The colour of a diamond is considered one of the key factors in determining the value of the stone. A traditional diamond is considered to be a 'white' stone, although they can actually be found in many colours, such as pink and yellow.
The most desired and precious traditional 'white' diamond should be as colourless as possible. The GIA (Gemological Institute of America) defined and developed a very precise scale of colour grading, and use this to grade diamonds by comparing them to a master stone. This is done under controlled conditions such as controlled lighting and precise viewing conditions to be as exact as possible.
There are a number of other grading scales available from other grading institutions such as the IGI (International Gemological Institute) AGS (American Gemological Society) CIBJO (The World Jewellery Confederation) and HRD Antwerp – Institute of Gemmology.
The GIA colour grading scale exactly matches the one used by the IGI, which is what we at H.Samuel use to grade our diamonds. The scale runs alphabetically from D to Z+, with D being the highest, best grade possible given to diamonds that are the rarest and most desirable. This is the grade that is classed as colourless. The full scale runs as below:
Z+ diamonds indicate that this type of diamond is what we call a coloured diamond, and so should have a vivid hue of the colour in question. A yellow diamond would fall under this category, whereas white diamonds with a hint of yellow falls will fall somewhere in between the scale above. Remember, the higher up the alphabetical colour grade, the better the colour of the diamond – increasing the value.
Completely colourless diamonds are exceptionally rare. High quality commercial diamonds are most likely to fall within the G-J grading of 'near colourless.'