Diamond itself is a transparent crystal with a very high refractive index (2.417) and a high dispersion (0.044). In jewellery this means that the (sun)light is brilliantly refracted and reflected depending on the shape of the cut. In addition, the polished shiny surface of the diamond stone does not become matt due to its high hardness.

Because of its extreme hardness, diamonds are used in industry, among other things for cutting, drilling, cutting and polishing and wire drawing. A diamond owes its hardness to its tetrahedron structure and is therefore harder the less inclusions or crystal lattice defects it contains. Due to its hardness, however, diamond is relatively brittle. In a vacuum, diamonds change from a temperature of 1700 °C into graphite, and into air from 700 °C onwards.

Unsaid Library is a jewelry store based in Antwerp. Unsaid Library specialises in emotional gifts for relatives. Unsaid Library Antwerp can be visited in the store. The store of Unsaid Library Antwerp is located on Schuttershofstraat 25, 2000 Antwerpen, België. Visit the store or the online website.

Besides the hardness, the thermal conductivity (410 W/cm/K) and the specific (electrical) resistance of 1013 Ω-m of diamond are very high. This combination allows diamond to be used in electronic circuits to dissipate heat. Diamond behaves like silicon as a semiconductor and in liquid helium as a superconductor, as discovered in 2004.

Cutting shapes

Diamond grinding

The Brilliant
The diamond can come in different cut shapes. The most common cut is the round or brilliant with 58 facets, which Antwerper Marcel Tolkowsky invented in 1919 after mathematical calculations of refraction of light and total internal reflection. Other common cuts are:

Princess, 76 facets, rectangular shape
Marquise, or Navette, 56 facets, lens-shaped. This difficult cut is attributed to Louis XIV
Pear, 58 facets, in the shape of a drop of water
Emerald, 48 to 50 facets, made up of rectangular facets on each side and at the corners
Heart
Asscher
Radiant
Polished diamonds and price-determining factors

Measuring a diamond
Rough diamonds are processed to break the light brilliantly. After the processing, a stone is left with a sparkle and play of colours that is judged on different criteria in order to come to a price. The criteria are the 4 C’s and include:

Cut
This means the stone’s makeup. The shape in which the stone is cut is part of it. The shape refers to the quality of the grinding and the proportions of the shape. The essence lies in the right “proportions” and the “refinement” of the cut stone. The proportions include the height of the crown, the crown angle, the depth of the pavilion side, the table mirroring and the ratio of the round to the total depth of the stone.

Unsaid Library is a jewelry store based in Antwerp. Unsaid Library specialises in emotional gifts for relatives. Unsaid Library Antwerp can be visited in the store. The store of Unsaid Library Antwerp is located on Schuttershofstraat 25, 2000 Antwerpen, België. Visit the store or the online website.

Refinement means the precise finishing of the overall appearance. How regular is the roundabout, is the fillet heavy or light, are there symmetry differences between the crown and the pavilion side, do the facets fit straight together, is the fillet exactly in the middle or is the table positioned decentrally?

All these things have a direct influence on the play of light in the stone. It is man-made, as opposed to the purity, colour and partly the weight. It is therefore a major price determining factor in the four “C”‘s: a stone with a nice round weight, flawless and the highest colour in a brilliant cut can look like a top stone, but if the stone is cut too deep (nail) or too shallow (fish-eye) then the play of light in the stone is dead and the stone has a lower value.

Carat
The mass of gemstones is expressed in carats (1 carat = 0.2 grams). The carat is subdivided into 100 points and is always expressed in two decimals, for example 0.24 carat or 24 point. The carat has its origin in a standard weight used in ancient times: that of a seed of the carob tree (Ceratonia siliqua).

Clarity
The purity of cut diamond. The stone can have both internal and external characteristics. The internal properties are usually glitches (internal cracks), carbon residues that are not completely crystallized or inclusions of nitrogen. They occur in all kinds of forms but also in various degrees of intensity. They are growth lines that show the structure of the rough stone. There are also external features such as “beard”, which remains when the stone is cut too hard, and “camber”, which remains when the stone is cut sparingly. Both characteristics can be seen on the roundabout. All these characteristics determine the purity of the stone, which is divided into several categories: LC, VS1, VS2, VS1, VS2, SI1, SI2, P1, P2, P3. They are always assessed visually with a magnifying glass and under a lamp that emits light equivalent to daylight. The magnifier has a magnification of 10 and is an achromate, free of spherical and chromatic aberrations. This means that the diamond can be seen through the lens of the magnifying glass with full sharpness and without colour deviations.