The attraction of fancy shapes is largely the appeal of the shape itself. Round brilliant cut diamonds are without doubt more brilliant. Generally speaking larger fancy shapes cost a little less than round diamonds. This reflects the larger yield cutters get by cutting a fancy shape that ‘fits' into an unusual shaped piece of rough.
There are no ‘ideal' fancies, but here are some tips. Expect to see a ‘bow-tie effect (usually dark but can be lighter) in the centre of longer/narrower diamonds like marquise, pear and oval diamonds.
The best tool for selecting fancy shaped diamonds is the ideal-scope .
Popular length to width ratios are marquise 2:1, heart 1:1, princess 1:1 or square and emerald cut 1.5:1.
Watch out for very thick girdles that result in paying for excessive weight. Also beware of very or extremely thin girdles and especially thin points or ends on marquise and pears. Be especially wary of princess cuts with thin girdled corners.
It is very easy to see inclusions and lower colour in emerald cut diamonds because they have a less ‘cluttered' look. The end facets are often very steep and can look very different to the side facets, it is better if they look similar.
Grading fancy shaped diamonds is very complex. The best proportion standard to date has been developed by an associate in America , Dave Atlas and his laboratory Accredited Gem Appraisers ( AGA ) and is used by the National Association of Jewellery Appraisers in America.