Diamond rough

  • How a rough diamond is transformed into a polished stone

    The first stage in polishing a diamond is to the rough diamond into parcels based on the size and shape of the diamonds. The diamond sorters are not looking yet for stones to be either round brilliant or princess cut, but are instead looking for 'makeable' stones or 'sawable' stones.

    A ‘makeable’ stone is the name given to diamonds whose shape lends its self to having one large diamond cut from it. ‘Sawable’ stones are diamonds which can be cut in half in order to create two smaller diamonds.

    Each rough diamond is scanned into a computer using a Sarin machine. 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 choose to retain a greater proportion 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.

    The first facets to be polished are four in the pavilion and four in 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 is to make the diamond round. This is done using a bruting machine. Two diamonds are turned against each other to make the diamond round in shape. This process leaves a mat finish on the girdle of the diamond. The girdle can be left in this form, which is called a ‘bruted 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 up. 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 professional gemmologists. At this stage, the polishing company will be able to predict with a high degree of accuracy the grade that the diamond will ultimately achieve. It is now ready to be sent to the grading lab to be assessed.


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