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How To Cut A Diamond

Have you ever wondered how you go from a piece of rough to a perfectly polished diamond?

We've come to Antwerp to have a look at the process in more detail. First off all the diamonds need to be sorted into parcels. The stones are also sorted according to the size of the stone and the shape and the clarity and the colour of the stones. These are the main criteria.

When the diamonds are being sorted for shape the diamond sorters are not looking at the stones to be either round, brilliant or princess cut but instead are looking for makeable stones or sawable stones. A makeable stone is the name given to diamonds whose shape lends itself to having one large diamond cut from it. Sawable stones on the other hand are cut in half in order to create two smaller diamonds. Once they have been sorted the parcels are handed over to the head of polishing. It's now their job to assess each rough diamond individually and create a cutting plan which details exactly the size and angle of every facet for the diamond.

Each diamond is first scanned into a computer using a machine and then using a sophisticated piece of computer software the different cutting options can be analysed. This is a crucial stage in assessing how beautiful the diamond will ultimately look. The polishing company can decide to retain a greater portion of the original carat weight of the diamond, perhaps by making the diamond slightly deeper or slightly taller. In this case the diamond will weigh more but as the position of the facets are less than optimal they won't reflect the light as well resulting in less sparkle and life in the stone.

Once a cutting option has been confirmed the diamond is then handed to the first polisher. He puts the first eight facets on the diamond, four on the pavilion and four on the crown which is on the top of the stone. During this process the diamond is secured in a special bracket which holds the diamond at an exact angle. It's lowered onto a turntable which is covered in a diamond paste that slowly polishes away material from the rough diamond.

The next stage in the process is to make the diamond round. This is done using a bruiting machine. Two diamonds are turned against each other to make the diamond round in shape. This process leaves a matt like finish on the girdle of the diamond. The girdle can be left in this form which is called a bruited girdle or a series of small facets can be polished onto the girdle, giving a faceted girdle.

Now that the diamond has its basic shape it's taken to the next polishing stage where the main pavilion and crown facets are polished on.

It's important that each facet is polished to be in line with the original cutting plan produced by the head of polishing. Once the diamond has been polished, every single facet needs to be carefully checked. First this is done using a laser scanner and then by a professional gemologist.

Every stone has 57 facets of the brilliant cut and I check them for every facet, three or fours times. It means every stone takes a lot of time. At this stage the polishing company will be able to predict with a high degree of accuracy the grade the diamond will ultimately achieve. It's now ready to be sent to the grading lab to be assessed.


The Diamond Guild of Australia is an association formed to establish and preserve benchmarks for ethics and quality in the sale and promotion of diamonds in Australia.


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