Diamond is one of the hardest materials known to man, so naturally this leads many people to wonder - how do jewellers cut them into such dazzling shapes? The answer, generally speaking, is that they use other diamonds. Diamond cutting and shaping is an incredibly specialised process involving many steps: the many-faceted gems you see adorning rings and necklaces don't get that way overnight!
Before any cutting or shaping is done, manufacturers will assess the potential of a rough diamond - that is, a freshly mined diamond in its natural state. In the past this would be done by eye alone, but modern techniques include using a scanner to create a 3D computer model of the rough diamond, from which the manufacturer can decide how best to cut and shape it.
The next step is cleaving or sawing. The rough diamond is placed in a cement or wax mould to hold it in place, before a sharp groove is cut into the tetrahedral plane (the weakest point). A sharp hit with a hammer 'cleaves' the diamond into smaller pieces: as diamonds are both incredibly hard and very brittle, they tend to split quite cleanly.
Alternatively, the diamond may be cut with a diamond saw or a laser, a process which takes hours. During sawing, the cutter will decide which parts of the diamond will become the table (the flatter 'face' of the gem) and the girdle (the outer edge with the largest diameter). Once the diamond is of the desired size, the facets of the stone are ground flat against another diamond - this can be done by hand (bruiting) or by machine (cutting).
Once the intricate work of cutting the facets is complete, the diamond is polished on a wheel called a scaif. The scaif is lubricated with an abrasive paste of olive oil and diamond dust that smooths out any remaining rough parts on the diamond. When this has been done to the cutter's satisfaction, the diamond is boiled in a solvent of hydrochloric and sulphuric acids to remove any dust and oil. The gemstone is now complete - ready to be mounted on a ring, necklace or any other piece of jewellery!
The process of diamond cutting is a long complicated work and this process is called Lapidary. It includes cutting, shaping, polishing, and setting of finished diamond into jewellery.
These days computerized machinery and laser technology is also used for diamond cutting. But technology is employed only in the cutting of some of the diamonds. Otherwise, cutting process is still done by hand. Cutting skill is passed on from one generation to another.
The Lapidary process is shown below in detail:
The first and vital step in the diamond cutting and polishing process is the analysis of the rough diamond. This step requires all-consuming imagination, skill and precision by an experienced diamond cutter. After analysing its size, shape, clarity and crystal direction, the best cut for the diamond is determined in order to maximise its end value and appearance. This step can only be completed successfully if done by a master diamond cutter whose trained eye and expertise affords him the ability to determine the best possible cut for the rough stone.
A diamond cutter will consider various possibilities before deciding which of them will yield the best quality gem, as it is a diamond's cut that determines its possibility to reflect light. Even if a diamond is graded well in terms of its color, clarity and carat weight, a poor cut will result in a dull effect, which greatly affects the value of the stone.
Diamond manufacturers analyze diamond rough from an economic perspective, with two objectives steering decisions made about how a faceted diamond will be cut. The first objective is that of maximum return on investment for the piece of diamond rough. The second is how quickly the finished diamond can be sold. Scanning devices are used to get a 3-dimensional computer model of the rough stone. Also, inclusions are photographed and placed on the 3D model, which is then used to find an optimal way to cut the stone.
The process of maximizing the value of finished diamonds, from a rough diamond into a polished gemstone, is both an art and a science. The choice of cut is influenced by many factors. Market factors include the exponential increase in value of diamonds as weight increases, referred to as weight retention, and the popularity of certain shapes amongst consumers. Physical factors include the original shape of the rough stone, and location of the inclusions and flaws to be eliminated.
The weight retention analysis studies the diamond rough to find the best combination of finished stones as it relates to per carat value. For instance, a 2.20 carat (440 mg) octahedron may produce either two 0.50 carat (100 mg) diamonds whose combined value may be higher than that of a 0.80 carat (160 mg) diamond plus a 0.30 carat (60 mg) diamond that could be cut from the same rough diamond.
The round brilliant cut and square brilliant cuts are preferred when the crystal is an octahedron, as often two stones may be cut from one such crystal. Oddly shaped crystals, such as macles are more likely to be cut in a fancy cut that is, a cut other than the round brilliant, which the particular crystal shape lends itself to.
Even with modern techniques, the cutting and polishing of a diamond crystal always results in a dramatic loss of weight, about 50%. Sometimes the cutters compromise and accept lesser proportions and symmetry in order to avoid inclusions or to preserve the weight. Since the per-carat price of a diamond shifts around key milestones (such as 1.00 carat), many 1.00 carat (200 mg) diamonds are the result of compromising cut quality for carat weight.
In colored diamonds, cutting can influence the color grade of the diamond, thereby raising its value. Certain cut shapes are used to intensify the color of the diamond. The radiant cut is an example of this type of cut.
Natural green color diamonds most often have merely a surface coloration caused by natural irradiation, which does not extend through the stone. For this reason green diamonds are cut with significant portions of the original rough diamond's surface (naturals) left on the finished gem. It is these naturals that provide the color to the diamond.
The other consideration of diamond planning is how quickly a diamond will sell. This consideration is often unique to the type of manufacturer. While a certain cutting plan may yield a better value, a different plan may yield diamonds that will sell sooner, providing an earlier return on the investment.
