Colour

The colour of a diamond refers to the amount of “yellowness” that the diamond has. While typically you might think of diamonds as being colourless, in fact, most have a yellow hue to them (due to nitrogen contamination). If the other 3 Cs are held equal, the more colourless the diamond, the more expensive that diamond is.

However, very intensely yellow diamonds are highly prized and can be very expensive. These are known as Fancy Yellow diamonds.

Colour is graded on sliding scales. The GIA (Gemological Institute of America) scale, ranging from D to Z, is the most common colour scale used in the UK. Some of the other gemological laboratories have a different scale for diamond colour.

Because of the gradual increase in colour up the scale, it is very difficult for the untrained eye to tell the difference between one grade and the next grade. For example, telling the difference between an “F” colour diamond and a “G” colour diamond is difficult. However, it is much easier to tell the difference between a “D” grade diamond and an “I” grade diamond. 

“D” colour diamonds are very rare and subsequently are very highly priced relative to the other colour grades.

So you now know, if you decide that you wish to buy a near colourless diamond then you pay proportionally more for a “D” grade than you do for an “E” grade.

You might be wondering how a diamond is actually assigned a colour grade. There are two primary methods:

1. Using a set of reference diamonds. These are a set of diamonds that have already been graded for colour by one of the gemmological institutes. They act as a baseline for determining the colour of other diamonds that they are compared to. Once the diamond has been graded, this grade is entered onto its laboratory certification and will not need to be graded for colour again.
2. A Colorimeter. This is a device which beams a ray of light through the top of the diamond. The beam passes through the diamond and then through various light filters. A receptor analyses the beam and measures the absorption of the colours. The analyser determines the colour of the diamond according to the degree of absorption of the other colours of light. 

Fluorescence is a factor that partially affects the colour of a diamond that you may not even hear mentioned by any jeweller you consult. Fluorescence is the glow that is produced when a diamond is exposed to ultraviolet (UV) light. It is due to the diamond containing tiny amounts of the element Boron. The most common glow colour is blue, although other colours are also possible.

There is ongoing debate about whether fluorescence actually improves or detracts from a diamonds appearance. Whatever the case, most consumers try to avoid diamonds with fluorescence and will certainly not pay a premium for a diamond with fluorescence.

Tips on Diamond Colour
When assessing a diamond’s colour there are a few rules of thumb you should follow:

• You must look through the side of the diamond to see the true colour, not the top or bottom.

• The diamond should be viewed against a plain, preferably white background (a black or dark background will make a diamond look more white than it actually is). 

• Start by “getting your eye in” by comparing diamonds with several grades of colour between them, for example, a “D” coloured diamond with a “J” coloured diamond (keep the other 3Cs constant.) The difference should be quite noticeable. Move onto comparing, say, an “E” with a “H”. These should be more difficult to tell apart. Finally, compare two stones of only one colour grade difference, such as an “F” compared with a “G”. 

• The diamond must be un-mounted, that is, not already set into a ring. If it is already mounted you will find it very difficult to get a clear view of the diamond and thus a true indication of its colour. 

Always purchase diamonds that have been graded by one of the independent gemological institutes and have an authentic laboratory certificate accompanying the diamond.

• Make sure the diamond is being viewed under lighting that simulates natural light conditions as closely as possible. Some jewellers use bright halogen lamps which give an unnaturally intense sparkle to a diamond. The diamond will then look much duller when viewed in natural light.

• A jeweller will generally “round up” the colour of a diamond in his/her favour, for example, if a diamond colour grade looks like it is somewhere between an “F” and a “G”, the jeweller will round it to “F”, as this would command a higher price. To avoid this, always make sure the diamond has a laboratory certification, from which you can then confirm a diamond’s officially graded colour.