Buying Guide

How Diamonds are Graded

About Diamonds

The 4C’s system was developed by the Gemological Institute of America in the 1940s and 1950s to help explain the complexities of grading a diamond.

The 4C’s stand for Carat, Color or Colour, Clarity and Cut.

A carat is the unit used to measure the weight of a diamond, with each metric carat weighing 0.2 grams.

Carat weight is not the same type of carat as that used to describe the purity of gold, but takes its name from the carob seeds that were used as a balance on the scales of early gem traders.

A carat may also be divided into 100 points, with 15 points representing 0.15 carats.

The greater the weight of a diamond, the greater its rarity and value. One of the largest diamonds ever found was the priceless Cullinan Diamond, weighing 3,105 metric carats.

The most popular diamonds used in fine jewellery are white to near colourless, representing their purity.

The 4Cs scale grades these diamonds from D (Exceptional White+) to H (White), with colour and tints of yellow starting to occur at grades from I to Z.

Diamond colours need to be examined in controlled lighting conditions, but in general the less colour that a diamond has, the higher its value.

Colour GradingDescription
D, E and F Colourless
G, H, I and J Near colourless
K, L and M Faint yellow
N, O, P, Q and R Very light yellow
S, T, U, V, W, X, Y and Z Light yellow

As with other gemstones, a cut diamond may have a number of small internal blemishes or inclusions. These do not necessarily limit the beauty of a diamond and in many cases will not be visible to the naked eye.

The very best clarity grade on the GIA grading scale is a remarkable flawless diamond graded FL or F1.

The grades of VS1 or VS2 have very slight inclusions, that may be visible under a 10x magnification, and are used in jewellery offering excellent value to a discerning buyer.

Clarity GradingDescription
FL Flawless, with no blemishes or inclusions
IF Internally flawless, with no visible inclusions under 10x magnification
VVS1 and VVS2 Very very slightly included, with inclusions difficult to see under 10x magnification
VS1 and VS2 Very slightly included, with inclusions noticeable with effort under 10x magnification
SI1 and SI2 Slightly included, with slightly noticeable inclusions under 10x magnification
I1, I2 and I3 Imperfect, with obvious inclusions that are visible to the eye

The final and most important grading factor gives a diamond its dazzling qualities.

This Cut grading is also one of the hardest to judge, being dependent on how much light is reflected by the diamond (descibed as brilliance), its sparkle when it is moved (descibed as scintillation) and how it disperses light into different colours (descibed as fire).

The traditional round brilliant cut has 58 facets, with an established geometry of angles and size, but many other shapes can be exquisitely used in a variety of jewellery designs and styles.

Whatever the shape, the quality of the cut of a diamond may be graded as Excellent, Very Good, Good, Fair or Poor.