Diamond
Education
To start
with some clarification about diamond certificates. The
two biggest laboratories in the world are GIA and EGL.
Both of these are reputable with the main difference
being that GIA applies a stricter grading system where as
the EGL approach is “softer”. This may result in the same
stone obtaining a different grading from the two
laboratories. GIA might grade the colour of a stone as
“H” where EGL might grade it as “G”or GIA might grade
the clarity of a stone as “SI2” where EGL might
grade it as “SI1”. Both these laboratories grade stones
according to there own master set of colour stones
and clarity rules. This difference is also reflected in
the price of the stone. A stone with a softer grading
will carry a bigger discount than a stone with a stricter
grading which equal out the playing
field.
Colour and
clarity grading is an opinion of humans grading the
stones and not and exact science. The same lab might at
different times (with different employees) grade the same
stone differently.
However, on
the most important part of the grading report both
laboratories are exactly the same. The proportions of the
diamond i.e. the table width, total depth, crown and
pavilion angles etcetera are an exact science and are
measured and calculated using sophisticated measuring
instruments.
These
proportions of the diamond determents the brilliance of
the stone and therefore should be ideal. An ideal
cut “H” is a much better stone to buy than a poorly cut
“F”
Round Brilliant: The most common style of
cutting both diamonds and colored stones. The standard round
brilliant consists of 57 facets; 1 table, 8 bezel facets, 8
star facets 16 upper-girdle facets on the crown; 8 pavilion
facets, 16 lower girdle facets; and usually a culet on the
pavilion. Modifications of the round brilliant include such
fancy shapes as the marquise, half moon, pear shape and many
others.
Princess: Is a
relatively new shape and generally has 70 to 76 facets (no
culet). Normally it is close to a square shape (+ or - 10%),
but may come in elongated versions. Watch out for girdles
which are extremely thin and thus prone to chipping. Typical
length-to-width ratio: 1 to 1.00-1.10.
Pear: A variation
of the Brilliant cut, combining the Round and Marquise cuts,
with 58 facets to only 56 facets (when the pavilion facets
at the head and tail are eliminated). Shoulders should have
a gently but distinctly rounded arch. Common length-to-width
ratio: 1 to 1.50-1.75.
Oval: A brilliant
style of cutting very similar to a Round except it is
elliptical. It was invented by Lazare Kaplan in the early
1960s. Oval brilliant usually has 56 or 57 facets. Beware of
uneven or high shoulders (they should have a gently but
distinctly rounded arch). Typical length-to-width ratio: 1
to 1.30-1.65.
Marquise: This
shape has a boat shaped girdle with 57 facets. The shape and
placement of the facets is of the brilliant type. The name
"Marquise" came from a legend of the Marquise of Pompadour
that the Sun King wanted a Diamond to be polished into the
shape of the mouth of the Marquise. Look for uneven "wings"
or undefined points. Typical length-to-width ratio: 1 to
1.75-2.25.
Emerald: A form of
step cutting. It is usually rectangular but sometimes may be
square, in which case it is known as a square emerald cut.
It has rows (steps) of elongated facets on the crown and
pavilion, parallel to the girdle, and with corner facets.
The number of rows of elongated facets may vary, although
the usual number is three on the crown and three on the
pavilion. Inclusions are slightly more visible in "step-cut"
shapes relative to "brilliant styles. Look for too narrow or
missing corners. The beveled corners protect the stone and
make it easier to set. Typical length-to-width ratio: 1 to
1.30-1.70.
Radiant:
Rectangular or square stone with cut corners. The original
patented cut has 70 facets but it is readily available in
modified versions with 62 to 70 facets. Typical
length-to-width ratio: 1 to 1.20-1.50 for the rectangular
stones.
Heart: Look for
uneven or flat "wings" or too shallow cleft. Typical
length-to-width ratio: 1 to 0.90-1.10.
Trillion: Popular
choice for side-diamonds to enhance center diamond. Typical
length-to-width ratio: 1 to 0.90-1.10.
Cushion: Evolved
from the 'Old Mine Cut' that was developed before the turn
of the century. It is square to rectangular cut with rounded
corners and 58 facets and is characteristically with large
facets, depth, and an open cutlet (the tip on the bottom of
the diamond).
The four main
factors which determine the value of the diamond
are:
-
Size (Carat
Weight)
-
Cut
-
Color
-
Clarity
They are often
referred to as the "Four C's".
