium lattice diffusion). Thus supporting the information gained verbally from one person treating the sapphires - that the stones are treated in the rough. As more detail is viewed it becomes clear that a major amount of the observed color in the central core results from the "Internal lattice diffusion" of Ti from rutile inclusions. Yet little to none of this internal diffusion takes place in the outer light blue rim (See (Emmett et al., 2003) for an explanation of the probable causes). The edge of the central zone is separated from the outer light blue zone by a fine undulating colorless line.

While the stone depicted in figure 4 shows the deep blue zone to be located relatively centrally within the stone, this is not the case with all stones. Indeed this zone may vary from just, to considerably off-center. The size of the zone also varies from virtually filling the entire stone down to filling only approximately 15 - 20% (see figure 5). However, in all cases the key characteristics are clear. In discussing this color distribution with a number of colleagues from gemological laboratories worldwide each with greater than 20 years of experience, none thus far could recall seeing sapphires with these characteristics before the appearance of these stones.
 
     
     
Figure 4: A 7.5ct blue sapphire immersed in Methylene iodide. As the stone is turned the relationship of the inner and outer zones become clear.
 
     
Figure 5: The zonal features seen in these stones may vary considerably, here the central blue zone forms only a small portion of the faceted stone and it clearly its shape is not related to the faceted shaped of the stone.
 
Ultraviolet fluorescence

When bathed in Long-wave ultraviolet light these sapphires tend to fluoresce red in the areas that are light blue, i.e. the outer rims. The technique used to examine the stones is simply to hold the stones as close to the 5 watt ultraviolet source as possible while observing the stone's reaction with a 2x lens, this taking place in a darkened room - care being taken to avoid direct human exposure to the radiation. The characteristics observed correspond with information provided by J Shida as being a characteristic of basaltic blue sapphires lattice diffused with beryllium. A similar fluorescence is observed for these sapphires when laser tomography is carried out (Shida 1999)
 
     
 
Figure 6: A 2.7ct blue sapphire with a light blue rim to a deep blue core with all the characteristics of the stone described in figures 4 and 5.
 
Laser tomography

Laser tomography is an identification technique previously used only by the Laboratory of the Gemological Association of all Japan, in Tokyo. It involves the focusing of a laser into the examined gemstone while it is being held immersed in methylene iodide (Shida 1999). Under these conditions growth structures, dislocations, and other internal characteristics such as included rutile are made clearly visible. Assisting the AGTA over its concerns with these sapphires, Junko Shida the Past President and Natsuki Takahashi the current President of GAAJ, kindly arranged for and agreed to the active assistance of two GAAJ staff members, Ahmadijan Abduriyim, and Hiroshi Kitawaki, both of whom are very knowledgeable in the laser tomography techniques.

Both profile and plan views were examined of the stone in figure 4, revealing the possible (previous) presence of rutile throughout the stone (figure 8.). Also revealed is a similar, but stronger red fluorescence to that previously observed in ultraviolet radiation.
 
     
 
Figure 7:Profile and plan views of laser tomography images for one of the stones with an unusual color distribution
 
Infrared spectroscopy

Interesting and potentially diagnostic spectra in the infrared were produced for each of these blue sapphires with a light blue to colorless rim. In particular a broad band centered in the region of 3064cm-1 was recorded. Further peaks were noted at 3188 and 2626cm-1. Some but not all stones also contained the 3310 hydrogen peak. Much needs to be done in this area of our investigation before we fully appreciate the significance or otherwise of these additional features
 
Figure 8: Sample infrared spectra that show a wide band centered in the 3064cm-1 region, characteristic of this "new treatment procedure".
 
Chemistry

In order to better understand the chemistry of these stones, one example was obtained and sawn into two parts. The color distribution in this faceted stone was not surface conformal but clearly there was a deep blue center and a colorless to very light blue outer region. Using in-corundum standards with SIMS a cross-section of one half was analyzed from edge to center to edge. The results show a number of elements in a much higher concentration at the edge of the stone than in the center, these include Mg, Ti, Fe, Ga, and Si.

Further data was gathered on the other half using NIST glass standards together with the LA-ICP-MS that is located in the Gemmological Association of all Japan, Tokyo. Similarly, peculiar differences in the edge to center chemistry for the elements were discovered.

The significance of these differences and how they relate to this "new treatment" are presently being studied.

Work In Progress


Recently we have met with those who have been "treating" and marketing these stones and we have gained many more samples, which are presently undergoing various forms of preparation and analysis. As more data becomes available and a clearer picture of the process gained, we shall inform the industry in the most appropriate manner. In the meantime it is inappropriate to speculate beyond stating that this process does not appear to be one that we can recognize as being "normal heat treatment" and as no beryllium has thus far been found it does not appear to be a process involving the diffusion of beryllium.

The gemological team carrying out this investigation is comprised of AGTA and GIA staff members and advisors. These are John Emmett, George Rossman, Kenneth Scarratt, Garry DuToit, Donna Beaton, Tom Moses, Shane McClure, John Koivula, Christopher Smith, Matthew Hall, Wuyi Wang, Mary Johnson, and James Shigley.

Reporting Policy

Currently and until such time as these stones are fully characterized, AGTA-GTC is not issuing reports on sapphires that show the features described here. An interim letter describing the identification problem is given to clients stating that a report will be issued at a later date. Clearly, sapphires that show "no indications of heating" are not treated by this process and we will continue to issue reports on these gemstones. We shall also continue to issue reports on those sapphires that have been heated but do not show indications of having been treated by the new process.

Batch Testing Service

A batch testing service has been implemented to assist the trade separate these stones from other heat-treated blue sapphires. It should be noted that while we are continuing our research to fully understand the treatment process these sapphires have been subjected to, it is a reasonably simple gemological process to identify the sapphires that have been treated in this fashion. Stones submitted in batches will be separated into those that show the characteristics described here and those that do not. The fee for this batch testing service will be $300 per hour with a half-hour minimum. Fees for consultation on these gemstones will be charged at $400 per hour with a quarter-hour minimum.
 
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