Man has been fashioning gemstones for many years in an age-old quest to enhance the mystery and inherent beauty of nature's bounty. We examine the art of gemstone cutting and take a look at what makes a well-cut gemstone shine.

Gemstones are the gift of nature and are remarkable in themselves. However, their true potential is realized by a man's touch. This cutting releases the internal fire of the gemstone and creates the mesmerizing scintillation, which makes a gemstone so enticing to the human eye. This article explores the marvellous and highly skilled process that turns a rare rough gemstone into a work of art.

The Rough Gemstones

The whole process begins with a rough crystal. Crystals come in a variety of shapes and forms.

Some are still in their "crystal habit", while others were broken by the mining process, or by nature itself, by the twisting of the rock in which it was formed. Others are still alluvial and have the appearance of water-worn pebbles.

Less rare gemstones, produced in quantity and smaller sizes are often cut as calibrations. In the case of these cuts, the main consideration is a uniform size - an 8 x 6 mm oval for example. However, with rare, fine gemstones, the shape of the rough generally dictates the shape of the finished piece.

This is because fine gemstones are extremely rare and expensive, and a cutter will try to maximize the yield he gains from a rough piece to minimize loss of weight.

Hence, a short stubby gemstone may lend itself best to a round cut. In contrast, a long tourmaline pencil would almost certainly be cut as an emerald-cut, as this would be the cut that incurs the least loss.

Balancing the need to maintain gemstone weight and the importance of the right proportions to create a nice amount of light return is the cutter's eternal challenge.

Gemstones which are cut purely to maintain weight and do not take into consideration symmetry, beauty and brilliance are not considered to be top-grade, and a bad cut can ruin a very good rough piece.

The process of cutting rough stone into a scintillating Loose Gemstones are called faceting. This is a highly skilled process where a cutter places a number of facets onto the table and pavilion of a gemstone. To achieve this, the following steps are taken into consideration.

Planning the Cut

This is the most important step. In this, the cutter will consider the shape of the rough and the inclusions within the gemstone. Once he decides the "lie of the land", then he must determine how he will orient the cut, where the table will sit and where the pavilion will be.

Many things are taken into consideration here; any bad inclusions must be removed, colour zoning and banding, if present, will affect the orientation of the table as well the actual shape of the piece.

Once the cutter has examined the rough piece thoroughly, he will begin to clean the gemstone up. If a rough piece requires slicing, it will be done with a special machine.

Dopping & Preshaping

Next comes preshaping. It is done "freehand", the cutter holds the rough gemstone in his hand and grinds it using a spinning wheel called a "lap." Which will produce the very basic shape of the cut.

The preshaped rough piece is now attached to a special metal rod called a dop. A special dopping wax is used to do this. The dopped rod is then handheld by the faceter.

Faceting

This is where the actual magic is performed. Hundreds of tiny facets are placed on the table and pavilion of the preshaped rough gemstone. This is a specialized talent and skill which take years of practice to master.

The grinding lap is removed, and a faceting lap is now used, which is a much finer lap primed with fine diamond powder. The facets are placed on the gemstone at extremely precise angles. The skill and timing involved here are incredible.

Using the handheld faceter, the cutter uses the Height, Angle, Index triangle to place each individual facet separately on the pavilion and crown.

The angle will control the plane on which the facets are cut. Height controls the depth to which each facet is cut, and the index controls the placement of facets around the shape.

The pavilion and crown are essentially cut to form a lens and reflector. They gather and focus the light and reflect it back at the eye.

The crown facets form the lens, gathering light from all directions and focusing it on the pavilion which in this case becomes the reflector, bouncing light around inside the gemstone and then back upwards through the crown and out to the eye.

In fact, the same angles are not used for every gemstone. Different gemstones have different requirements, and a cutter must be aware of these.

This is because different gemstones have different critical angles. To explain this, the angles used for each facet denote the final result achieved, in that they affect the brilliance and reflection - a gemstone is capable of. Also, each facet's angles must be adjusted to maximize its optical performance.

The angles may vary based on the refractive index of the gem material, and all gemstones have different RI's.

Hence, when light passes through a gemstone and hits a polished facet, the minimum angle possible to reflect the light back is called the critical angle.

Suppose the pavilion of a gemstone is cut too deep or too shallow. In that case, the light ray will hit the facet outside the critical angle, and the light will escape outside of the gemstone. This is called unplanned light leakage.

Light Leakage

Gemstones with light leakage commonly display a "window" demonstrated in the picture below. This dull, unreflective area severely compromises the gemstone's beauty.

Two Oval Cut Tanzanite of equal quality showing how a window can affect beauty and light return.

The Left one is well cut with no window. While the Right one is cut too shallow with a large window. Because the pavilion is cut outside the critical angle causing light leakage.

Polishing

This is the last stage of the cutting process. The cutter uses a special polishing lap that is even finer than the faceting lap. It is primed with very fine diamond powder. Each facet is then individually polished to a high sheen, giving the stone a fine lustre.

An experienced gem cutter will perform each step with intuition and skill, leading to the asymmetrical, scintillating, beautiful finished piece.

It takes many years to achieve a high level of competence in this art. Highly skilled gem cutters are revered in the trade for their ability to visualize how a piece of the rough gemstone can be transformed into something of great beauty while balancing a host of considerations and challenges along the way.

What Can Go Wrong?

When you see a beautifully loose gemstone in a piece of jewellery, its beauty can be captivating. However, rarely, the sheer skill and risk involved in cutting rare gemstones appreciated.

Cutting rare gemstones like Alexandrite can be a risky business, indeed. So many things could go wrong along the way for the gem cutter.

He starts with a simple rough piece which can be very unexciting to look at and is faced with the task of transforming this into something exceptional.

Pre-forming is the first stage after the rough has been carefully assessed for inclusion and to determine which shape would best be cut.

This is a very risky stage as the rough is pre-formed by hand using a spinning faceting disk. Heat is also generated at this point, and often non-visible stress fractures can exist within a gemstone which can cause the gemstone to shatter or break at this stage.

This problem is not limited to coloured gemstones, and diamonds often cause great distress by performing the same trick on their beleaguered cutters!

So next time you look at a beautiful faceted gemstone, whether diamond or coloured gemstone, appreciate the great skill, art and pure miracle that it has survived several hundred million years under heat and pressure in the earth and then successfully navigated the path through the cutting process!

Author's Bio: 

Hey, this is Smitha Saam and I am a professional content writer or a blogger with experience of many years. Here you find educational and brand promoter content or articles.