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Diamond is not only the hardest substance in nature, but also one of the most cherished gemstones of human beings. The beauty and value of a diamond depends largely on its cutting craftsmanship. A Seiko cut diamond can emit dazzling brilliance and fire, while a shoddy diamond may appear dim. So how are diamonds cut? What are the scientific principles and technical secrets behind this?

We all know that to cut an object, it is necessary to exert force on it with something harder than it. For example, we can cut wood with a steel knife, but not with wood. So, to cut a hard substance like a diamond, you need to exert force on it with something harder than it. According to the Morse hardness standard, the hardness of diamond is 10, which is the hardest substance known in nature.

The reason why a diamond is so hard is due to the special properties of its crystal structure and chemical composition. First of all, the crystal structure of diamond is so close that each carbon atom forms a covalent bond with four adjacent carbon atoms, forming a cell structure similar to a triangular cone. This crystal structure gives diamonds a very high density and hardness.

Secondly, the chemical composition of diamond is also an important factor in its high hardness. Diamonds are made of pure carbon, which is a very stable element with a strong covalent bond structure, which makes it very difficult for diamonds to be eroded and destroyed by other elements or chemicals.

In addition, the crystallization process of diamond also affects its hardness. Diamonds are formed in an environment of very high temperature and high pressure, which enables carbon atoms to combine closely and form a perfect crystal structure. This perfect crystal structure further improves the hardness of the diamond.

So, is there anything harder than diamonds? The answer is yes. Among the synthetic materials, there are some superhard materials, such as carbon nitride, graphene, carbyne and so on, which are harder than diamonds. However, the preparation and application of these materials are very expensive, so they are not common. Therefore, although there are synthetic substances that are harder than diamonds, they are not suitable for cutting diamonds. At present, the most practical and economical way is to cut a diamond with another diamond.

First of all, we need to know that diamonds are not as hard in all directions. The crystal structure of a diamond determines that it has certain directions, called cleavage planes, along which the bond between atoms is weaker, so it is easier to cut open. This is the first method of diamond cutting: split.

Split is to use the cleavage surface of a diamond, use another diamond or a special knife to make a groove in the diamond surface, and then hit it with a hammer to make the diamond break along the groove. This method can quickly divide large pieces of diamond into small pieces, but it also carries great risks. If the percussion force or angle is not appropriate, or the cleavage surface is not clear, the diamond may break into useless fragments. Therefore, this method requires cutters to have high skills and experience. The advantage of split cutting is that it can retain more original weight, but the disadvantage is that the shape and size of the cutting can not be accurately controlled. If you want to cut the diamond into a more regular and symmetrical shape, you need to use a second method: sawing.

Sawing is the use of a substance harder than or equivalent to a diamond to rub against the diamond surface and gradually wear off the excess part. The most commonly used sawing tools are metal saw blades or wires coated with diamond powder. This method can saw the diamond into the desired shape according to the design pattern, but it also has a lot of wear and tear. Generally speaking, sawing loses more than half of its original weight. The advantage of sawing is that the shape and size of the cutting can be accurately controlled, but the disadvantage is that the loss is large and the speed is slow. In order to improve efficiency and reduce loss, modern cutting technology introduces a third method: laser cutting.

Laser cutting uses a laser beam with high energy density to heat and evaporate on the diamond surface to remove the excess. This method can complete the cutting in a very short time, and it can be cut in any direction without the restriction of cleavage surface. However, laser cutting also has some disadvantages. First, laser cutting leaves a black or gray carbide layer on the diamond surface, which requires extra polishing to remove. Second, laser cutting will produce very high temperature and pressure, which may lead to cracks or bursts inside the diamond. Therefore, laser cutting is usually used in combination with other methods to achieve the best cutting effect.

After cutting, the diamond still needs to be polished before it can show its final brilliance. Polishing is the use of harder than or equivalent to diamonds, friction on the diamond surface, gradually smooth the surface of the uneven and scratches, so that the diamond surface to achieve a mirror-like smoothness. Polishing powder is generally composed of iron oxide, chromium oxide, silicon carbide or natural diamond powder.

This article comes from the official account of Wechat: Vientiane experience (ID:UR4351), author: Eugene Wang

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