Diamonds are graded alphabetically from 'D' (the perfect, colourless diamond) down to 'Z'. As the colours get further into the alphabet they get more & more yellowy/brown. Many web sites tell you about the colour grading scale but what does it mean in reality? The question that experts rarely answer is 'When does a diamond start to look yellow?'. This is a slightly subjective question, but to most people the answer is that at around the colour 'J'. With a 'J' colour diamond a yellow tint is visible to most people (all be it quite a subtle one). This is very important. Many people research diamonds on the internet, find out that 'D' is the perfect colour & then think that only this or maybe an 'E' will do. This is fine if you have a substantial budget but if not you could be sacrificing a lot of the diamonds carat weight & size by choosing such a high colour grade. We would never recommend going for a very low colour just to get a 'huge rock' but on the other hand it's worth remembering that even an 'H' colour is a very white diamond.
The clarity grading of diamonds ranges from 'IF' (the perfect, internally flawless diamond) down to 'I3' (a stone with many inclusions that are visible even to the naked eye). Inclusions in diamonds can take the form of white 'feathers' that look like little cracks or can be black marks that look like grains of pepper encased in the diamond. The clarity scale is based on how noticeable the inclusions in the diamond are & not how many inclusions. 'VVS1' & 'VVS2' clarity diamonds have inclusions that are so small they can be easily missed even when looking through a jeweller's loupe (a 10 times magnifier). 'VS1' & 'VS2' clarity are still very hard to spot through a loupe whilst 'SI1' & 'SI2' inclusions can be easily found when using a loupe.
In gold carat refers to the purity of the metal but in diamonds carat is simply a weight measurement. 1 carat = 0.2gms. The word 'carat' derives from 'carob' seeds. These seeds were used as a weight measurement at markets. Customers often took their own seeds to market to avoid dishonest traders who had 2 sets of carob seeds, one for buying & one set for selling! As the carat is such a tiny weight measurement most people have trouble imagining what a 1/4 ct or a 1/2 ct diamond would look like. It is for this reason that we have this chart which converts carat weights to millimeter sizes.