Diamond grinding

In the 17th century the French explorer Jean-Baptiste Tavernier brought large diamonds from India and described diamond mining there.

Until the 18th century, diamonds were only mined in India. This is where the most famous diamonds in history come from. In 1714 diamonds were discovered in Brazil. Erasmus Jacobs found the first diamond in South Africa near the Orange River in 1866: the ‘Eureka’. Shortly afterwards, diamonds were also found in Kimberley. In 1888 Cecil Rhodes founded the company De Beers to control the diamond trade.

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In the 20th century, important diamond deposits were discovered in Siberia, Canada and Australia, and it became possible to manufacture diamonds synthetically.

There are many legends associated with diamonds; often magical or protective powers are attributed to them. Diamonds were the symbol of wealth and they are part of almost all crown jewels, treasure chambers and museum collections. The diamond is one of the “nine gems” in the Thai Order of the Nine Gemstones.

The Cullinan is the largest uncut diamond found on earth so far: 3106 carats (621.2 grams). The Cullinan was cleaved and cut and the largest piece, the Cullinan 1 (530.20 carats) was the largest cut diamond for about a century after it was cut. The largest cut diamond since 1988, however, is the Golden Jubilee (545.67 carats), which was cut by Gabriel (Gabi) Tolkowsky on behalf of De Beers and has been in the possession of the Thai king Bhumibol since 1997, who received it on the occasion of his 50th coronation jubilee.

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.

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.

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

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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:

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 differences in symmetry?

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