Diamond - Polishing (Cut) Process « BACK
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 diamond polishing(cutting) process includes these steps; marking or planning, cleaving , sawing, girdling or bruting, faceting or polishing, and final inspection or finishing.
Marking or Planning
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-carat rough diamond in 4 to 8 hours, but if it hits a knot, the process may take much longer.
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.
Bruting or Girdling
The following 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.
Polishing or Faceting
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. Next it is sent to the brillianteer who creates and polishes the remaining 40 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.
Finishing or final inspection
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.