Cuts & Proportion of Blue Diamonds
Like near-colourless diamonds, fancy diamonds need to be cut accurately in the best proportions to achieve maximum brilliance, sparkle, and to bring out the best of their colour. We believe cut and proportion is more important for fancy coloured stones than for near-colourless ones.
A short word with a lot of meaning.
Not all jewellers know what they mean when they talk about "cut" or that the word can be used quite ambiguously to mean at least two different things.
Cut can be use to mean:-
We discuss shape on it own page.
Proportion and Polish
"Rough" diamonds, as they are mined or found, do actually look very rough, and need to be enhanced by shaping them using various methods, the process often known as cutting or polishing.
In practise, there are many different parts to creating a finished, ready-to-set, diamond from a piece of "rough".
Cleaving is literally to cleave or part a stone along natural grain boundaries, in the way one might chop a piece of wood along its grain, but not across the grain.
Sawing or cutting is performed across the grain of a stone, and is done using a thin toothless circular saw blade which is impregnated with diamond dust. It is the diamond grit or dust which performs the cutting action.
Polishing involves grinding surplus diamond away to leave the facets. Most of the work done, and weight removed from a rough diamond is done in this way.
Bruting involves rubbing the rough diamond against another by rotating it, to make the circular shape of the finished stone. This is performed before the grinding operation.
Polish can be used to mean the actual quality of the polish which has been achieved on each of the facets.
Proportion also has multiple meanings.
The most important proportion and the easiest to ascertain is the ratio between the depth of the stone and its diameter. Ideally this should be about 58.5%, but a few percent either side of this is perfectly acceptable.
The ratio between the height of the crown and that of the pavilion is also important. The length of the pavilion facets, the size and shape of the various crown facets, the size of the table and the culet all contribute to the overall perfection or quality of the "cut."
Why Proportion Matters
Well proportioned stones reflect more light, and therefore often appear whiter and brighter than poorly proportioned stones. This can make a well cut diamond look 2 or 3 colour grades better than it actually is. Similarly, diamonds in perfect proportion may also look better than other diamonds of higher clarity, but which are not as well cut.
Diamonds which "spread" more than their weight often appeal to the less informed who believe, naively, that they are getting something for nothing. A spread stone will lack brilliance and sparkle compared with a perfectly proportioned stone. (By spread, we mean that the diameter is too great in relation to the depth of the stone, which is the same as saying that the diamond is too shallow.)
The Dealer's Cut
This often has more bearing on the price than any other meaning of "cut", and sometimes more effect than all the other 3 C's put together!
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