The GIA have suggested five grades is the largest number of grades that they believe observers could discriminate. GIA’s top grade proportions appear looser than the top grade of the proposed new AGS system; these GIA category 1 stones would likely fall within the top 3 AGS grades of 0-2. Therefore after both GIA and AGS grading systems are implemented on grading reports, it is likely that the stricter AGS 0 system will continue to achieve a sellers premium as noted in the Pricescope Diamond Grading and Pricing Survey and reflected in business to business (B2B) web listings.

Category 2

RD07

This stones has very high contrast and scintillation; it appears to have many, very small firey flashes. Also because the stone has reduced light return, its firey flashes would not be more visible than in a stone with better light return. Indeed it could be hard to sell a diamond where a personal preference for fire would influence a buyer to accept a diamond with such poor light return.

If this stone were one of the smaller samples, would the size of some of its virtual facets have been too small for the survey observers to discern the flashes? This is one of the main problems with ‘parametric’ grading systems that apply the same grade to diamonds irrespective of their size.

This stone would also display an more apparent dead zone inside the table once worn and a film of grease has covered the pavilion. This would give the stone a similar effect to that of a Fish-eye because it shows the characteristic I have previously described as a No Go Zone. I would have given this stone a lower grade.

This DiamCalc ray trace shows the flash that appears in the upper table region on the GIA photo is within a leakage region. How were the diamonds illuminated for these photo's? Was light able to enter the pavillions?This OctoNus ETAS map of reverse ray traced light return is for a model of RD07. It shows stronger than usual firey flashes on a virtual sphere. You can play with an early version of this software here. RD03 The table and upper girdle facets were said in the article to be dark; this is not evident in the photo of the same stone in G&G Fire, page 194. To test this we examined the DiamCalc light return scores which are broken down further into the table only; the ‘pop up’ window shows the table light return is very good in both static mode and when tilted through 30°.

This DiamCalc ray trace shows the flash that appears in the upper table region on the GIA photo is within a leakage region.  How were the diamonds illuminated for these photo's?  Was light able to enter the pavillions?	This OctoNus ETAS map of reverse ray traced light return is for a model of RD07. It shows stronger than usual firey flashes on a virtual sphere.  You can play with an early version of this software here.

RD03

The table and upper girdle facets were said in the article to be dark; this is not evident in the photo of the same stone in G&G Fire, page 194. To test this we examined the DiamCalc light return scores which are broken down further into the table only; the ‘pop up’ window shows the table light return is very good in both static mode and when tilted through 30°.