The four worldwide criteria for valuing a diamond are called the four Cs. But they do not carry equal weight, and if the budget is finite, the order of importance is what decides the outcome.
Cut — the one that matters most
Cut is the only criterion that is human work rather than nature's. The angles and proportions of the cut decide how much light turns inside the stone and comes back out. A diamond of middling colour and clarity but excellent cut is more brilliant than a flawless one cut badly. If there is one place not to economise, this is it.
Colour
From D, entirely colourless, to Z, visibly yellow. The difference between D and F is all but invisible to the naked eye, while the difference in price is not. In a yellow gold setting, even H and I read as white.
Clarity
How many inclusions there are, and where. From FL, flawless, down to I. The practical point: from VS2 upwards, inclusions cannot be seen with the naked eye. The trade calls that range eye-clean.
Carat
Weight, not size. Price does not rise linearly with weight: a two-carat diamond is far more expensive than two one-carat diamonds, because large stones are rarer. Price also jumps at the round weights — a 0.95 carat stone is considerably cheaper than a 1.00, and the eye cannot tell them apart.
In order of what the eye notices: cut, then size, then colour, and clarity last.
The stone report
For any stone over a carat, ask for a report from an independent laboratory. For high jewellery, Goharbin supplies the stone report alongside the certificate of authenticity.
