Diamonds are famous for their beautiful ‘white’ or colourless appearance, but almost all have at least a hint of yellow or brown. This is often imperceptible to the untrained eye, but it can make a significant difference to the price of a stone. To make things easier, diamonds are assessed using the colour grading scale created by the Gemological Institute of America (GIA).
The colour grading scale uses letters to indicate the grade, beginning at ‘D’ for stones with a complete absence of colour and continuing through the alphabet as the level of colour increases. Diamonds graded from ‘D’ to ‘F’ are regarded as colourless, those from ‘G’ to ‘J’ are near colourless. Diamonds with these grades should appear colourless, or nearly so, to the eye when viewed face-up. Stones with grades from ‘K’ downwards will have more obvious hints of colour, which increase as you move further down the scale.
Customers often ask us why the grades begin at ‘D’ rather than at ‘A’. Prior to the development of the GIA system there were a variety of different, inconsistent systems in use. Some of these used numbers while others used letters, with more broad groupings than are now used such as ‘A’, ‘B’ and ‘C’, multiple ‘A’ grades denoting the finest quality. Selecting ‘D’ as the highest grade allowed the GIA to create a completely new system and avoid confusion with existing grades. It is now the industry standard used across the world.
Diamonds are graded by comparison with a master set of stones of known colour. This takes place under very controlled conditions, ensuring for instance that the lighting is always absolutely the same, and the background the stones are being viewed against is always identical. The diamond is placed with its table facet (the large flat surface on the top of the stone) facing down, and the grader views it from the side, where the maximum colour should be seen.
When diamonds are assessed for their colour outside of laboratory conditions the grade is estimated, and is often given as a small range, such as G/H or J/K. The differences between individual grades are incredibly subtle.
We often describe diamonds as ‘facing up well’. This means that they appear ‘whiter’ or display less colour when viewed from the top (as you view a set diamond) than their grade suggests. This is due to the way the diamond interacts with light, the bright reflections of brilliance the stone produces, and the angle of viewing both minimising the amount of colour seen. Another factor can be the fluorescent properties of the stone.
Some materials emit a visible fluorescent glow under ultraviolet light. Diamonds have quite a variable response, with some not reacting at all while others have a very bright glow, commonly blue but sometimes other colours. One of the side effects of this property is that diamonds which fluoresce also appear ‘whiter’ in ordinary daylight. Fluorescence can also cause a hazy appearance, so it is not always an advantage, but a little can sometimes give a little boost to the colour. A diamond certificate should state how strong the stone’s fluorescence is, but the impact of this can only be seen by looking at the stone.
It is important to bear in mind that everyone perceives colour differently; some eyes are more sensitive than others. Some people will notice the colour in a diamond that others observe as colourless. This is one of the reasons that it is always a good idea to view a diamond in person rather than relying on a certificate. What you see is the crucial thing.
Our showroom is staffed by highly qualified and experienced jewellers, including several qualified diamond graders. We are always happy to discuss diamond grading with you and answer any questions you may have about diamonds. We have diamonds in stock in colour grades from D to L so that you can view and compare qualities enabling you to make an informed choice.