The qualIty of the Colour depended on several characteristic, these acan be the colour of the flashes, their dispersion over the gem, the pattern they produce, and more. It is complicated to determine and demands an essential quality in the grader - experience.

       In order to visualize and better uderstand this phenomenon, we decided to use the GemePro^TM Sampler to inspect the play of Colour effect of an opal gem. Since the Sampler was designed to define the body colour of gems, we didn't actually know how it would deal with the challenge this unique effect posed. However, we believed we could useful information from the flashes that would be of assistance in understanding itsgrading method.

       For this research, we received from L.Allen Brown of All That Glitters (http://www.atggems.com) images of a magnificent 8.89 ct, oval cabochon-shaped Ethiopian opal (Figure 1), which was described as displaying a "massive" play of colour effect, in a pin fire pattern. The gem was a good candidate, as it shows the effect with several different colours distributed all over the dome.

       We used a face up image of the opal and scanned it using the Sampler. Instead of retrieving an average body colour (which is useless if the flashes are part of the calculation), we recalibrated the Sampler sensitivity to be as twice sensitive to be as twice sensitive as it regularly is. By doing that, we were able to provide the main colour groups and their ratios within the overall appearance of the gem. From the resultant list, we eliminated the body colour hues and were left only with the coloured flashes.

       As seen in Figure 2, the main colours that the sampler idetified were Red(5.88%), orange(0.37%), Yellow(0.37%),, Green(1.48%), Blue (1.48%) and violet(0.37%).

      The results demonstrate the visibility of the effect and its intensity - almost 10% of the gem reflects Play of Colour fllashes, Considering the fact that the analysis was carried out on a static image, the amount of flashes in reality may even be higher. Moreover, we can see that effect is not limited to a few colours, but rather their combinations cover the entire spectrum.

       Looking at the Colour DNA (FGigure 2, left hand side), it is clearly evident that the coloured reflections are distributed all over, which means that they are spread over te entire dome. This beautiful opal has indeed earned its play of colour effect's description as "massive"