Diamond Grading

Before you buy a diamond read this.

There are a few things that you need to know before you purchase a diamond. These are commonly referred to as the 4C’s. Diamonds are internationally graded according to the standards of the 4C’s. These are… Colour, Clarity, Carat-Weight and Cut. At Sinclairs we also like to include a 5th C for… Certificate.

Please Note

Goods chosen online can be paid for by phone or direct debit, if the buyer contacts the store.


The most sought after diamonds are those with no colour. Diamonds are graded by colour starting at D (colourless) through the alphabet to Z (yellow). Diamonds appear colourless but most have subtle traces of a yellow or brown body colour. They are colour graded by being compared to a set of internationally accepted ‘master’ stones.
Diamond types chart
Diamond clarity chart with grades (IF - I1)


Clarity refers to the inclusions or natural imperfections of diamonds. Virtually all diamonds contain identifying characteristics, most are invisible to the naked eye. These are nature’s birthmarks and may look like tiny crystals, clouds or feathers. Clarity is graded by using a 10x magnification loupe or microscope. Major inclusions can interfere with the path of light that travels through a diamond, affecting its brilliance, sparkle and value.

Carat Weight

The larger a diamond the rarer it is. Weight of a diamond is measured in carats (ct). There are 100 points per carat. 0.50ct = ½ carat = 50 points. While larger diamonds are highly prized, diamonds of equal size may vary widely in value depending on their qualities of colour, clarity and cut.
Diamond carat chart
Graphical representation of diamond cuts


Cut, also referred to as ‘make’, describes the proportions and symmetry of a diamond. The better a diamond is cut, the more fire and brilliance will be seen. Nature determines a diamonds colour, clarity and carat weight, but the hand of the master craftsmen releases it fire, sparkle and beauty.

When a diamond is well cut, light will reflect off one mirror like facet to another and disperse through the top of the diamond – resulting in brilliance and fire. Diamonds that are cut too deep or too shallow lose light through the side and bottom of the diamond. Poorly cut diamonds will be less valuable and brilliant when compared to well-cut diamonds.


A diamond certificate is a report that has been created by qualified gemmologists in a laboratory. The diamond is analysed under a microscope, jeweller’s loupe and other industry tools to give you a report. This report includes the diamonds colour, clarity, carat weight and cut on the certificate.

Many diamond certificates also include a diagram plotted with the diamonds inclusions. Certificates are an independent report that is proof the diamond has undergone an unbiased and professional examination, giving you peace of mind for your purchase and ensuring a quality diamond.

A GIA DiamondDossier report with a round diamond on top

Some other things you should know about diamonds.


Diamonds can come in a variety of different shapes, these include; Round, Princess, Heart, Oval, Emerald, Pear, Asscher, Cushion, Trillion, Baguette, Marquise and Radiant cut diamonds.
A chart of ten different diamond shapes

Laser Inscribed

Some diamonds are individually laser inscribed on the girdle with the brand name and unique diamond grading report number. This inscription, visible under a standard 10-power jeweller’s loupe is your proof of ownership in event of loss or theft.
Three piece of diamond with laser inscibed label


Some gem diamonds fluoresce, most commonly blue, to the concentrated long-wave ultraviolet radiation of a UV lamp. There is a perception in the trade that this fluorescence has a negative effect on the overall appearance of such a diamond.

Visual observation experiments were conducted to study this relationship. Four sets of very similar round brilliant diamonds, covering the colour range from colourless to faint yellow, were selected for the different commonly encountered strengths of blue fluorescence they represented. These diamonds were then observed by trained graders, trade professionals, and average observers in various stone positions and lighting environments.

For the average observer, meant to represent the jewellery buying public, no systematic effects of fluorescence were detected. Even the experienced observers did not consistently agree on the effects of fluorescence from one stone to the next.

In general, the results revealed that strongly blue fluorescent diamonds were perceived to have a better colour appearance when viewed table-up, with no discernible trend table-down. Most observers saw no relationship between fluorescence and transparency.