The journey from a dull piece of rough to the sparkling stone we know is a long process, with several stages, each carried out by a master. This blog will take you through the main steps, and hopefully illustrate the skill and talent of the diamond cutter.
The initial stage is simply to plan what shape the diamond will have. As the “skin” of a rough diamond is usually frosted, a small window is polished on the surface of the stone to allow a cutter to look inside and see what the diamond is like. The size and position of flaws are noted, as are any internal characteristics which might give problems later. Today, there are some very high-tech computer programs which can map the inclusions and allow a cutter to manipulate the stone on a screen and calculate how to cut the stone to yield the largest diamond or diamonds. The use of lasers, discussed more below, means that you can cut several stones from one piece of rough. This is the major benefit that lasers bring; yields are improved, and waste reduced. It is important to note that lasers are not used in the polishing and brillianteering of a stone, which are the stages that give a cut grade. In large pieces of rough, it is possible to plan over ten polished diamonds. You can see below the gradual evolution from a rough stone, to two polished diamonds.
The jump in value at the magic markers is also relevant; the price difference between a 0.99 carat stone and a 1.00 carat stone is significant. However, there is no appreciable difference in the apparent size. Below is an example of the options one may be faced with. The centre image shows the first option, a large diamond (marked in blue) and a smaller diamond (marked in green). On the right, the second option is where the two stones are closer in size to each other. However, the larger diamond has a flatter crown, which could have a negative impact on the cut grade.
Cleaving is a method of splitting a diamond in two with a single blow. A line is drawn on the stone (see image above) to mark the position of the cleaving. The diamond has a small notch placed in it to mark the point of cleaving, and a cleaver with a rounded edge is used to split the stone. This technique is hundreds of years old, and works well because one works along the grain of the crystal. Lasers have become very helpful at this stage, as one can work around a flaw within the stone, and allows for unusual shapes of rough to be worked into a useful stone. The image below shows a typical computer plot of a diamond to be cut. The lime green areas are flaws within the rough, and you can see that the main area at the bottom centre of the diamond is being left alone. The data at the right gives the sizes and probable grades of each stone; all are H colour, and between VVS and VS clarity. A laser will be used to make the two cuts marked in yellow.
Cutting is shaping the diamond into its final outline. The traditional method is to fix the rough stone into the cup of a lathe. This is rotated at high speed, and another diamond is brought near, giving it the desired round shape. Today, a slight variation is used whereby two pieces of rough are rotated, and brought into contact, thereby shaping two stones at the same time. This is seen below.
Polishing is the act of putting facets onto a diamond. The diamond is clamped in an adjustable arm, and pressed onto a polishing disk. The disk is a horizontally spinning plate treated with a mixture of diamond dust and oil. As nothing in the world is as tough as a diamond, the only thing that can cut or polish it is another diamond. The dust from each cutting is therefore recycled for use in the next cutting. This is a most highly skilled step, as a miscalculation of only a few tenths of a percent can totally change both the weight and the cut grade of the finished diamond. Skilled brillianteers are in high demand, and to become a top cutter takes years of training.
By Hand or by Machine
An interesting discussion is whether or not a stone should be polished by hand or by a machine. Today, a combination of both is used; lasers are used to cleave the diamond, as they can work across the grain of the diamond. This reduces the waste, because as noted earlier you can make two diamonds from a piece of rough, a feat not always possible in the past. However, polishing, and particularly brilianteering, can only be done by hand. Also, a trained eye is important to oversee the process; sometimes you are faced with certain decisions, for example should you cut a 1.5 carat stone with a flaw, or a 1.2 carat stone and cut away the flaw? A knowledge of the potential beauty, marketability and value of stones is vital.
Automation is important to allow for the quantity of diamonds used annually to be cut and polished to a good standard. Below is a bank of diamond saws, which can be operated by one worker. This frees up many other cutters to work on the more complex and skilled aspects of the process.