If a diamond is the hardest known substance , what is used to cut diamonds?

The extraordinary hardness of diamonds, rated a perfect 10 on the Mohs scale, means that only another material of equal or greater hardness can effectively cut or scratch them. This makes diamonds the ideal, and often only, tool for shaping other diamonds. The Mohs scale, developed by German mineralogist Friedrich Mohs in 1812, is an ordinal scale that ranks minerals based on their ability to scratch one another, with talc at 1 and diamond at 10. While corundum (sapphires and rubies) ranks at a 9, a diamond is actually about four times harder than corundum, illustrating the non-linear nature of the scale and the diamond's unparalleled resistance to scratching.

The process of transforming a rough diamond into a sparkling gem involves several intricate steps, where diamond-tipped tools are crucial. Historically, diamond cutting practices can be traced back to the 6th century in India and the 14th century in Europe, with early techniques involving polishing natural crystal faces. Modern diamond cutting, however, utilizes specialized equipment with diamond-bladed edges or discs coated with diamond dust for sawing, cleaving, and bruting. Cleaving involves splitting a rough diamond along its natural planes of weakness, while sawing cuts through it, sometimes with the assistance of lasers. Bruting, also known as girdling, involves shaping the diamond into a round form by rubbing two diamonds against each other.

The directional hardness of a diamond is also a key factor. A diamond's hardness varies depending on the crystallographic direction. This property allows cutters to orient one diamond so that its harder grain can effectively cut another diamond's softer grain. This meticulous process, whether performed by traditional methods or with modern laser technology, ensures that the rough stone is optimally shaped to maximize its brilliance and fire, ultimately revealing the stunning beauty hidden within.