Cushion cut parametric screening

[oldminer]

Many of you know I put together screening, cut grading charts years ago which cover round and most fancy shaped diamonds. The now somewhat popular cushion cut diamond was only an old mine cut in the late 80''s when I was working on these charts and I figured it was not a shape I needed to deal with. Times and fashion change and today I get nearly constant requests for more screening tools for cushion shaped diamonds.

I find cushion shape to be the most problematic of all the shapes diamonds are usually cut into. You have square cusihions and oblong lones. You have ones with nearly flat sides and ones with rounded sides. You find thin ones and typically deep ones, but few within the sweet spot such as one finds in round diamonds. Why is this? Cushions are generally cut from a piece of rough that will give a lot better return financially and in weight when cut in other than a round or a princess cut. You get not only reproductions of old mine styles, but new, modern cut styles which mimic old cuts in symmetry and also find now super-fine cut ones which mimic H&A round diamonds. These H&A mimics while cushion shaped could make the fast obersver see a fine round stone. It is difficult to tell they are even a cushion as their light return is so good. Most cushions let the eye see their outline more readily and you know the shape is cushion instead of seeing a round looking fireball.

If one examines the round chart, the oval chart and the princess cut chart they would see certain similarities and differences. I won''t be making a cushion cut chart, but it is apparent to me that traditionally cut cushions relate more to ovalls and princess cuts when they are not square and if they are square then they must relate more to the round chart.
Diamonds which become overly deep always have a problem when I consider their cut quality. Overly deep means overly small in appearance, too. To me, that''s a basic grading bracket that no lab ought to forgive. Dangerously thin or clumsily thick girdles are always faults of either durability or allowing the stone to weigh more than it looks like it should for its diameter. Excessively large culets hur the looks of a stone. Large tables in relation to diameter are a deterrent to sparkle and fire.

Since charts are only good for screening, the principles brought out in the existing charts work for cushion cuts if the time is taken to analyze their common similarities. I sure hope this helps the many folks who are looking for these stones to locate the few really great examples that are out there. Many cushion cuts are quite small looking for their weight due to being very deeply cut. We forgive this feature with Asscher cuts, but in stones cut in the "brilliant" faceting style, experts are not so forgiving. Consumers often select a cushion which is very pretty and what I''d consider overly deep. No problem for me and if they like the stone, there is no problem for them, either. You need to look with your own eyes to make a final choice anyway.

 

[luckystar112]

This is very interesting.
In your opinion, what would you consider to be too deep on a cushion?

 

[elmo]

Good post Dave. To me there's a certain amount of black magic screening these, for just the reasons you point out. You can get length/width from the report, but you don't know if the sides are more rounded or straight, or if the culet is more octagonal or rectangular. These can signficantly affect the overall look.

I'd like to add that for those of us looking for something reminiscent of an old cut, part of the charm is the small table and tall crown. If the table is 50% and the crown height is something like 20+%, you're going to end up with a deeper stone than the charts indicate. Gotta love it!