The most well-known and misunderstood characteristic of the 4Cs is Carat Weight. It actually refers to the diamond’s weight, not its size.
A diamond’s cut impacts how large the Carat Weight will appear. Smaller carat weight diamonds will appear larger with higher cut grades.
To maximise your budget, consider buying a diamond that is slightly below your ideal carat weight. For example, instead of a 3.0 carat diamond consider buying a 2.9 carat weight.
Clarity refers to the tiny, natural imperfections that that are present in all but the rarest diamonds. The less inclusions, the better the clarity. Gemologists refer to these imperfections by a variety of technical names, including blemishes and inclusions. Because these imperfections tend to be microscopic, they do not generally affect a diamond’s beauty in any discernible way.
Colour manifests itself in a diamond as a pale yellow. This is why a diamond’s colour grade is based on its lack of colour. Blue Nile offers only Colourless (grades D-F) to Near-Colourless (grades G-H) diamonds to assure that any natural colour present is typically undetectable to the unaided eye.
A diamond’s cut grade is an objective measure of a diamond’s light performance, or, what we generally think of as sparkle. When a diamond is cut with the proper proportions, light is returned out of the top of the diamond. If it is cut too shallow, light leaks out of the bottom; too deep and it escapes out of the side.