How to Cut a 404 Carat Diamond

404 ct diamond rough
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Earlier this year, a 404-carat rough diamond worth about $14 million was found in the African country of Angola. The diamond, which was 7 centimeters long, and the largest ever found in the region, has since been split into hundreds of brilliant diamonds. It takes hours of cutting and polishing to turn a rough diamond into something sparkling and beautiful, but have you ever wondered how exactly a diamond is cut? Read on to discover what it takes to turn a rough stone into a precious cut, jewelry-worthy diamond.

The Actual Diamond Cutting Process

The process of how diamonds are cut and polished can be broken down into five steps: planning, cleaving (or sawing), bruting, polishing and inspecting. The goal is to cut a rough diamond in a way that minimizes waste and removes inclusions while creating as many precious diamonds as humanly possible. Not just anyone can cut a diamond – due to the extreme difficulty, diamond cutting requires very specialized knowledge, tools, equipment, techniques and years of practice. A highly trained diamond cutter inspects the diamond rough from all angles to determine which areas would create the best diamonds with the least possible waste. This intricate inspection can take weeks for even the most skilled diamond cutter: each piece of diamond rough is unique and can be cut to form any diamond shape, but a diamond cutter can’t start until they have a plan.

For example, a piece of rough that’s shaped like a ball might yield two very nice round cut diamonds. The cutter would cut the rough at an angle to make two rounds out of each half, like so:

Ideal cut rough diamond

On the other hand, a piece of rough that is flat-shaped is usually better for a step cut diamond such as an emerald or asscher, since cutting a round shaped diamond out of a flat piece of rough would waste a lot of the valuable pieces of the stone.

If the rough diamond is irregularly shaped, the cutter might cut one side as a round stone and the other as a modified brilliant fancy shape like princess or radiant. The diamond rough might also have natural inclusions that the cutter wants to dispose of while cutting the rough. Whatever the type of rough, it takes an expert to determine how to cut it in order to maximize its value. In most diamond cutting labs, this is a specialized person whose only job is to determine where and how to cut the rough. Sounds like they’re always under a lot of pressure! (that was a diamond joke, get it?)

Diamond cutting wheel

2 Ways to Cut a Diamond: Sawing vs. Cleaving

Sawing is just what you would think: A trained diamond cutter uses a diamond saw (which itself has thousands of small diamonds on the blade) to cut the rough diamond in a sawing motion. Today, some cutters also use lasers instead of a manual saw to cut the rough. This is more common with smaller pieces of diamond rough that are under 1 carat in weight.

Alternately, when using the cleaving process, the diamond cutter uses a rod and hammer to strike the rough diamond at a precise point, splitting it into two pieces. In this case, the diamond cutter creates a mold that holds the rough and a small indent is made where the diamond is to be struck. In some ways it’s similar to cutting a piece of wood with an ax — however, it needs to be done with one strike and without any mistakes to yield two perfect pieces.

Diamond rough planning and marking

Shine Bright Like a Diamond: Bruting and Polishing

After the initial cut of the rough is done, the diamond cutter moves on to a process called bruting, in which two diamonds are rubbed together on a specialized machine to chip away at the rough. This begins to form the shape of the diamond. The bruting process must be done slowly over several days, because moving too quickly could shatter one of the diamonds as they grind against each other.

Once bruting is complete and the diamond has its basic shape, the diamond is passed on to another highly skilled craftsman for polishing on a wheel. A diamond polishing wheel contains a heavy piece of rotating diamond “sandpaper.” The diamond polisher moves the diamond against the wheel to create facets or step cuts, depending on the desired shape. It takes years to master the technique of faceting a stone without destroying it on the wheel.

Woman analyzes Pear shaped diamond

Once the final polishing is done the diamond is inspected, usually by the head diamond cutter. Once it is approved the new diamond is sent out to either the Gemological Institute of America (GIA) or the American Gemological Society (AGS) laboratory to be graded. After it is returned from the lab, the diamond is priced and ready to become a treasure to a lucky person.

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To learn more, check out our Advanced Diamond Education, where we teach you everything you need to know about the anatomy of a diamond and how they are graded by the GIA and AGS.