Everything about diamond grinding

Many diamonds for industrial purposes are also made synthetically. Synthetic diamonds can only be distinguished from natural diamonds in a laboratory. Researchers from the Carnegie Institution of Washington discovered in 2004 a process to synthesize within 24 hours diamonds that are more than 50% harder than natural diamonds.

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Physical properties

The crystal structure
Diamond is the hardest material in nature. There are only two (industrially manufactured) materials that are harder, namely aggregated carbon nanorods and ultra-hard fullerene. Like diamonds, these are made up of carbon atoms. Diamond itself is a transparent crystal with a very high refractive index (2.417) and a high dispersion (0.044). In jewellery, the (sun) light is therefore brilliantly broken and reflected depending on the shape of the cut. In addition, the polished polished surface of the diamond stone does not become matt due to its high hardness.

Because of its extreme hardness, diamonds are used in industry, for example for grinding, drilling, cutting and polishing and wire drawing. A diamond owes its hardness to its tetrahedron structure and is therefore harder when it contains fewer inclusions or crystal lattice defects. Diamond is relatively brittle due to its hardness. In vacuum, diamonds are transformed into graphite at a temperature of 1700°C and into air at a temperature of 700°C.

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Besides the hardness, the thermal conductivity (410 W/cm/K) and the (electrical) resistance of 1013 Ω-m of diamond are also very high. This combination makes that diamonds can 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.

Grinding moulds

Diamond Grinding

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

Oval, 56 facets
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, composed of rectangular facets on each side and at the corners

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

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Cut
This is understood to mean the creation of the stone. The shape in which the stone is cut is a part of this. The product relates to the quality of the grinding and the proportions of the grinding form. 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 reflection and the ratio of the roundness to the total depth of the stone.

Refinement is understood to mean the precise finishing of the total product. How regular is the round-distant, is the column heavy or light, are there symmetry differences between the crown and the pavilion side, do the facets fit straight together, is the column exactly in the middle or is the table decentralized?

All these things have a direct influence on the play of light in the stone. The product is human, in contrast 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 may look like a top stone, but if the stone is cut too deep (nail) or too shallow (fish eye) then the light play 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 divided into 100 points and is always expressed in two decimals, for example 0.24 carat or 24 points. 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 polished diamonds. The stone can have both internal and external characteristics. The inside usually consists of glitches (internal cracks), carbon residues that are not fully crystallised or nitrogen inclusions. They occur in all kinds of forms but also in various degrees of intensity. These are growth lines that show the structure of the raw stone. There are also external characteristics such as “beard”, which remains when the stone has been cut too hard, and “nerve”, which remains when the stone has been cut too sparingly. Both characteristics can be seen on the rim.