The Cut of a Diamond
Transforming rough diamonds into the bright, sparkly gems with which we are so familiar did not begin until the fifteenth century. The early discoverers of diamonds in India over 2,500 years ago, focused on the double pyramid, octahedral crystals, as shown here, but of course broken crystals were also discovered and some of the natural facets on these stones showed how a diamond could sparkle if only it - could be cut.
It was not until early stone cutters discovered that you could use another diamond, and the diamond dust generated by the process, to grind facets onto the stones that the path towards the modern brilliant cut diamond began.
The first cuts were random flat shapes dictated by the original shape of the crystal, in which only the minimum of diamond was removed to create facets. Even at this early stage it was noted that some stones were brighter than others and it was then only a matter of time before the cutters discovered the best arrangement of facets to maximise a diamonds ability to bend light. It is this effect, called refraction that helps to produce the flashes of brilliance that we call the fire of a diamond.
 Rough diamonds are sorted into over 5000 different categories of shape, colour and clarity and in many cases more than one polished gem will be cut from a single piece of rough.
There are six basic shapes of rough diamond. These are called: stone (1), shape (2), macle (3), cube (4), flat (5) and cleavage (6).
The prime object of the cutter is always to achieve the best sparkle or brilliance and the maximum size diamond or 'yield' from the rough.
On average however this will only use 35% to 43% of the rough diamond, depending on
shape of cut. None of the residues are wasted and every last chip will be used in some form as part of the manufacturing process.
Cutting a diamond is a highly skilled task, which takes many years to learn. Whilst technology has taken over some aspects of the job it is still very much 'hands on' and the first task for the expert cutter is to mark the first cut on the rough crystal with Indian ink.
The factors that he will consider are the position of any inclusions (imperfections within the diamond) and internal features. He will also consider the proportions to achieve maximum yield and the direction of 'the grain', for like wood diamonds have a grain.
If the first cut is to be made along the grain then the stone can be cleaved or split with a sharp blow on a prepared groove, just as you would split a log. However if the cut is across the grain then it will have be sawn with a ferrous bronze disc spinning at 5000 rpm and charged with diamond dust (See A).
The next stage is to put the first round edge to the waist, of the stone, this lathe process is called bruting. (See B). After this process has been completed the stone will be returned to the manager to be assessed again and to check that the basic angles are correct and if necessary adjustments will be made. The rest of the process is carried out on a flat wheel (See C) and the facets are applied.
 Today there are many different 'cuts' or shapes of diamond but the most popular are: Brilliant (1), Oval (2), Marquise (3), Pear (4), Emerald (5) and Heart (6).
The angle and placement of the facets used to create these distinctive cuts have been developed over many years and are very precise, however as in all products of nature the raw material has an infinite variety and the great skill of the cutter is to achieve the maximum yield in weight and come as close as possible to ideal proportions as any deviation will have an effect on the value of the finished gem. |
