Jewelry has been a part of our lives since the dawn of civilization. "The oldest jewelry items known are three fish vertebrae necklaces found in a grave in Monaco, from between 25,000 and 18,000 BC" (GIA, Colored Stones 15.2, 1987). Other examples of early adornments include a necklace of cowrie shells and nephrite jade found in Iraq dating from about 5000 BC, and the burial headdress and jewelry of Queen Pu-abi from around 2500 BC from the Royal Tombs at Ur. Jade carvings have been found dating from about 4500 BC.
Our ancient ancestors first learned to chip, then drill and scratch wood, bone and rocks, and later learned to polish stones by rubbing them with sand (quartz). Around 3000 BC, Mesopotamians were using primitive lapidary wheels to shape and polish gems: mainly the softer ones such as turquoise, chalcedony (quartz) and lapis lazuli.
Diamond was the first gemstone to be routinely faceted, probably starting in Europe around 1300 (GIA, Colored Stones 17, 1987).
There are several ways to finish stones for ornamentation.
Tumbling is the simplest, where rough stones are placed in a barrel (or vibrating tumbler) with abrasive grit and water, and allowed to tumble over days or weeks. Finer and finer grits are subsequently used until the stones are polished.
Cabbing is a process where the rough stone is first sawed into a flat slab, then trimmed to the shape desired. When the back is flat, a dop (usually a wooden dowel) is adhered to it with dop wax, and the stone is moved slowly against grinding wheels of coarse to fine grit and then to polish to produce the smooth shine we expect.
Carving and engraving use the same principles with a variety of tools to rough in the shape, smooth with finer abrasives, and finally polish.
Faceting is the process of cutting and polishing a gemstone using flat faces (facets) in a regular geometric pattern.
There are a number of companies manufacturing faceting machines, each having its own unique design. They all involve a revolving lap with grit (abrasive) and a mechanism for moving the stone on the lap. Many have a fixed mast attached to the head to which the dop and stone are attached. Most of the laps require the use of coolant (water) to preserve the life of the lap and to protect the stone. There is a mechanism to set the desired angle vertically for each tier of facets, and an index gear to set each facet horizontally.
Accessories include laps with coarse to fine grits (100, 325, 600, 1200, 1600, etc.) and polishing laps of various kinds (cerium oxide, "Spectra", "Last Lap", Ceramic, Tin-Lead, etc.). The dop sticks have various size tops, and come in flat, vee, and cone shapes. There is also a transfer jig and a 45 degree table dop.
I. SELECTING A STONE TO CUT
GEM IDENTIFICATION - WHAT KIND OF STONE?
It is essential to identify the stone you’re cutting before you begin. A number of tests are useful for this. Three important properties are described here.
Most gemstones have a hardness of 7 or higher on the Mohs scale.
SPECIFIC GRAVITY (SG)
The specific gravity of a stone can also help you identify the material. The specific gravity is expressed as a multiple of the weight of an equal volume of water. For example, sapphire has a SG of 4.00, so a one-milliliter size sapphire weighs four times as much as a milliliter of water.
SG testing liquids usually include the following: 2.57, 2.62, 3.05 and 3.32. These will allow tests of many of the common gemstones. Quartz is 2.66, emerald 2.68, topaz 3.53.
REFRACTIVE INDEX (RI)
The refractive index is a good clue in your identification of a stone. Refraction is the bending of light when it enters a gem. The refractive index (RI) is a measure of the ratio of the speed of light in air to its speed in a gemstone. Each gemstone has an identifiable RI.
The RI of a diamond is 2.417, so light travels almost 2 1/2 times as fast in air as in diamond. Thus, the slower the light travels in a stone, the higher it's RI. Generally, the higher the RI, the more sparkle you can expect in a well-cut stone.
In a singly refractive (SR) stone, the light moves at one speed in any direction, but in a doubly refractive (DR) stone, the light moves in two directions traveling at different speeds. Doubly refractive gems have two RI's.
