Bruting is a process in diamond cutting that establishes the girdle outline. Once the height and width of the diamond are determined, it is then shaped along the girdle edge by grinding it against another diamond on a specially designed, high-speed lathe. This process is responsible for the creation of the round brilliant-cut. Prior to the invention of bruting, there was no efficient way to round the outline of a diamond.
Diamond Bruting Machine – Rounding 2 Diamonds by Grinding them Together as They Spin.