Once a full examination of each rough diamond has been carried out, the stone is marked to decide how it should be cut to yield the greatest value. At this stage, the shape of the rough diamond and the number and location of imperfections must be considered. The marker or planner must determine the direction of the cleavage (or grain) in the diamond. Due to the diamond's atomic structure, it can be cleaved in four directions parallel to the octahedron crystal faces.
If the planner decides the stone should be cleaved, it then goes to the cleaver. Large diamonds are often pre-shaped by cleaving into pieces suitable for sawing. For stones that are considerably large and valuable, cleaving is critical as a mistake by the planner or cleaver could shatter the stone. Using another diamond as a cutting tool, a groove is cut along the line showing where the stone is to be cleaved. The cleaver mounts the diamond in a dop, or holder, inserts a steel wedge into the groove and strikes the wedge sharply with a mallet to split the diamond along its cleavage.
The third stage (or second if cleaving is unnecessary) is sawing. The specialised saw is a paper-thin disc of phosphor bronze, rotated on a horizontal spindle at about 4,000 revolutions per minute. Mounting the diamond in a dop, the sawyer clamps the diamond so it rests on top of the blade. The rim of the saw is charged with diamond dust, so that as the sawing continues, the blade continues to recharge itself with diamond from the crystal being cut. The saw is able to cut through a 1.00 carat rough diamond in 4 to 8 hours, but if it hits a knot, the process may take much longer. Each diamond is unique and its cutting angles need to be planned with mathematical precision in order to achieve the desired result.
Today many diamonds are cut using laser equipment which is far more accurate and efficient. The laser saw revolutionised diamond cutting when it was introduced in the 1930s. The stone is mounted onto a dop (similar to those used in conventional sawing) for passage through the powerful laser beam, whilst the progress is monitored on a screen. The burned graphite from the high-temperature laser leaves a black mark around both sides of the stone where the laser cut through. Therefore, these sides then need to be polished. In certain cases, more weight is lost than would have been with conventional sawing.
The biggest advantage of laser cutting is its precision. There is no cutting edge to wear down, and lasers are less likely to warp the diamond because the heat is confined to such a narrow space. Since this method causes less friction on the stone, it is also safer - although temperatures are extremely high. Efficiency is also an advantage, as less manual labour and higher-speed technology means speedier production is possible.
This step is called girdling, and may also be referred to as rounding or bruting. The stone is placed in the chuck of a lathe and as it spins, a second diamond mounted in a dop at the end of a long handle is held against it. This process slowly rounds the diamond into a cone shape.
After the diamond has been girdled it is sent to the lapper, or blocker, who specialises in placing the first 18 main facets on a brilliant cut diamond. It's done on electric motor driven revolving cast iron polishing disc. The disc is charged with diamond powder. The diamond to be polished is held by a clamp and facets are polished one by one. For some small diamonds the process stops here, but larger diamonds go on to a specialist brillianteer to have additional facets polished, adding to the brilliance and fire of the diamond.
Next it is sent to the brillianteer who creates and polishes the remaining 40 facets (star, upper girdle and lower girdle facets), when the diamond is being cut in the standard 58 facet brilliant cut. For placing and polishing, the stone is set either in a lead dop or a mechanical clamp and held down on a revolving cast-iron lap (a horizontal, circular disc) that has been charged with diamond dust. Extra care is required at the faceting stage because the angles of the facets must be exact in order to yield maximum brilliancy, and their sizes must be accurately regulated to preserve symmetry, in order for the diamond to reflect the maximum amount of white light. The more sparkle and brilliance a diamond has, the more beautiful it is, and the higher its value will be. It is this step that determines the fire, brilliance and scintillation the diamond will have.
Once the fully faceted diamond has been inspected and approved, it is then boiled in hydrochloric and sulphuric acids to remove any dust and oil. It is then considered a finished, polished diamond. Such loose diamonds are then ready to be distributed to wholesalers, manufacturers and retailers to create products for the diamond shopping consumer.
Due to changes in market desirability and popularity, the value of different styles of diamond fluctuates. All diamonds can be recut into new shapes that will increase value at that time in the market and desirability. An example of this is the marquise cut diamond which was popular in the 1970s to 1980s. In later decades, jewellers had little success in selling this shape in comparison to other shapes like the oval or pear shape. The marquise can be cut into an oval diamond by any diamond cutter with a loss of 5 to 10% in total weight. For example, a 1.10 carat marquise shape would be a 1.00 carat oval cut diamond by rounding the sharp points and creating an oval which currently in the market has a much greater desirability and resale value. The same marquise shape also could become a pear shape instead by only trimming and rounding the side which will be turned into the base of the pear shape.
In the 18th century there was a trend for recutting Indian diamonds to suit English tastes. The Koh-i-Noor's original cut weighed a little over 186.00 carats. When it was recut to an oval shaped brilliant, almost 80.00 carats were lost.
Other aspects are affected in recutting for value as well, such as the clarity. If an original shape contained inclusions on the tips, the recut would yield an increase in clarity since trimming down to a new shape would yield a cleaner overall finished diamond.