GEM CUTTING TERMS

by Don Clark CSM

Lapidary is the art of working in stone. For some reason though, it is only applied to working with small, gem materials and is not extended to large objects, like Michangelo’s statues.There are four basic styles of gem cutting: tumbling, cabbing, faceting and carving. Plus there are a number of ways to assemble stones into mosaic like patterns, called intarsia, pietra dura, pietre dure, or parchin kari. They are used to make jewelry, boxes, and other ornamental objects.

TYPES OF GEM CUTTING

GEM CUTTING TERMSTUMBLING

The simplest form of gem cutting is tumbling. This is where the rough material is put in a revolving barrel with abrasives. Progressively finer abrasives are used, until a polish is obtained. This process closely resembles what happens to rocks in a stream or on the beach, except that the level of polish is much higher.

Tumbling is ideal for children. It is easy, takes a minimum of equipment, (approx. $100,) and the results are sensational! There are a number of inexpensive settings available so the tumbled stones can be turned into jewelry. These make wonderful, homemade gifts.


GEM CUTTING TERMS

CABOCHON CUTTING

Cutting en cabochon, or as it is more commonly known, cutting cabs, is probably the most common form of gem cutting. Cabs are gems that are cut with a flat bottom and a curved or domed top. If you can envision an opal or a piece of turquoise, you are looking at a cab.

Cabs have distinct resale value, based on the material they are cut from and their cutting can be profitable. This makes for an excellent, indoor hobby. It is especially enjoyable if you are cutting materials you have found yourself.

It only takes a little practice to become proficient and is something almost everyone can learn to do well. Good equipment will cost in the neighborhood of $1,000. A word of warning though, this can be highly addictive!


FACETING

GEM CUTTING TERMS

Faceting is the style of cutting that has the greatest profit potential. If you can envision a diamond, you are looking at a faceted gem. The surface of a diamond is covered with several geometrically arranged, flat surfaces. Each of these flat surfaces is called a facet. The gem is faceted, by a faceter on a faceting machine. This is also where we get the expression, “a multifaceted question.”

The purpose of faceting is to bring out the brilliance of a gem. That is where the light entering the stone is reflected off the bottom facets and returned to the viewer. Brilliance should not be confused with dispersion or fire, which is the multicolored flashes you see coming out of diamonds and some other gems.Faceting is one of those art forms that you can become good at with a minimum of experience, but also one where you will never run out of new challenges. Nor does it require any esoteric “artistic” sense. Machinists, engineers and people good at math often excel in faceting.Many faceters are semi-professionals. They sell enough gems to support their hobby, or to bring in some supplemental income for their family. For those interested in collecting or investing in gems, this is by far the most practical way to go. The price of rough and labor is almost always less than the wholesale price of the finished gem.If you want to facet gems, for fun or profit, expect to invest about $2,000 in tools to get started. Here, more than in the other styles, the quality of your equipment will greatly effect both the quality of your work and the enjoyment you get out of it.


GEM CUTTING TERMS

CARVING

Carving is the most challenging of the lapidary arts and there are very few recognized experts in the field. To be successful, one must have a distinctive artistic sense and a thorough understanding of the principles of lapidary. Unlike working in wood or metal, the materials present definite limits as to what can be done.

There are several types of carving. One of the best known is cameo. These are usually cut from sea shells or agates, but they can be carved from almost any material.

GEM CUTTING TERMS

 

GEM CUTTING TERMS

Often cabochons are carved. If the design is cut into the top, it is called an intaglio, or a relief carving. If the design is carved on the back, it is a reverse intaglio.

Some carvings are not designed to be used in jewelry; they are cut simply for their beauty. These are classed as stand alone carvings.

GEM NOMENCLATURE

GEM CUTTING TERMS

For both cabs and faceted gems, the top is called the crown. The widest part of the gem, the part that defines it’s outline, is called the girdle. Viewed from the side, the girdle is usually fairly thin.The bottom of a faceted gem is called the pavilion. The largest facets are called mains. There are both pavilion mains and crown mains. The large, horizontal facet on the top, the one that acts as a window into the interior of the gem, is called the table facet.

Adjoining the girdle are the break facets. Their purpose is to scatter light, creating more scintillation. There are both crown and pavilion break facets.

The top row of facets, those next to the table, are called star facets. Along with the other crown facets, they serve to control the entry and exit of light from the gem. The pavilion facets are designed to reflect the light back to the viewer.

