The Central Ideal

Have you heard of the ‘American Ideal’ or ‘Tolkowsky Ideal’ in diamond cutting? How about the ‘Morse Ideal’? Michael Cowing explains that because a majority of diamonds are fashioned as 57-facet round brilliants, many are familiar the ‘Ideal’ brilliant. Through their research GIA and AGS have both found ranges of angle combinations they believe retain the finest brilliance. However the two disagree over the extent of that range. Despite the controversy over these competing ranges, a surprising commonality—a Central Ideal—has been discovered, which we will explore here.

After considering the GIA and AGS sweet-spot parameter centres, along with the knowledge gained from his own research, the author concludes that the seven-parameter target ‘Central Ideal’ for the round brilliant, listed in order of importance is:

1. Pavilion main angle = 41°

2. Length of pavilion halves = 77%

3. Crown main angle = 34°

4. Table size = 56%

5. Star Length = 55%

6. Girdle size = thin to medium

7. Culet size = small to none

These proportions agree with those of many cutters of the ‘Ideal’ and diamond cutting institutions. They accord with the writer’s knowledge of the parameters that result in ideal beauty in the round brilliant.

In the final analysis, despite the differences, close agreement is found in the target centre of best round-brilliant cutting and light performance, the ‘Central Ideal’.

Click to download the pdf: The Central Ideal – published in Gems&Jewellery / April 2009 / Volume 18 / No. 2

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