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.
EGL grades colour according to the international scale of D
to Z. Every letter on the scale represents a
range of tone and saturation.
Two diamonds belonging to the same colour range can
actually differ in their depth of colour. Since
brightness and fire, which are the result of good proportions, can affect a diamond’s colour, it is important
to grade a diamond not only face down but also face up as diamonds are typically set and worn face
up.
In the face up position, diamonds with moderate or distinct
fluorescence have a better colour than less fluorescent ones.
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 |
|
| 