Carat
weight:
A diamond's weight
is expressed in carats. Carat weight is the easiest of the
four C's to determine. To get the exact weight, however, the
diamond must be loose. One carat is divided into 100
"points" so that a diamond of 50 points is described as a
half carat in size, or 0.50 carat. Within common weight
ranges, there is little or no variation in per-carat
price.
Cut:
The cut of a
diamond wich is also referd to as its facets relates to its
proportion. Many cutters choose to sacrifice some of the
diamond's beauty to produce a stone that is a larger carat
weight. Cut, more than any other quality aspect, gives the
diamond its sparkle. A diamond gets its brilliance and
scintillation by the cutting and polishing of its facets,
allowing the maximum amount of light that enters through its
top to be reflected and dispersed back through the top. With
proper cutting the light passes through the top, bounces off
the sides, and then travels back out the top, giving the
diamond optimum brilliance. If the diamond is cut too deep,
light passes through the side of the diamond. If the diamond
is cut too shallow , light passes through the bottom of the
diamond, also inhibiting maximum brilliance. Two popular
overall proportion indicators are Total Depth Percentage
(D%) and Table Percentage (T%) . D% is the diamond's depth
expressed as a percentage of its width (average diameter for
rounds). T% is the diamond's "table" width expressed as a
percentage of its overall width (diameters for rounds).
Round diamonds with cutting proportions within the range
generally considered attractive have depths from 55 to 63
percent. The table size of most round diamonds lies between
56 and 64 percent . With non-round shapes ("fancy" shapes),
much greater proportion variations are encountered. In most
fancy shapes, higher D% and T% are more common and are
dependent on width to length ratios.
Round Facet Diagram
Color:
Diamonds come
naturally in almost every color of the rainbow. However,
most people prefer diamonds in the white range. Colorless
diamonds are more valuable, because they are rarer and their
lack of color, or whiteness, in a diamond that allows the
light to pass effortlessly through the stone and disperse
that beauty back to the observer. The color grading scale
established by the GIA (Gemological Institute of America)
varies from D (totally colorless) to Z (light yellow). D
through F are virtually colorless. G, H and I diamonds
appear colorless when mounted. J, K and L diamonds look very
nearly colorless, but you can see some color in larger
stones. Beyond M, most people can see color pretty easily.
The color of the metal in a mounting can either mask or
enhance the diamond color. Yellow gold makes slightly yellow
or brown diamonds appear more colorless. White mounting
(gold or platinum) makes the color more perceptible.
Color Diagram
Fluorescence :
Fluorescence is not
formally a color grading term. Many diamonds glow when
exposed to light which contains relatively high amounts of
ultraviolet. This is due to a natural interaction between
the light's energy and the atoms in the diamond. Some
diamonds (about 10%) fluoresce strongly enough so as to be
somewhat noticeable in regular (incandescent) light. Strong
fluorescence in colorless to very near colorless grades (D
through G) sometime can give the diamond a hazy appearance.
Generally, for very light yellow color diamonds,
fluorescence is considered to be beneficial since it makes
the diamond appear whiter. The beauty of any diamond that
exhibits 'faint' fluorescence is not adversely affected in
any way
Clarity:
Clarity describes
the clearness or purity of a diamond. This is determined by
the number, size, nature, and location of the internal
(inclusions) and external (blemishes)
imperfections.
How to estimate
the weight of a diamond
| Rounds =
..........................Diameter x Diameter x
Depth x .0061 |
| Ovals =
..............................Length x width x
Depth x .0062 |
| Princess Cuts
= ..............Length x width x depth x
.0083 |
| Heart Cuts =
...................Length x width x depth x
.0059 |
|
Triangle Cut =
...............Length x width x depth x
.0057
|
|
Emerald Cut =
...............Length x width x depth x
factor:
Factor........Length to width ratio
| .0080 |
1.00 :
1 |
|
.0092 |
1.50 :
1 |
| .0100 |
2.00
: 1 |
| .0106 |
2.50 :
1 |
|
|
Marquise Cut =
.............Length x width x depth x
factor:
Factor........Length to width ratio
|
.00565 |
1.50 :
1 |
| .00580 |
2.00 :
1 |
| .00585 |
2.50
: 1 |
| .00595 |
3.00 :
1 |
|
|
Pear Cut =
......................Length x width x
depth x factor:
Factor........Length to width ratio
|
.00615 |
1.25
: 1 |
| .00600 |
1.50 :
1 |
| .00590 |
1.66
: 1 |
| .00575 |
2.00 :
1 |
|
| 
