Cutting gemstones, also known as lapidary, is the process of turning raw, rough and polished stones extracted from the earth’s crust, into gemstones as we know them. Cutting a gemstone is the art of making the gem assume a certain shape that reveals and enhances its true colour, brilliance and lustre. Gemstone cutting is a skilled job that demands professionals to have remarkable experience. The best cut suitable to bring out the beauty of a natural stone relies on several factors, like the type, shape and quality of the rough gemstone. The cut of the gem directly affects its value as the cut determines how well a gem returns its body colour to the eye. The shape of the gem will dictate its overall look, but if it is faceted meticulously, the shape does not affect its value.
Gemstone cutters (also known as lapidaries) study the stone to hide it's naturally occurring flaws and highlight its unique charm.
The general categories of gemstone cutting are:
- Faceted gemstones: These are gemstones that have a flat, geometrical polished surface. This is the most popular style.
- Non-faceted gemstones: This category includes gemstones that do not have facets, like cabochons, beads, spheres, inlays, sculptures, etc.
All gemstones are cut and polished using progressive abrasion techniques using increasingly finer grits of harder substances. Diamond is the hardest naturally occurring substance, boasting a Mohs hardness rate of 10. It is used to cut and polish a vast variety of gemstones, including the diamond itself. Another alternative to diamonds is a man-made compound known as Silicon Carbide which has a Mohs hardness rating of 9.5.
The gem cutting process follows the following steps:
- Assessment: The first step is to analyse the raw gem to determine the best cut to enhance its clarity, colour, brilliance and lustre. The lapidarist examines the gem to strategically draw a plan to minimize inclusions and determine the placement of facets. For every gem, the lapidary aims to find the best compromise between the final appearance and the final weight retention (size in carat) as both these factors influence the value of the finished gem. The lapidary has to deduce the best way to achieve balance, symmetry and proportion in the finished gem.
- Slicing: A piece of raw stone is cut into a desired size to be carved into a gemstone using a diamond - tipped circular steel saw blade. A fluid substance such as water or oil is used to wash away any debris. This also helps in preventing the equipment from overheating, which can cause damage to the stone and the saw blade.
- Pre-forming: Also known as grinding, pre-forming involves removal of any obvious inclusions and impurities. The gemstone acquires a rough shape at this stage. A vertical steel grinding wheel is used to shape the gem. As with slicing, a liquid substance that acts as a coolant and lubricant is used in this process.
- Sanding: The gemstone is lightly sanded to smoothen its surface. Sanding is similar to grinding except that it removes material less rapidly, allowing more control. It uses finer abrasives to remove any obvious scratches left behind from the course grinding. This process requires time and precision as the stone is given its final shape during this stage prior to polishing.
- Faceting: Also known as lapping. This step involves faceting the gemstone. Maintaining the gem’s critical angle (the maximum angle of refraction) often results in a smaller gem. Sometimes size does matter and big can be beautiful; but that is not always the case.
- Polishing: After the gemstone is sliced and sanded to the desired shape and sanded to remove any marks, it is polished. Any irregularities or unevenness visible to the naked eye are eliminated in this final stage to give the gemstone a mirror-like finish. The finished gemstone is lustrous and brilliant. Lapidaries use very fine grades of diamond powder to prime the stone. Each facet is then individually polished to a high sheen, giving the stone a captivating lustre.
To explore the most popular styles of gemstone cuts, read this article on ‘Different types of gemstone cuts’