Natural diamonds are formed from pure carbon deep within the Earth's mantle, approximately 100 miles below the surface. The process takes millions — sometimes billions — of years, requiring precise combinations of pressure and heat to transform carbon into diamond. Carried to the surface through flows of molten lava, each diamond is then mined and worked into the precious stones we know today.

Every diamond is unique, and its individual characteristics determine its value. These are known as the Four C's. Diamonds that combine the most exceptional qualities across all four are the rarest and the most valuable.

Cut

Cut is the only one of the Four C's directly influenced by human skill — the other three are entirely dictated by nature. A well-executed round brilliant cut releases a diamond's brilliance, fire and sparkle through the arrangement and proportions of its 57 or 58 facets (the tiny planes that create the angles which reflect light). When cut to the right proportions, light travels from facet to facet and disperses beautifully through the top of the stone. A diamond cut too deep or too shallow loses light through the sides or base, reducing its visual impact.

The shape of a diamond is a matter of personal taste. The round brilliant cut is the most popular, but Pear, Princess, Heart, Oval, Emerald, Marquise, Asscher and Radiant cuts are all widely chosen.

Old cut and mine cut diamonds — the types commonly found in Art Deco and vintage jewellery — are earlier forms of brilliant cut. Each was hand-cut without machine precision, making every stone individual. Key characteristics include an open culet (the small flat surface at the base where facets meet) and a relatively small table. These charming quirks are part of what makes antique diamonds so appealing.

Colour

Although most diamonds appear white, many carry subtle hints of colour barely visible to the naked eye. The closer a diamond is to truly colourless, the rarer and more valuable it becomes. Diamonds with a strong, pure natural colour are exceptionally rare and are known as "Fancies" — these include Pink, Blue, Yellow, Green, Cognac and Orange diamonds.

Clarity

A diamond's clarity refers to the degree to which it is free from naturally occurring inclusions — sometimes called "Nature's Fingerprints." The number, type, colour, size and position of these internal characteristics all affect value. Many inclusions are completely invisible to the naked eye, only becoming apparent under 10x magnification. The fewer the inclusions, the rarer the stone.

Carat Weight

Carat refers to a diamond's weight, and therefore its size. One carat is divided into 100 points, so a diamond weighing 50 points is half a carat. While size is the most immediately apparent factor in value, two diamonds of identical carat weight can carry very different price tags depending on their cut, clarity and colour.

The term "carat" originates from the carob seed, which gem merchants once used to weigh gemstones because of their remarkably consistent weight. Today, one carat equals 0.2 grams (200 milligrams) — roughly the weight of a paperclip — and is a uniform measurement used worldwide.

Gemmologists also use a point system: 50 points = 0.5 carat, 100 points = 1 carat, 500 points = 5 carats, and so on.