Acting as a prism, a diamond can divide light into a spectrum of colours and reflect this light as colourful flashes called fire. Just as when looking through coloured glass, colour in a diamond will act as a filter, and will diminish the spectrum of colour emitted. The less colour in a diamond, the more colourful the fire, and the better the colour grade. 

A Note About Flourescence

Some people seek diamonds that produce this unique effect, while others avoid it. The visible effects of fluorescence grades of faint, inert, negligible, and medium, can only be detected by a trained gemologist with specific UV light. A fluorescence grade of strong or very strong can make a diamond with a near-colourless grade look even whiter. In some very rare instances a diamond with very strong fluorescence can give the diamond a slight hazy or oily appearance. Diamonds with a strong or very strong fluorescence are a better value for the end customer because the market prices them slightly lower than diamonds with faint or negligible fluorescence.

What Colour Grade Is Best?

• For the purist, look for a colourless diamond with a grade of  D - F.
• For an excellent value in a diamond with no noticeable colour to the unaided eye, look for a near-colourless grade of  G - I.