Choosing your diamond
C1. Cut
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 crystal, 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 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 500 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).
You can see these shapes illustrated to the right
and some of the most likely polished styles that
can be created from them are illustrated further
down the page.
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 an
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 of 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 be sawn with a ferrous bronze disc spinning at 5000rpm 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 finished gem.
