The 4Cs

No two diamonds are alike. Each one is unique.

This is why over the years a universal standard for identifying diamonds has been set. The quality and value of a diamond is defined according to the 4Cs: carat, colour, clarity and cut. At HRD Antwerp, we are experts in analysing these characteristics. Our diamond grading reports cover all 4Cs of diamond certification for loose diamonds, ensuring consumers know exactly what diamond they are buying. 

Learn everything you need to know about the 4Cs in our interactive showcase

Natural diamonds

Natural diamonds are created by geological processes. They are formed at extremely high temperature and pressure at depths of hundreds of kilometres in the earth's mantle. Most diamonds found in nature are over 1 billion years old and extremely rare. In a typical mine, 100 tons of rock needs to be processed in order to find a diamond larger than 1 carat. It takes time and effort to enjoy these pure wonders of nature we cherish so dearly.


Types of diamonds

A diamond with a perfect crystal lattice made entirely of carbon would be completely colourless. In reality, however, all diamond crystals contain atomic impurities and structural imperfections. We call these 'colour centres' because they are responsible for the colour of a diamond. The most common atomic impurity in a diamond is nitrogen. Based on the presence of this atom in the diamond lattice, one can classify diamonds into two main groups. Type I diamonds contain a higher level of nitrogen, while type II diamonds contain practically no nitrogen.

Lab grown diamonds

A laboratory grown diamond is man-made but features the same optical and physical properties as a natural diamond, including its chemical composition, refractive index and 4 Cs. The only difference is its point of origin: one is grown above ground, while the other is extracted from the ground. Laboratory grown diamonds can be produced by two methods. One is HPHT, under high pressure and high temperature; the other is CVD, chemical vapour deposition.

HRD Antwerp provides grading services for disclosed synthetic diamonds.

Treated diamonds

General Electric (GE) developed the high pressure (HP) – high temperature (HT) colour treatment in the mid-nineties with the goal of changing the colour of 'lower quality' (read: light brown) diamonds. During this treatment, the stone is heated to temperatures of over 2100°C. To prevent the diamond from being transformed into graphite, this process takes place at a very high, stabilising pressure. The brown colour in some types of diamonds (including type IIa) is associated with the presence of plastic deformation or defects in the crystal lattice. HPHT treatment changes these defects in the crystal lattice. Consequently the cause of the colour disappears.

The whole process often takes only a few minutes, but the diamond needs to be cut afterwards to remove the mat, corroded surface and regain its sparkle. The final result of this treatment greatly depends on the initial properties of the diamond and its type. Today, a brown, grey or light yellow diamond can be 'transformed' into a diamond ranging from intense yellow to greenish-yellow, pink, blue or colourless.

Fancy coloured diamonds

Diamonds occur in all sorts of colours. If a diamond displays a colour other than light yellow or light brown in the face-up position, it falls into the category 'fancy coloured diamonds'. Many of these fancy diamonds are quite rare, especially the red, green, and blue ones.

Grading fancy coloured diamonds is a complex process, seeing they are mainly valued for the intensity and distribution of their colour. Of course, the diamond cut, diamond clarity and carat also need to be taken into account. Our expert gemologists meticulously analyse each diamond to deliver an accurate Natural Diamond Colour Grading Report.