Understanding the 4Cs

The colour evaluation of most gem-quality diamonds is based on the absence of colour. GIA’s D-to-Z Colour Grading System measures the degree of colourlessness by comparing a diamond, under controlled lighting and precise viewing conditions, to masterstones of established colour value. Many distinctions are subtle to the untrained eye, yet they can have a significant impact on quality and price.

Internal inclusions and external blemishes are part of a diamond’s natural formation and history. Clarity is assessed according to the size, location, visibility, and number of these characteristics, as well as their effect on the stone’s overall appearance. While very few diamonds are perfectly pure, greater clarity is generally associated with greater rarity and value.

Cut plays a defining role in a diamond’s beauty, influencing how it returns light to the eye. Of all the 4Cs, it is often the most technically complex to evaluate. For standard round brilliant diamonds in the D-to-Z colour range, the GIA Cut Grading System considers seven components: brightness, fire, scintillation, weight ratio, durability, polish, and symmetry.

Carat weight refers to a diamond’s weight, with one metric carat equal to 200 milligrams. All else being equal, larger diamonds are rarer and often more valuable. However, two diamonds of the same carat weight can differ greatly in beauty and price depending on their cut, colour, and clarity.