Diamond colour is all about what you cannot see. Diamonds are valued by how
closely they approach colourlessness – the less colour, the higher their value.
(The exception to this is fancy-colour diamonds, such as pinks and blues, which
lie outside this colour range.)
GIA’s colour grading scale for diamonds is the industry standard. The scale begins
with the letter D, representing colourless, and continues with increasing presence
of colour to the letter Z, or near-colourless. Each letter grade has a clearly
defined range of colour appearance. Diamonds are colour-graded by comparing them
to stones of known colour under controlled lighting and precise viewing conditions.
Many of these colour distinctions are so subtle as to be invisible to the untrained
eye. But these slight differences make a very big difference in diamond quality
and price.
Why does the GIA colour grading system start at D?
Before GIA developed the D-Z Colour Grading Scale, a variety of other systems were
loosely applied. These included letters of the alphabet
(A, B and C, with multiple
A’s for the best stones), Arabic (0, 1, 2, 3) and Roman (I, II, III) numerals and
descriptions such as "gem blue" or "blue white." The result of all these
grading systems was inconsistency and inaccuracy. Because the creators of the GIA
Colour Scale wanted to start fresh, without any association with earlier systems,
they chose to start with the letter D—a letter grade normally not associated with
top quality. Learn more about
the history of the GIA
D-to-Z Colour Scale.
Because diamonds formed deep within the earth, under extreme heat and pressure, they
often contain unique birthmarks, either internal (inclusions) or external (blemishes).
Diamond clarity refers to the absence of these inclusions and blemishes. Diamonds
without these birthmarks are rare, and rarity affects a diamond’s value. Using the
GIA International Diamond Grading System™ diamonds are assigned a clarity grade
based on a scale that contains 11 grades.
Most diamonds fall into the VS (very slightly included) or SI (slightly included)
categories. In determining a clarity grade, the GIA system considers the size, nature,
position, colour or relief and quantity of clarity characteristics visible under
10× magnification.
- Flawless (FL) - No inclusions or blemishes are visible to a skilled grader
using 10× magnification
- Internally Flawless (IF) - No inclusions and only blemishes are visible to
a skilled grader using 10× magnification
- Very, Very Slightly Included (VVS1 and VVS2) - Inclusions are difficult for
a skilled grader to see under 10× magnification
- Very Slightly Included (VS1 and VS2) - Inclusions are clearly visible under
10× magnification but can be characterized as minor
- Slightly Included (SI1 and SI2) - Inclusions are noticeable to a skilled
grader using 10× magnification
- Included (I1, I2, and I3) - Inclusions are obvious under 10× magnification
and may affect transparency and brilliance
How did the GIA Clarity Scale come about?
Like the colour scale, GIA’s clarity grading system developed because jewellers
were using terms that were easily misinterpreted, such as
"loupe clean," or "piqué".
Today, if you buy a diamond in any part of the world, the jeweller will likely use
terms such as
VVS1 or SI2, even if her language is French or Japanese instead
of English.
Cut is the factor that fuels a diamond’s fire, sparkle and brilliance.
The traditional 58 facets of a round brilliant diamond, each precisely cut and defined,
are as small as two millimeters in diameter. But without this precision, a diamond
wouldn’t be nearly as beautiful.
In early 2005, GIA unveiled its diamond cut grading system for standard round brilliants
in the D-to-Z colour range. This system, the product of more than 15 years of intensive research and testing,
assigns an overall diamond cut grade ranging from Excellent to Poor.
Although extremely difficult to analyse or quantify, the cut of any diamond has
three attributes: brilliance (the total light reflected from a diamond), fire
(the dispersion of light into the colours of the spectrum), and scintillation
(the flashes of light or sparkle, when a diamond is moved).
The standard round brilliant is the shape used in most diamond jewellery. All
others are known as fancy shapes. Traditional fancy shapes include the marquise,
pear, oval and emerald cuts. Hearts, cushions, triangles and a variety of others
are also gaining popularity in diamond jewellery.
As a value factor, though, cut refers to a diamond’s proportions, symmetry and polish.
For example, look at a side view of the standard round brilliant. The major components,
from top to bottom, are the crown, girdle and pavilion. A round brilliant cut diamond
has 57 or 58 facets, the 58th being a tiny flat facet at the bottom of the pavilion
that’s known as the culet. The large, flat facet on the top is the table. The proportions
of a diamond refer to the relationships between table size, crown angle and pavilion
depth. A wide range of proportion combinations are possible and these ultimately
affect the stone’s interaction with light.
The distance from the bottom of the girdle to the culet is the pavilion depth. A
pavilion depth that’s too shallow or too deep will allow light to escape through
the sides or the bottom of the stone. A well-cut diamond will direct more
light through the crown.
Diamonds and other gemstones are weighed in metric carats: one carat is equal to
0.2 grams, about the same weight as a paperclip. (Do not confuse carat with karat,
as in "18K gold," which refers to gold purity.)
A carat is divided into 100 points. For example, a 50-point diamond weighs 0.50
carats. Because even a fraction of a carat can make a considerable difference in
cost, precision is crucial. In the diamond industry, weight is often measured to
the hundred thousandths of a carat, and rounded to a hundredth of a carat.
How did the carat system start?
The carat, the
standard unit of weight for diamonds and other gemstones,
takes its name from the
carob seed. Because these small seeds had a fairly
uniform weight, early gem traders used them as counterweights in their balance scales.
The modern metric carat, equal to 0.2 grams, was adopted early in the 20th century.
Today, a carat weighs exactly the same in every corner of the world.