SHAPES

GEM CUTTING TERMS

Fancy shaped gems are anything other than the standard. For cabochons, that is something other than a round or an oval. They include rectangles, rounds, squares, crosses, tear drops, and free form shapes.GEM CUTTING TERMS

The standard shapes in faceting are rounds, squares and rectangles. A rectangle with the corners trimmed off is called an emerald cut.

Ovals are considered fancy shapes, because they take more work to cut than a round. Heart and pear shaped gems take even more work.

Marquis or navettes are long thin gems, with gently curved sides, that come to a point on the end.

GEM CUTTING TERMSGEM CUTTING TERMS

Cushion are almost square or rectangular. Their sides are gently curved, like the cushions of your couch.

A shield is symmetrical from side to side, but not top to bottom. They come in a variety of proportions, with different numbers of sides.Other fancy shapes include, rhomboids and parallelograms, as well as triangles, hexagons, octagons, etc.

FACETING STYLES

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There are two basic styles of faceting. If you look at the round brilliant diagram, you will see it has triangular and kite shaped facets. This style is called a brilliant cut.A step cut features rectangular shaped facets neatly arranged, one on top of the other. An “emerald cut,” a cut cornered rectangle, is the most common example of a step cut.

These styles are often combined. The Ceylon cut has a step cut pavilion and a brilliant cut crown. This is an ancient technique and one still used in Sri Lanka today. Modern computer studies have shown that the reverse, a step cut crown over a brilliant cut pavilion, will often produce the greatest brilliance.GEM CUTTING TERMS

The barion cut was developed by South African diamond cutter, Basil Watermeier. Essentially, it is a method of putting a round brilliant pavilion into a fancy shaped gem. It usually has a step cut crown as well. This usually results in far greater brilliance than other methods. Interestingly, Mr. Watermeier discovered this just before the advent of computer ray tracing programs.

GEM CUTTING TERMS

The round brilliant pavilion, compared to other pavilion shapes, offers greater discipline of the light inside the gem. Barion cuts emit a fountain of light effect, that is quite striking!

Some gems combine faceting and cabbing. A gem with a faceted top and a flat bottom is called a rose cut. Occasionally you will see a gem with a faceted pavilion and a domed crown, but this is not a standard method of cutting.

CUT NAMES

GEM CUTTING TERMS

There are standard cuts that we all recognize, like round brilliants and emerald cuts. Most faceted gems are simply called by their shape. However, you need to recognize that there are many variations within each shape. A triangular gem can have several or few facets; lots or little brilliance and scintillation.

GEM CUTTING TERMS

Then there are other traditional, but less common, cuts with distinctive names. A good example is the Portugese cut. It has several tiers of facets, which creates a wonderful display of light. It has more scintillation than almost any other cut. As you can see from the picture, it requires many facets and requires considerable labor. That, plus the fact that the rough must have more than normal depth, makes it something that is used only occasionally.

GEM CUTTING TERMS

Still other cuts have no name at all. That is because faceters use what fits a piece of rough. It is not always a named cut – it is just what works. The red gem is a good example of this; it is a simple cut with a radiant pavilion.

In the 1980′s a program was released called Gem Cad. It allows people to test their cutting designs inside a computer before taking a stone to a lap. This made it easy for people to create new gem cuts and today there are now thousands of named designs.

Many of the newly named cuts are simply a means to standardize common techniques. For example, someone may “design” the cut used on this red gem. It then has an established method for cutting that can referenced and used again, rather than the faceter making it up as they go along.

While most of the new named cuts are just variations of standard cuts, some are unique. Indeed, there seems to be no end to the imagination of our lapidaries. There is no limit to shapes or the number and arrangements of facets. Some cuts are merging a variety of techniques. Below is a barion cut gem with a parallelogram outline.

GEM CUTTING TERMS

GEM CUTTING TERMS

CURVED FACETS

Flat facets are not the only technique available to today’s gem cutters. A popular style of cutting is called a “Fantasy Cut.” This technique uses large pavilion facets. Some simple grooves are used, which are mirrored through out the pavilion. This ametrine is an excellent example of a fantasy cut gem.GEM CUTTING TERMSBesides hand carving, there are now machines that will cut precision, concave facets. This requires considerably extra work. The gems are first cut traditionally with flat facets. Then they are transfered to another machine for an additional set of concave facets. The labor is so high, that this technique is unlikely to ever gain widespread use. However, as you can see from this picture, the results are nothing short of spectacular. The brilliance and scintillation exceeds anything that can be done with flat facets alone.

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There is no end to what an artist can do with stone. If you keep your eye open, you will see cuts that are totally unique.

See related articles by category: An Introduction to Gemology, Gemology, Reference Library

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