The Diamond Guide

The Diamond Guide

What are the well established 4C’s and why are they so significant? No two diamonds are alike, each one is unique and will vary in: carat, colour, clarity and cut. Here is a summary of how diamonds are graded and valued using the 4C's.

The Shape Of Diamonds Reading The Diamond Guide 3 minutes Next The Different Methods

The 4C’s stand for Carat, Colour, Clarity and Cut. When grading and assessing the quality of a diamond, it should be acknowledged that every factor is considered equally, to arrive at the correct conclusion, of how much a diamond is valued.

Lewins Diamond Carat


Is a unit of weight, used to measure stones. One carat is equivalent to one fifth of a gram. The higher the carat, the more the diamond weighs, the greater the value. It is important to remember, the carat weight of a diamond has nothing to do with its size. For example; two round brilliant cut diamonds, that have the same weight of 1.00ct, can vary in the size of their diameter. As one diamond might be cut more shallower, or deeper than the other. 

Lewins Diamond Colour


Colour is graded, according to the intensity of colour seen. For colourless to light yellow diamonds, the less colour seen, equates to a higher colour grade and therefore a greater value. We at Lewins, use the GIA colour grading scale, which is partly pictured above. The scale ranges from D, being the highest and most colourless grade, to Z which is the lowest grade and is where colour is most observed. Fancy coloured diamonds are graded by their rarity, desirability and depth of the colour seen, which all affects the value.

Lewins Diamond Clarity


Clarity is graded, according to a diamonds lack of external blemishes and internal inclusions. The size, number, position, brightness and nature of these characteristics, are all assessed with a 10x loupe. We at Lewins, use the GIA clarity grading scale, which is partly pictured above. The scale ranges from Flawless, being the highest grade and is where no inclusions or blemishes are detected, to I3 which is the lowest grade and is where beauty, durability and transparency of the stone has been seriously affected, by the presence of inclusions and blemishes. 

Lewins Diamond Cut


Cut is graded, according to a diamonds facet arrangement and its interference with light. There are three factors that affect a diamonds cut grade: symmetry, proportions and polish. These are all graded from: Excellent, Very Good, Good, Fair and Poor. Symmetry, refers to the accurate arrangement and positioning of the facets. Proportions, is the relationship between the size and angles of various facets, which affects the stones creation of brilliance and dispersion. Polish, is the quality of finish on a diamond, which reflects the skill of how the diamonds have been fashioned.