Examples of SR stones: Diamond 2.417, Garnet Group 1.72 to 1.81, Spinel
Examples of DR stones: Corundum (Sapphire and Ruby) 1.76-1.77, Tanzanite 1.69-1.70, Peridot 1.65-1.69, Tourmaline 1.62-1.64, Topaz 1.62-1.63, Beryl (Emerald and Aquamarine) 1.57-1.58, Quartz 1.54-1.55
II. CHOOSING A DESIGN
You have now located a stone that you would like to facet. Since you know what kind of stone it is, the knowledge of the hardness will assist primarily in choosing the polish lap and polishing material. It also will guide you in choosing the initial lap to rough in the stone. The RI will give you a range to use for the design angles to avoid the window (or fish eye). You will also know if orienting the stone in a certain direction is advisable, especially with DR stones.
BRILLIANCE: Are you primarily concerned with the brilliance of the stone? Do you want lots of sparkle to impress your friends? If so, you'll want to use a light colored stone and a brilliant cut (round, oval, barion, radiant).
COLOR: Or would you rather have a beautiful deep color, as in a deep purple-red Siberian amethyst or a deep blue-green aquamarine? Your stone will probably lend itself to a deep emerald cut to enhance its color.
WHERE TO LOOK FOR IDEAS AND DESIGNS
PUBLISHED DESIGNS: There are many published designs and books of designs by a number of well-known authors. Some of the best known are:
Faceting for Amateurs and Diagrams for Faceting, Vol. 1-3 by Glenn and Martha Vargas; Facet Design, Vol. 1-7 by Long & Steele; Star Cuts, Vol. 1-5 by Fred Van Sant
There are also many faceting guilds and groups with newsletters offering new designs on a regular basis.
DATAVUE2: This program, created by Robert Long and Norman Steele, is a database of over 3000 published facet designs. If you would like DataVue2, it can be downloaded from the Internet for free here. If you already have DataVue2, but didn't update to the latest version, it is also available here.
GEMCAD for Windows: In addition to published designs, there is a new version of GemCad available so faceters can improvise and create their own designs. It has been created and published by Robert W. Strickland from Austin, TX. With this program, you can draw your own design and the program will print out the angles and index numbers needed to cut the stone. You can download GemCad by clicking here.
The initial preforming can be done with a trim saw, to get the unwanted sections out of your gem rough. If the stone is about the size you need, you can use a rough wheel on a cabbing machine to preform the stone with a flat top, sides that approximate the shape you (or the stone) have chosen, and a bottom that tapers to a point (culet) or to a keel line (for emerald cuts). Then the top can be flattened evenly by holding the stone upside down over a rough lap on the faceting machine. This will allow the dop to adhere more effectively.
Dopping is the process of affixing your stone to the end of a brass dop stick (dop) about 2 inches long and 1/4 inch in diameter. This is often easier said than done, as the stone must be perfectly immobile while the pavilion (bottom) is cut, but then must come off after transfer without damaging the stone or weakening the bond. The types of adherents usually used include a combination of dop wax (black or brown), superglue, and epoxy.
PAVILION AND GIRDLE: The pavilion is first roughed in using a 100-325 lap. The smaller facets are cut and the stone is prepolished (325-1200). Then all pavilion facets are polished, including the girdle.
CROWN AND TABLE: Next, the stone is "transferred," which includes attaching a cone or vee dop to the just completed pavilion with epoxy, then removing the initial dop from the crown. The same process is repeated on the crown: roughing in, cutting all facets, prepolishing and polishing. The final step is cutting the table, using the 45 degree table dop. When the stone is competed, it is usually soaked in a solvent such as methylene chloride to remove the dop. The result can be magic or disaster! You will learn something new from each stone you cut, and as you cut more stones a greater proportion will have the magic!
© 1994, 1997 MystiCrystals®
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