This section contains basics of diamonds and explanation of
some advanced topics. We strongly recommend going through this
section. There is much more than Four C’s for analysis but they
are the most fundamental concepts for analyzing diamonds.
There has been lot of research going on for many years on
diamonds. Various universities and gemological laboratories are
continuously doing research on diamonds. Analysis of diamonds is
basically divided into four C’s. Four C’s are internationally
recognized for diamond analysis and grading. The explanation of
these four C’s is as follows.
- Carat Weight
The process of the growth of a diamond in the interior of the
earth did not occur evenly, but in several phases. In these
various phases, the conditions – pressure, temperature and
cooling – did not always remain constant and that caused
internal features, so called inclusions. These inclusions have
the major impact on diamond cost. Clarity features are
represented by internal defects inclusions and external defects.
The internal defect of a diamond cannot be removed without
All other factors being equal, defect -free diamonds are
considered the most valuable.
When examining the inclusions, it is important to observe them
through crown. Following points should be considered during
- Size and number of inclusions
- Visibility of inclusions
- Appearance of inclusion
- Nature of inclusions
- Position of inclusions
- Type of inclusion
- Influence on brilliance and durability of stone
The list of internal and external features of a diamond is as
A very small inclusion, which usually appears as a point under
the Loupe. Some specimens contain groups of pinpoints.
A long thin crystal - acicular inclusion.
Hazy or milky zone consisting of a great number of tiny
- Cracks (also called feathers)
A cleavage fracture or fissure with an irregular path inside the
stone, usually breaks the surface of the stone. Types of cracks
are as follows.
- Cleavage Cracks
These occur in the direction of the cleavage planes parallel
to the four octahedral faces. They always occur in straight
lines and the cleavage plane often shows a fine striation,
similar to that of a cleaved piece of wood.
- Fracture Cracks
These can occur in all directions and do not run along a
cleavage plane. Their direction is irregular and often
jagged. Fracture cracks are caused mainly by mechanical
means, such as pressure or a blow.
- Tension Cracks
These are caused by differential thermal expansion of an
included extraneous crystal and often into the interior from
All types of cracks, which are perpendicular to the crack
plane and appear white and feathery are termed “feathers” or
“glets”. Also small blow marks and indentation marks on the
edge of a facet are sometimes so described.
A small and shallow pit typically occurring on the girdle
edge. Some nicks may have a greater size.
A large three-dimensional opening on the surface of a polished
- Bearded girdle ("bearding")
Micro cracks extending from the girdle into the stone.
A deformation zone on the diamond surface caused by a blow.
- Crystal in crystal
A diamond microcrystal inclusion in polished diamond.
A diamond inclusion standing out against the surface of the
Smoothing of edges and vertexes mainly caused by careless
cutting. Micro cracks orientated along the edges are often
perceived as white lines rather than sharp edges.
- Extra facet
A facet present in addition to those required by a given
cutting style and which does not fit the symmetry pattern.
Part of the original natural diamond surface which is left on
the polished stone after cutting.
Micro opening which often appears as a white point.
- Polish lines
Thin parallel lines left after polishing; thin parallel ridges
within one facet caused by the irregularity of the crystal
structure; small parallel polished trenches formed by the
cutting disk surface.
- Polishing marks
Hazy areas of the stone surface caused by excess heating
(superheating) during cutting or polishing.
- Rough girdle
Feathery or cavernous girdle surface, often with micro cracks.
A linear trench, which typically appears as a thin white line
(curved or straight).
- Surface graining
Defects and distortions of the diamond crystal structure which
reach the surface of the stone and often cross facet junctions.
Clarity of the diamond is divided into
FL (Flawless): no blemishes
or inclusions when examined by a skilled grader under 10X
IF (Internally Flawless):
no inclusions when examined by a skilled grader, and only
insignificant blemishes under 10X.
VVS1 & VVS2 (Very Very Slightly
Included): Minute inclusions that are difficult to
see. In VVS1, they are extremely difficult to see, visible only
from pavilion, or small and shallow enough to be removed easily
by repolishing. In VVS2, inclusions are still very difficult to
see. Typical inclusions: scattered pinpoints, faint clouds,
slightly bearded girdles, internal graining, and tiny feathers,
chips, and bruises.
VS1 & VS2 (Very Small Inclusions):
Minor inclusions ranging from difficult to somewhat easy to see.
Typical inclusions: small included crystals and feathers,
distinct clouds, and groups of pinpoints.
SI1, SI2 & SI3 (Small Inclusions):
Noticeable inclusions that are easy (S1I) or very easy (S2I) to
see. Inclusions are often centrally located and noticed
immediately; that may be eye -visible. Typical Inclusions:
included crystals, clouds, and feathers.
I1, I2 & I3 (Imperfect):
Obvious inclusions that are often easily eye-visible faceup; in
I3, they may threaten durability. Typical inclusions: large
included crystals and feathers.
The color of the diamond is very important factor in
determining the value of the stone. The colorless diamonds are
costliest. The grading of the color is carried out with the help
of master stones. The diamond to be graded is compared to a
master stone to determine its exact color. There are very minor
variations in color shades, which is very difficult to
differentiate with untrained eye. A letter denotes a diamond
grade. The colorless diamond is assigned D and it is increased
up to Z as the intensity of the color is increased. Due to
perception ability of human's eye, even two stones of the same
color can be perceived in a different way. Hence, to ensure the
correctness of the color grading, a diamond should be examined
on both sides of a masterstone.
The cut of the diamond is one of the few things, which are in
human’s hand in making a polished diamond. Cut is very important
factor in diamond pricing because it is directly related to
diamond’s beauty. Brilliance and firing of the diamond is
directly related to its cut. The cut quality is a complex
parameter, which can be defined as a combination of Proportions,
symmetry, and polish:
Cut grading = proportions grading +
symmetry grading + polish grading
A stone shows the maximum brilliance and fire only when it’s
cutting proportions exactly correspond to those calculated from
physical and optical laws.
When analyzing the cutting of the diamond, following points
should be taken into consideration.
- Table size evaluation
- Crown angle evaluation
- Examination of pavilion facet reflections
- Girdle Evaluation
- Estimation of pavilion depth
- Estimation of culet size
- Effect of proportions on stone value
Following is the list of main
parameters of a cut diamond.
- Average girdle diameter (mm) (the mean value of the minimum
and maximum Diameter) is taken as 100%;
- Table size (% of the average girdle diameter);
- Total depth (mm and % of the average girdle diameter);
- Crown height (from the upper edge of girdle to table; % of
the average girdle
- Pavilion depth (from the lower edge of girdle to culet; % of
the average girdle Diameter);
- Girdle thickness (qualitative grading or % of the average
- Crown angle (degrees; the angle between the bezel facets and
the girdle Plane);
- Pavilion angle (degrees; the angle between the pavilion main
facets and the Girdle plane);
- Culet size (qualitative grading).
The quality of polishing is also considered in diamond cut
evaluation because the polish of diamond contributes to its
firing and brilliance.
Diamond weight is measured in carats. A carat is a unit of
weight. Carat weight is one of the most important factors in
deciding price of the stone. The weight of the diamond is taken
into consideration first when analyzing the diamond. Carat is
most commonly abbreviated as “ct”. The weight of a diamond is
generally indicated to the second decimal point. For example if
the weight of a diamond is one and quarter that means 1.25 ct.
1 carat = 0.2 gram= 100 points