Diamond Grading
Colour
White, completely colourless is considered the best for non-fancy diamonds. Colour is determined using a master set of stones with colour grades established using internationally recognized standards. It is graded using letters from D to Z, in alphabetical order, with D being absolutely colourless and Z having a very obvious shade of yellow or brown that is not intense enough to call it fancy. Usually the most popular stones are D, E, F, G, H, I, J, with K-Z being noticeably yellow or brown and so less desireable (they are also substantially cheaper).
Interestingly, the difference between diamonds in the range D-J will not be obvious under normal conditions: only upon very close inspection with proper lighting and possibly even some training that you would be able to tell them apart. In this range the cut of the stone will often affect the appearance of the colour more than the official colour grade.
Another important factor is that the tint becomes more obvious as the diamond's size goes up. A 0.5 carat J stone can look as yellow as a 1.5 carat F one under normal conditions, such as when worn together in a piece of jewellery. This is because the colour becomes more intense as the distance the light travels inside the diamond increases.
There is a very easy way to fake a colour grade in a set jewellery at the point of sale: a tiny dot is placed at the culet of the white diamond with a blue pen. This will make a diamond appear 1 or 2 color grades better. The problem of course, is that this dot will wear off very quickly as you wash your jewellery and the diamond will look more yellow. This trick is very difficult to spot if buying jewellery in person at a retail store with lots of bright lights in the interior. A dishonest jeweller can this way persuade you that a certain diamond is of higher quality than it is, and you will end up paying much more than you should have. Almost any diamond will look wonderful under bright display lighting, but the difference becomes more apparent as you bring it home and look at it in regular light. For this reason, make sure the diamonds you buy, loose or set, are accompanied by a grading certificate from an accredited laboratory, not from a store related one. Such fraud is more common in the underdeveloped tourist destinations where chances of the buyer and seller meeting again are very small. Most of the jewellers working legally in the developed regions like North America or Europe would not do this, since the long term benefits of having a satisfied customer make repeat purchases far outweight the immediate gratification of extra profits.
