Diamonds are the hardest natural substance on Earth, measuring a 10 on the Mohs scale. Diamond cutters use techniques such as splitting and polishing with a scaif or diamond saw to create sparkling gems, with up to 60% of the stone’s weight being lost in the process. The oldest technique is splitting, while the scaif was developed in the 15th century and diamond saws were added in the 20th century. Heat generated during cutting can cause gems to crack or explode.
A diamond measures a 10 on the Mohs scale of hardness, making it the hardest natural substance known to exist on Earth. This raises the question of how the stones are cut if they are that hard. There are a number of techniques used in diamond cutting, including basic splitting and the use of a grindstone called a scaif. These techniques have been developed over centuries of goldsmithing, and most cutters use techniques that were originally developed hundreds of years ago, because they are still the best way to handle gemstones. Diamond cutters usually combine several processes to create a sparkling, faceted gem from a rough stone, in a painstaking job where the stone can lose up to 60% of its weight.
The oldest cutting process is splitting. To cut a diamond, the cutter places a chisel into a weak spot in the stone and strikes it with a hammer, causing the gem to break. If the weakness has been misjudged, this can destroy the stone. If the diamond cutter judges correctly, the stone will be divided into workable pieces that can be individually finished. Medieval gem cutters would cut their cut stones with other diamonds, lubricating the surfaces with oil and smoothing the stone to reveal the facets. Some cutters still use other gems as part of their cutting and polishing process.
In the 15th century, the scaif was developed. A scaif is a polishing wheel that is kept liberally lubricated with oil and diamond dust. A cutter can use a scaif to polish a gemstone held in a dop, a cushioned backing that protects the stone as it is being worked on, revealing only the side that is currently being polished. The scaif changed the face of diamond cutting, allowing cutters to create symmetrical, uniform facets that bring out the gem’s true sparkle and luster. Playing with angles, the cutters have created unique and beautiful gems to be set in jewellery.
In the 20th century, another tool was added to the diamond cutting arsenal – a diamond saw. These saws are steel blades that are lubricated with a mixture of oil and diamond dust that is continually reapplied as the stone is worked. Because saws can generate a great deal of heat, the stones can be cooled as they are being worked on in special cooling stands. This is also the case with a scaif, and is one reason why cutting gems is such a painstaking process, because the cutter has to take a break every time the stone starts to heat up. If the stone contains water in small bubbles or cracks when it is cut, the heat can cause the water to boil and the gem could crack or explode.
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