Rating of diamonds

Every diamond is judged according to four basic standards defining the quality and the value of the stone. These standards are called "4C":

Hodnota diamantu

Carat

The size of a diamond has the biggest impact on it’s price. The metric carat, which equals 0.20 gram, is the standard unit of weight for diamonds and most other gems. If other factors are equal, the more a stone weighs, the more valuable it will be. Gemological laboratories measure carat weight when the diamond is loose (unmounted). While it is possible to estimate the weight of a mounted diamond, the lab uses ultrasensitive scales to achieve an exact weight, measured 3 decimal places, although the third decimal place is not usually mentioned at the retail level.

Although the definition of a carat has changed over time, since 1913 the international standard has been 200 milligrams, or 1/5 of a gram. Often, jewelers describe carats in 1/4 increments.

Prices of diamonds are expressed in the trade as a price per carat. When we say that the Carat Weight has the biggest impact on the price of a diamond, not only is that true for the overall price of the stone, it is also true for the unit price per carat. That's why a 2 carat diamond is more than double the price of a 1 carat diamond.

Because round brilliant cuts follow exact standards, you can make a good estimate of the carat weight of the stone based on the stone's diameter. The following chart compares the relative sizes of stones and describes how much a round brilliant diamond of a certain size is likely to weigh.

Diamonds

Clarity

Diamond clarity is a measure, which is defined on the basis of examination of internal inclusions or external damage. Almost all diamonds contain small "imperfections" — scratches, trace minerals or other tiny characteristics, but it neither impedes the uniqueness nor affects their beauty. A perfect stone with perfect clarity, or clearness, is rare, and most inclusions that do exist in jewelry grade diamonds cannot be seen without looking at the gems through a jeweler's magnifying loupe.

DIAMONDS CLARITY SCALE
MarkingGradeDescription
Diamond clarity IF LC nebo IF Loupe-Clean nebo Internally FlawlessFlawless Diamonds reveal no flaws on the surface or internally are the rarest and most beautiful gems.Internally Flawless Diamonds reveal no inclusions and only insignificant blemishes on the surface under 10x magnification.
Diamond clarity VVSVVS1,VVS2Very Very Small InclusionsVery difficult to see inclusions under 10x magnification. These are excellent quality diamonds.
Diamond clarity VSVS1, VS2Very Small InclusionsOnly looking through a 10X loupe can pinpoint the inclusions in this category and are nearly impossible to see with the naked eye. These are less expensive than the VVS1 or VVS2 grades.
Diamond clarity SISI1,SI2Small InclusionsDiamonds with inclusions easily identified under 10x magnification. Finding flaws in this category with the naked eye is difficult. The gems in this category maintain their integrity, depending on the location of the inclusions.
Diamond clarity II1,I2,I3ImperfectDiamonds with inclusions which may or may not be easily seen by the naked eye. The flaws on the stones in this category will have some effect on the brilliance of your diamond.

Colour

Diamonds come in a range of colours from faint yellow or brown, through to very rare pinks, blues, greens and other colours known as fancies. The best colour for a diamond is no colour, i.e. a diamond that allows white light to pass through it effortlessly and be dispersed in a rainbow of colours.

The best colourless stones carry a grading allocated 'D'. From here, grades are designated letters ranging all the way through the alphabet down to Z, for diamonds which may be light yellow, brown or grey. Colour gradings are difficult compare/determine without the correct conditions and equipment.

The colour of diamonds is determined by the presence of trace elements present in the atomic structure of the diamond. The more intense the colour, the further the grading descends down the scale.

Some colours occur extremely rarely and are calssified by a different scale. Such colours may include pinks, blues, greens, amber and red. As mentioned above, these colours are called 'fancy colours', with classifications dertermined by hue and saturation.

INTERNATIONAL COLOUR GRADING SYSTEMS CHART
Marking
Colour
Description
D

Exceptional white

Slight colour detected by an expert gemmologist, but still considered a "colourless" grade. A high-quality diamond.Grade G-H: Colour noticeable when compared to diamonds of better grades, but these grades offer excellent value.

E
F

Excellent white

G
H

White

I
Slightly tinted white

Colour slightly detectable. An excellent value.This diamond may "face up" colorless when mounted, especially in white gold or platinum.

J
Slightly tinted white
K
Tinted white
L
M
Slightly yellowish

Light but noticeable yellow or brown tint. Not recommended for larger diamond stone purchases, especially in engagement rings.

N
O
Yellowish
P
Q
R
S-Z
Yellow

Cut

To value a diamond cut it is necessary to determine it’s shape and type. The cut of a diamond, its proportions and symmetry have a key influence on the diamond look and it’s sparkle. Diamonds are cut into many shapes, with the shape normally dictated by the shape of the rough diamond. This is only factor that is not dictated by nature.

When cut by a skilled diamond cutter, not only is the resultant diamond a sight to behold, but it is also better able to handle light, producing more scintillation and sparkle or brilliance. Diamonds are usually cut with 57 flat surfaces of facets. The size and location (in relation to other facets) are determined by a precise mathematical formula, designed to maximise a diamonds’ brilliance.

Diamonds cut