The Cutting Process

Like other industries, advances in technology have revolutionised the diamond manufacturing process. Computer applications and laser technology have allowed automation of many procedures. The result is a better quality of cut, faster procedures, less weight loss and the ability to utilise unusual rough, allowing new possibilities with shapes and allowing manufacturers to maximise profit.

PLANNING

The first step in cutting a diamond is undertaken by the planner or marker sometimes known as the designer. The responsibility of this important role usually lies with the most experienced master craftsman. The marker must have a thorough understanding of the internal structure of the rough and the directions of hardness in the crystal to determine the best outcome. They decide the most suitable cutting technique for that crystal, marking the plane of division with a black line. Their aim is to produce the biggest stone, with the best possible colour and clarity, whilst trying to achieve optimal proportions.

If a marker is not sure of the orientation of the crystal, they will polish a small window on the rough crystal to allow them to look inside the stone. This is particularly necessary with distorted crystal forms that show no visual expression of the internal symmetry. This step is the most crucial of all processes. Small errors could reduce the maximum weight yield or at worst, destroy the stone completely.

Computer technology has been developed to help the marker minimise some of the risks. Computer aided planning can offer suggestions for achieving the maximum profit from rough and can offer multiple solutions depending on the position of inclusions. The progress of the cutting can also be monitored along the way.
Insert pictures of rough crystals

Cleaving and Sawing.

After marking, the next step is dividing the crystal by either cleaving or sawing.  This procedure may be utilised to eliminate inclusions.
Cleaving involves splitting the diamond along one of its directions of weakness. Although diamond is the hardest natural substance there are some directions that are weaker than others. Diamond has four planes of weakness, which are parallel to the octahedral crystal faces. The atoms along these planes are not bonded as tightly together as those in other directions.

The cleaver makes a small notch called a kerf, in the diamond by using another diamond or now more commonly with a laser beam. The cleaver rests a knife-blade in the groove and gives it a firm blow causing the stone to split. Cleaving is breaking the diamond along one of its octahedral directions or cleavage planes.

Sawing is another method of dividing the rough crystal. Unlike the violent blow to the stone during cleaving, a mechanical metal saw is used to cut the crystal. The advantage of sawing is it can be done in directions other than the octahedral planes.

The advantage of sawing is that a crystal can be divided in directions other than the octahedral planes. The sawing directions are along one of the crystal€™s cubic planes or one of the dodecahedral planes.

The decision to saw or cleave is based on maximising rough and retaining profit. Sawing can cause greater weight loss from a stone, but it can be a useful option if an inclusion needs to be avoided.

Laser sawing was introduced in the 1970€™s as a more efficient process of dividing the crystal. There are many advantages to this method. A thin laser beam focuses on the diamond crystal. It heats along this line to such a high temperature that it vaporises creating a thin channel. Any included crystals of different orientation can be quickly cut through where previously they would have damaged saw blades and halted production. The laser sawing is a faster, more versatile method allowing several stones to be sawn at the one time. It produces smoother faces substantially diminishing excess weight loss and allows cutting in any direction. The marker has more creative freedom to plan rough according to size, shape and clarity, rather than crystallographic direction.

Bruting

After the division of the crystal, the bruting process is employed. By bruting, the diamond is given its basic shape, creating the rounded girdle outline whilst trying to keep the maximum girdle diameter possible. This process applies to only those shapes with rounded or curved girdle outlines. Squarer shapes such as princess and emerald cuts are not bruted.

Two diamond crystals are firmly set in a rotating lathe; the corner of one of the diamonds is slowly and carefully pressed against the other rotating crystal. as they turn a circular outline is achieved. Bruting is a process that should not be rushed otherwise small feather-like fractures will appear at the girdle edge. This can potentially lower the clarity grade and is known as a bearded girdle.

Lasers have also been introduced into this cutting stage. From the early 1990€™s lasers have been used for the cutting of fancy shapes. Laser bruting achieves shapes that are precise and symmetrical, without excess wastage. Most fancy shapes are now bruted using this method

Polishing

Polishing is the process also known as faceting; the last phase of the cutting process it involves placing specific shaped facets at the correct angles and location on the stone.

A large polishing wheel called a €˜skaife€™is coated with fine diamond powder that fills the porous openings of the cast iron wheel. The addition of an adhesive makes the diamond powder stick to the wheel.

When polishing a round brilliant cut, blocking is the first part of the polishing process. The initial 17 €“ 18 facets that consist of the table and sometimes the culet, plus eight main crown and eight main pavilion main facets are placed. The process of blocking must be done precisely as it establishes the diamonds basic symmetry. Careful attention must be given so the pavilion facets and the crown facets are aligned at the girdle. Any cutting to correct symmetry errors would result in significant weight loss.

Some diamonds at this stage are complete, they are known as single cuts. The stones that are to be fully faceted are sent to the €˜brillianteer€™. It is their responsibility to polish the star facets, upper girdle and the lower girdle facets in a process known as €˜brillianteering€™. The brillianteer may also at this stage, facet the girdles for fine quality stones or to camouflage thicker girdles.

Automation is also prevalent in this final stage of faceting. Polishing machines with sensors are able to register a diamond facet being polished and then adjust the orientation of the diamond stone accordingly.

Modern advancements in technology have eliminated the need for human intervention in many areas of the cutting process. There are numerous advantages for the industry. Benefits include a superior quality of polish, increased efficiency which helps keep production costs down, maximising profit.