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 Proportionscope: |
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The tool used to measure the proportions of a diamond is a proportionscope. |
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 It is necessary to
consider all the proportions and not only some of them. An angle of crown too large or too
small is indicated in remark.
An open culet indicates a poor stone (except
in the case of the old cuts).
In melee, thick rondists indicate not very
interesting stones. |
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Many professionals consider the cut the
most important diamond characteristic because even if a diamond has perfect color and clarity, a diamond with a poor cut will have dulled brilliance. |
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For those how wish more information
regarding the proportions of the brilliant cut, they will know that in 1919, Marcel Tolkowsky
published « Diamond Design » in which he describes his research on the proportions of the
brilliant cut. You can click on this link and search his work: Tolkowsky. |
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 The « ideal » cut: |
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It is a very vast subject,
which divides the professionals still today. To obtain the maximum of
brightness, fire, « life », a diamond must be cut according to certain
dimensions and proportions. The diamond cutters must carefully consider the
optical properties of each diamond to determine its optimal size. |
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Brilliance of a diamond following the proportions of its cut: |
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| Ideal cut: light
is correctly reflected. Diamond has a beautiful brilliance and « fire ». |
Too shallow: light is
lost out the sides causing the diamond to lose brilliance. |
Too deep: light escapes
out the bottom causing the diamond to appear dark and dull. |
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To obtain an ideal cut, the 3 principal elements, are: |
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1) Total depth %: |
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height of the stone is divided by the diameter in rounds or by the
width in all other shapes. Say the stone measures 6.52 -
6.56mm x 3.92mm, the
total depth is 3.92mm ÷ 6.54mm
= 59.93%. Ideal round diamonds should have a depth of 59%-62.5%. |
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2) Table percentage (%): |
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 Only round diamonds
have a standard for table size. In round diamonds for a diamond to be recognized as an ideal
cut the table must be relatively small. It must fall between 53% and 57%. |
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3) Girdle thickness: |
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 The best girdle range for a diamond to fit in the ideal cut
category for rounds is anywhere between « Thin » and « Slightly Thick ». The girdle could be
Thin, Medium, Slightly thick or any combination of the three, such as « medium to slightly
thick ». The various graduations thickness of the rondist are: Extremely thin, Very thin,
Thin, Medium, Slightly thick, Thick, Very thick and Extremely thick. |
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4) Others...: |
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 Other elements are
important, such as the culet size. The culet size is listed on a
certificate and your diamond’s culet should be pointed (no culet),
very small, small or medium because these are not visible to the
naked eye. The graduations of the culet size are: No Culet, Pointed,
Very Small, Small, Medium, Large, Very large and Extremely large.
Avoid the culets equal or lower than « Large » which when you look at
diamond by the table are very visible with the naked eye. |
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 The girdle of diamond
can be faceted, polished or rough. Diamonds which has a very beautiful
cut have often the faceted girdle. A diamond cutter must work from
additional time to facet it, which is not always economically
profitable. A faceted girdle does not improve quality of diamond. The
GIA evaluates only the thickness of the girdle and not its appearance. |
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Diamond Shape and Cut
