How are diamonds cut?
How Do You Cut Hardest Material On Earth?
In most cases, a diamond will be cut with a saw blade. Since diamonds are the hardest material known only diamonds can cut diamonds. So the diamond is securely mounted and held against a thin alloy blade covered with diamond dust and linseed oil. As the blade turns, it carries small particles of new diamond dust which sticks to the oil and continues the process until the entire diamond is split in two. This can take several days for a diamond over 1 carat or more.
After a diamond is cut in the height and width desired, it is crudely shaped into a round or other shape by rubbing it against another diamond on a high-speed lathe specially designed for this purpose. Then the long and precise process begins to create the many facets that you have seen on diamonds in stores. Each facet is created by grinding the diamond on a horizontal blade as it spins. First, the large facet at the top is ground until level and smooth. Then the major facets are created on the bottom, followed by the large facets on top.