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Tailler les Pierres Précieuses
Cut Gemstones

Processing Rough GemstonesIf you think of your job as a daily grind, imagine what life is like for a lapidary or gem cutter. Colored gemstones are very hard materials -- most are harder than steel -- and transforming them from the rough stone to a finished gem is a laborious process that involves a tedious combination of delicate and abrasive actions, all of this on expensive materials that are easily damaged.

The first stage in cutting a gemstone is to get the rough material down to the approximate size needed for the final gem, keeping in mind that as much as 65% to 75% of the original material will be lost in the cutting process.

Processing Gemstones manualIf the rough material is in large pieces, as in the case of quartz, it will first need to be sawn into smaller pieces. It is often necessary to saw more expensive materials as well into quite small pieces. Depending on the size of material to be cut, a circular saw covered with diamond grit is used, lubricated with oil or water to prevent overheating. These saws come in different sizes depending on the material to be cut. The larger saws are called slab saws while the smaller ones are referred to as trim saws.

The next stage in the process is to preform the material to the approximate shape of the final gemstone. This is usually done with a silicon carbide wheel. Most often a shape is selected that will maximize the use of the expensive rough material. Usually one side of the stone is cut with a flat surface; this will become the table or large main facet on the crown of the stone.

After the stone is preformed, it is mounted on a small stick called a dop. The top of the dop is flat and the stone is first glued to the dop on its flat side. The glue is actually a high temperature wax, making it easier to remove later simply by heating it and then cleaning the gem with alcohol.

At this point the lapidary can begin to cut facets on the gem, starting with the bottom half or pavilion of the stone. Though we talk about 'cutting' facets, this is actually another grinding operation, but one that must be accomplished with a high degree of precision. A horizontally mounted wheel called a lap is used, with different surfaces for grinding and polishing. The dop is held at an exact angle and then rotated to grind each facet in turn. Positioning the dop may be done with the mechanical arm and mast of a faceting machine or with similar but simpler devices still common in southeast Asia and India.

Polishing the facets to a mirror-like finish is done with a variety of polishing agents. These include very fine grades of diamond grit or aluminum oxide (corundum) as well as cerium oxide, tin oxide or chromium oxide. Polishing sounds like a simple job that anyone could do, but it is actually quite an art, with many trade secrets. The consistency of the polishing agent, the material of the lap and the rotational speed of the lap are all important variables.

  • First Published: April-03-2008
  • Last Updated: October-06-2010
  • © 2005-2014 GemSelect.com all rights reserved.
    Reproduction (text or graphics) without the express written consent of GemSelect.com (SETT Company Ltd.) is strictly prohibited.
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