However, with the 'average' or 'good' cut to fixed proportioned diamonds, these parameters have been extended in order
   to add possibilities.
The diamonds cut to within these parameters will not sparkle as much, will lose their sparkle more quickly and when
   produced will cost, therefore, less as they would have lost less rough diamond weight during the cutting process.
Actual visual size may not be affected as both 'thickish' and 'spread' stones can suffer from these extended parameters.
They are or rather should be discounted to the consumer who should be made aware of what he/she is actually
   purchasing.
The diamond report (certificate) will not mention these 'nuances' within the 'very good' range of parameters but should
   mention whether the proportions are 'good', 'very good' or 'unusual'. In fact many GIA certificates will not show either the
   crown height or the pavilion depth, just showing the total depth, which, is a useless parameter. This is, to say the least,
   quite misleading to the client.

What are 'ANTWERP', 'PREMIUM', 'IDEAL' or 'H & A' CUT DIAMONDS

Firstly you must understand that we do not, here in Europe, in the trade, use the terms 'premium' or 'ideal', we use the term 'very good' in order to identify them.
The term 'good' would be used as ' average' cut and the term 'unusual' in order to identify a 'poorly' cut diamond.
Now within the term 'very good' there are various types of cut diamonds all cut to within certain fixed parameters. The whole idea is that these parameters all
   'work' with one another, in reality they 'work' in different ways.
You can have a 'very good' cut diamond, within the 'very good' parameters which will look different to another, of identical weight which has also been cut to
    within these fixed parameters.
You will now understand that the differences are subtle, only a professional, using his trained eye will be able, using the appropriate magnification and lighting
   conditions, to tell the differences.
Having said that there are also very noticeable differences as well within this 'very good' parameter range.
Some diamonds which are cut to within 'very good' proportions are cut 'to weight'. Cutting to weight is a term used by professionals to identify a diamond cut in
   order to lose the minimum amount of rough material.
This presents the diamond with a small table, around 56% to 57%, a thickish girdle, around 4% to 4.5% and a high crown height, around 15% to 16%.
These diamonds will all have very good light refractive qualities but this is not, to our mind, what is most important. See Ideal cut and Hearts & Arrows.
What is important is the actual 'look' of the diamond on the finger.
This 'look' must bring together both very good sparkle and very good actual visual size to weight ratio. Indeed some of these 'cut to weight' diamonds look much
   smaller, at equal weight, than other not 'cut to weight' ones.
These very well 'cut to weight' diamonds have, through the decades, found their way to the US market, reasons being that they were cheaper to produce and the
   US customer knew no better and was talked into believing that this was the best, but who are we to argue with this as we produce 'cut to weight' diamonds
   which are sold to our US clients.
In Europe, we and our clients, know that it is not, our European clients look for what is called, in the trade, as the 'Antwerp' cut, the Americans have labeled their
   'built up', 'cut to weight' stone, the 'ideal' cut or 'Premium' cut in some instances and the Hearts & Arrows cut shows this to the extreme as it is small looking.
Both these cut to fixed proportions stones have very good sparkle, but to the eye, there are appreciative differences.
I have been talking about 'very good'(premium) cut diamonds, which I must add, as the differences in cut are very subtle, will not influence the price very much.

For more information please click on the link below:

http://www.professionaljeweler.com/archives/news/2004/020704story.html

For Hearts & Arrows: Click here

For more on choosing your diamond click here

Always happy to answer any further questions on this subject.
George Zaidmann
Certified Gemmologist
Expert diamond appraiser
Member of the Antwerp Diamond Bourse since 1972