The 4C’s have long been the industry standard for determining the value of a diamond.  But the characteristic of carat, colour, clarity and cut are far from equal when it comes to valuation. 

The first three C’s are fairly straight forward, referring to carat weight, colour and purity, indicating the size of inclusions in a diamond.  However, cut is a more nuanced characteristic, referring to the quality of proportions, symmetry and polish of a diamond.  It ultimately has three primary effects on appearance.  Cut impacts brilliance, the brightness which light reflects from the surface and inside the polished diamond. These factors are all to be considered when you’re browsing through diamonds for sale.
1. Carat weight
This is the standard mass unit for diamonds and other gemstones. The word "carat" comes from the old Greek word for the seed of a carob tree, "kerátion'. It is important to note there is a difference between Carat, which denotes the weight of diamonds and gemstones, and gold Karat – the purity of gold alloys.
The purest white diamonds are colourless with no hue and, consequently, have a higher value. However, diamonds can range in colour from white to yellow, brown and fancy colours. A standard diamond's colour is measured on a scale identifying the degree of colourlessness by comparing a stone under controlled lighting and precise viewing conditions to masterstones.
The clarity grade assesses a diamond for the presence and severity of flaws. No diamond is 100% perfect. With enough magnification you can find a flaw in the cleanest stone. Most flaws are naturally created when the diamond formed in the subterranean pressure of the Lithosphere. Other flaws can originate while cutting and polishing the stone.
4. Cut
Cut identifies how closely the diamond has been cut and polished to ideal proportions. A diamond's cut is not only about its shape, but how effectively the stone can return light back to the viewer's eye. A well-cut diamond will be seen as brilliant and sparkling. A poorly cut diamond may have the highest colour and perfect clarity yet it will look lifeless.


 It affects fire, the dispersion of light into flashes of colour and it gives a diamond its scintillation, the sparkle it gives off when moved, but cut can also add a lot more value and is an important factor contributing to the value of a diamond.

Given that round diamonds have become fairly standardised, large and more exclusive fancy shapes are more difficult to replicate or replace.