Loose Diamond Quality – The 4Cs and Beyond​

Stones that have not been ethically-sourced should not be sought out, bought, or sold by any respectable company.

For some people, a diamond’s most important characteristic will simply be how large it is – but the size of a precious stone only tells a small part of the story.

Diamond dealers rate a loose diamond in a variety of ways, and the pricing process can be a complex affair. The main four characteristics considered before valuing a diamond are its cut, its clarity, its colour and, yes, its carat. While the Gemological Institute of America’s (GIA) grading system is the most common standard with which to value a loose diamond, diamond dealers will differ in their exact pricing methods.

Read on to learn more about the four principal traits that dealers consider when pricing a diamond – also known as the “4 Cs” – as well as a few other, less well-known “Cs”.


This doesn’t simply refer to the diamond’s shape, but the way the stone’s shape affects its ability to reflect light.

Dealers often consider this characteristic to be the most important. Clarity, carat, and colour can’t make up for a poor cut. If a stone is cut with the proper proportions, then light is returned back out of the top of the diamond, giving it an impressive brilliance. Alternately, if it is a bad cut then the light leaks from the sides and results in a low-level sparkle from the table.

The cut of a diamond is the most difficult characteristic to analyse, and while the light-return can be technically measured, there is also a less quantifiable human perception to consider. Measuring the cut of a diamond involves looking at the light performance it offers. This is in turn broken down into the stone’s brilliance (the human perception of its brightness), its fire (the colours a diamond shows when revealed to the light), and its scintillation (the sparkle).

The level of a stone’s cut is graded from Excellent, to Very Good, to Good, to Fair, and finally to Poor.

Clark Diamonds offers diamonds ranging from good to excellent.


This usually refers to white diamonds, and how colourless they are. A chemically-pure, perfectly structured diamond will be as clear as clean water. The less colour in a diamond, the more valuable it is.

The most common scale that diamond dealers will refer to is the GIA diamond colour chart. This ranges from colourless, to near colourless, to faint colour, to very light colour, to light colour. Diamonds at the lower end of the chart may have a yellowish or brownish tint, and will be priced accordingly, with the least coloured being valued most highly.

The colour scale ranges from D (colourless) through to Z (light).


This term describes a diamond’s flaws, which are called “inclusions”, and its surface flaws, which are called “blemishes”. The fewer the inclusions and imperfections, the more highly a diamond is valued.

Diamonds are examined for flaws under a 10x magnification.  The clarity scale should not be considered a linear scale; to the naked eye an SI2 stone can appear just as impressive as a flawless stone of equivalent Colour and Cut.  Obvious inclusions shold only start to appear at the I1 – I3 range.  An apparently low clarity stone can still be impressive to the naked eye.

The clarity grading and the subsequent value of the diamond will be affected by the position of an inclusion within the stone, as in some cases the diamond’s cut will make its imperfections harder to see.


Diamonds are sold by the carat (ct.), which refers to the weight of the stone.

One carat is equal to 0.2g. Each carat can be divided into 100 “points”, which allows for the valuer to measure a stone very precisely, down to a hundredth of a decimal place.

As the carat size of a diamond increases, both the overall value will increase, and the rate at which the value rises will increase. This exponential value rate is because diamonds become increasingly rare the larger they are; therefore, the higher the weight, the higher the price-per-carat.

Diamonds of different weights may appear considerably different in size – but not always in the manner you might expect. A well cut diamond may have a similar or even a lower carat weight than another diamond, but due to its cut the first diamond could look larger and more impressive than the heavier diamond with the poor cut.

Bonus Cs

While the 4Cs are the most well-known and generally accepted characteristics with which to price a diamond, some diamond dealers and jewellers list other Cs to consider before buying a diamond.

It’s been suggested that anyone buying a loose diamond should be confident in the reputation of the company and that they are paying the right price, and that the dealer should be able to demonstrate their commitment to a stone being ethically sourced and conflict-free. Once the stone is mounted on a piece of jewellery, some jewellers have pointed out that the creativity behind the piece will contribute to the valuation, while others say that the quality of the centre stone on a piece of jewellery will be the most important consideration, and other adornments are secondary.

Other considerations

While these secondary Cs are of course important considerations for anyone buying a diamond or diamonds, we feel that the original 4 Cs should take priority. It should go without saying that all stones should be conflict-free, because stones that have not been ethically-sourced should not be sought out, bought, or sold by any respectable company.

As buyers of loose diamonds, it’s important to be aware of the 4Cs, as they offer a deeper knowledge of the subtleties of diamond valuation. Take a look at our chart here.

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