Natural Diamonds & the 4Cs Explained | Martin Nagel Jewellers

Diamond education

Understanding the 4Cs of diamond quality

Cut, colour, clarity and carat weight together determine a diamond’s beauty, rarity and price. Understanding them helps you choose the best diamond for your budget – and Martin will guide you through every option, natural or lab-grown, in person.

01Cut 02Colour 03Clarity 04Carat

Diamond cut grades from Excellent to Poor

Cut

Cut is perhaps the most important of the 4Cs. It doesn’t refer to a diamond’s shape, but to the quality of its workmanship – the proportions and arrangement of its facets. A well-cut diamond returns more light, giving it more brilliance, sparkle and fire. Grades range from ‘Excellent’ to ‘Poor’.

Fancy shapes such as pear, oval or heart don’t receive a GIA cut grade, because their proportions vary more widely.

Martin’s tipMost diamonds on the market have an ‘Excellent’ to ‘Very Good’ cut. A ‘Poor’ cut will look dull and lifeless – never compromise here.

Colour

Colour measures a diamond’s absence of colour. Most “white” diamonds contain traces of yellow, brown or grey – the less colour, the rarer and more valuable the stone. The scale runs from D (completely colourless) to Z (light colour); beyond Z are fancy-coloured diamonds.

Differences of one to three grades are hard to see with the naked eye – graders compare stones face-down under controlled light.

Martin’s tipD, E and F are rare and expensive. G and H offer excellent value and still face up beautifully white. Colour becomes more visible from I downwards.

Clarity

Clarity measures the size, number and position of internal ‘inclusions’ and external ‘blemishes’. Grades range from Flawless (no imperfections at 10x magnification) to Included. Diamonds down to VS2 or SI1 usually have no eye-visible inclusions and can be great value; I1 and below have inclusions that are easy to see and can affect durability.

Martin’s tipBrilliant cuts hide inclusions better than step cuts. For an emerald or Asscher cut, choose a higher clarity than you would for a round or oval.

Carat

Carat is a diamond’s weight. Generally, the higher the carat, the larger and more valuable the stone – but how big a diamond looks also depends on its proportions. A well-spread stone can look larger than a deeper one of the same weight.

Martin’s tipPrices jump at “magic sizes” like 0.50, 1.00 and 1.50ct. A 0.90–0.95ct diamond looks almost identical to a 1ct – at a noticeably lower price.

What about fluorescence?

Some diamonds glow blue under UV light. Learn when fluorescence matters – and when it can actually save you money.

Read about fluorescence →

Find your diamond

See real diamonds side by side

The best way to understand the 4Cs is to see them. Book a private consultation and Martin will show you certified GIA, IGI and EGL diamonds – natural and lab-grown – to find the perfect balance for your budget.

Book a consultation Lab-grown diamonds

Diagrams courtesy of GIA