Diamond Grading

Learn all about the Diamond 4 C's. Grading diamonds, quality assessment is essentially broken down into four main elements, cut, colour, clarity and carat weight, outlined in our online guide to diamond grading. We explain the GIA criteria for diamond grades, and how the quality of the grade can affect the price of the diamond. We explore colour grading, from colourless to tinted, clarity grading, from flawless to imperfect, cut grading, from excellent to poor and carat weight with comprehensive explanations and diamond grading charts.

The universal method of diamond grading was first introduced by the Gemmological Institute of America in the 1940s. Buying a diamond that is certified from a respected laboratory means that you can make the best-informed decision for your diamond engagement ring, wedding ring or diamond jewellery. The British Diamond Company is proud to supply diamonds with GIA, IGI, and HRD certificates.


Most diamonds are graded for their lack of colour, on a scale from D to Z, or colourless to tinted.

Each colour grade represents a range of colour, not a specific shade. The spectrum from colourless to tinted is therefore split into selected ranges that are called grades. These ranges are apparent to experienced diamond graders, based on the perceived colour in the body of the stone.

Colour grades are determined by the appearance of the diamond, firstly face down (with the culet pointing up) and secondly face up (the appearance of the diamond with the largest facet on show).

Colour Grade

Appearance of the Diamond


Face up colourless

Face down colourless


Face up colourless

Face down colourless


Face up colourless

Face down colourless


Face up colourless

Face down colourless


Face up colourless

Face down slightly tinted



Face up colourless

Face down slightly tinted



Face up slightly tinted

Face down obviously tinted



Face up obviously tinted

Face down obviously tinted


Face up definite colour


Diamond experts grade colour using a light source that excludes ultraviolet light. The diamond is assessed for colour side on or face down in the first instance. This is because the brilliance of diamond can adjust the way that colour is perceived when viewed face up.

Accurate diamond colour grading takes years of experience to master. There are subtle shades that are extremely difficult to see to the untrained eye. A good way to gauge is using the colour scale above. Face up is the view of the stone that most people will see when the diamond is set into jewellery. Diamonds classed from D to I grades appear colourless face-up, so if you are after a whiter stone then aim for these colour grades or above. However, if you are after a warmer hue for your diamond, then opt for a stone that is slightly tinted face up.


The quality of the cut of a diamond affects how much fire and brilliance it can give, and the balance between the two optical effects. Regardless of the shape of the stone, a poor cut results in a dull, lifeless diamond. Therefore, it is important to bear in mind the cut grading of any diamond you consider.

Cut is categorized by three factors: proportions, symmetry and finish.

Modern cuts of diamonds have a set of ‘ideal’ proportions or angles between facets that maximizes the brilliance of the stone. The angles of the crown, pavilion, and the size of the table facet are highly significant to diamond graders when considering the proportion of a diamond’s cut.

A symmetrical stone is also important. If the table and culet are off centre, if the stone is off-shape, if the girdle is wavy, or if the facet edges do not align, this results in a poor appearance and a loss of that ‘wow’ factor diamonds are known for.

The quality of a diamond’s polish is affected by the presence of polishing lines, burn marks. Polish is rated from excellent to poor, depending upon the presence of imperfections and how easy they are to see under 10x magnification.  


The clarity grading of a diamond refers to its internal and external imperfections, ranging from Flawless to Imperfect.

When diamond crystals form, most enclose natural features within the structure that are classed by the clarity grading system as imperfections. These are called inclusions in the diamond trade and can range from tiny pinpoint features to crystals, to fractures within the diamond.

External imperfections are known as blemishes and these can include polishing lines, additional facets, scratches and burn marks. A diamond grading report often shows a plotted diagram of the stone’s characteristics, with explanations of each inclusion or blemish noted.

The clarity grading scale takes into account the number of inclusions, as well as their visual impact. Factors such as the inclusions location, type and position can affect the clarity grading. For example, a diamond with several crystal inclusions underneath the table facet will be awarded a lower clarity grading than a diamond with a couple of feather inclusions underneath the crown facets.

Diamond experts reach the clarity grade by an examination of the stone face-up under 10x magnification.

Clarity Grading

Appearance of Diamond




Internally Flawless


No inclusions or blemishes under 10x magnification.


No inclusions under 10x magnification, and insignificant blemishes.

Very Very Slightly Included








Tiny inclusions are difficult for a diamond grader to see under 10x magnification.


Inclusions are extremely difficult to see.


Inclusions are very difficult to see.

Very Slightly Included






Minor inclusions under 10x magnification.


Inclusions that are difficult to see


Inclusions are somewhat difficult to see.

Slightly Included






Inclusions are noticeable under 10x magnification.


Inclusions are easy to see.


Inclusions are very easy to see and may be seen with the unaided eye.









Obvious inclusions under 10x magnification and can be seen easily with the unaided eye.


Obvious inclusions are visible without magnification. There may also be surface reaching fractures that affect the durability of the stone.




The carat weight of the diamond is stated in a diamond grading report. Diamonds are assessed and weighed loose from their settings so that the most accurate dimensions can be provided.

All other four Cs being equal, the greater the carat weight the more valuable the diamond. However, larger stones with exceptional colour, clarity and cut are rare, and so it is often preferable to opt for a smaller carat weight in order to keep the most desirable cut, colour and clarity grades.

For any further information on diamond grading, the 4Cs or selecting the perfect diamond for you, contact our team of diamond specialists today by calling 01335 453 453 or email us at sales@britishdiamondcompany.com.