Diamonds are the hardest minerals on earth. As such, it is not a simple task to turn a rough diamond into a polished stone. Cutters need to weigh-up the pros and cons of each of the 4 C's and how they relate to each other. They also factor in the popularity of various styles and how easy it will be to sell the finished product.
Before any cutting is done the cutter needs to plan the cut. They do this by studying the crystal structure for inclusions and deciding which type of cut will yield the best proportions and maximum weight. Once a cutter understands the crystal direction, cutting can begin.
If a diamond needs to be separated into two pieces, the cutter can split it by sawing or cleaving. Cleaving involves making a mark in the diamond called a kerf, inserting a blade in the kerf and striking it with a hammer. This should cleanly separate the rough into two pieces. To saw a diamond the cutter must find the cubic plane. Once the cubic plan is located the diamond is lowered onto a diamond saw and separated cleanly.
After a diamond is sawed it is bruted. Bruting helps to shape the girdle outline by forcing one diamond against another. Typically bruting is automated by machines and the process take about 30 seconds per diamond.
The last stage of the cutting process is polishing. Polishers use a spinning disk called a scaife.
The first step is called blocking where the cutter will put the first 17 or 18 facets on a diamond. After this, the final facets around the girdle and crown are cut by a specialist called a brillianteer.
Modern technology has aided diamond cutters in automating many parts of the cutting process, however careful planning, consideration and human touch are all required to turn a rough diamond into a polished gem.