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How to Polish Gemstone Facets

DaeA Roboter Automatic Gem Faceting Machine
DaeA Roboter Automatic Gem Faceting Machine

A good many cabbers who go on to faceting become very perplexed, and sometimes downright angry, to find that a little innocent piece of quartz — which anyone could polish to perfection in a minute if rounded — suddenly has developed all sorts of preculiarities just because it has flat facets. As they continue in the faceting craft they soon find a lap-and-polish combination that takes care of quartz with fair reliability. Then, one day, they try to cut a Peridot gem and find themselves as far as polishing is concerned — a beginner again. At the moment I have before me a collection of 16 gems, each of a different material, all requiring a. different polishing treatment. To name a few, there is amblygonite, opal, fluorite, rhodochorsite, calcite, apatite, diamond, and barite. Thus having been a beginner many times, I evolved a system for minimizing learning time with a new material.

For a starter I take a reference book such as Faceting for Amateurs by Glenn & Martha Vargas, or Gem Cutting by John Sinkankas, and note any hints and recommendations for polishing the material. I particular note its hardness because, based on my own experience and that of others, I know that materials of like hardness will often respond to like treatment. I also know that materials in the hardness range of from five to eight can probably be polished on a tin or tin-lead lap using Linde A or .04-micro alumina polishing powder, or perhaps cerium oxide. Below this hardness range a wax or a pitch lap may be necessary, and above it diamond powder on copper may be the answer (mandator for a hardness of nine or more).

Having chosen a tentative lap and polish combination, I then cut a flat area on a practice piece of the material, or the table area on the piece I’m going to use, and give it a try. If I run into a lot of very fine scratches that don’t want to fade away with variations in lap speed, pressure, or amount of water drip, I next try a different polish on the same lap, and perhaps try adding a few drops of detergent to the polish mixture. Numerous very fine scratches usually occur because the material will not respond to the particular polish being used. But suppose only a few fine scratches show up? In this case the best bet is to keep on trying with the same lap and polish, but with varying lap speeds and pressure.

Ultratec V5 Classic Gemstone Faceting Lapidary Machine
Ultratec V5 Classic Gemstone Faceting Lapidary Machine

What if the area polishes beautifully except that one or two deep scratches (almost gouges) suddenly appear? I’ve never found a satisfactory explanation for these, but agree they are the most aggravating thing that can happen to a facetor. They are so deep that polishing them out on a nearly finished gem invariably spoils facet meets and requires re-cutting part of the gem — if anything like perfection is desired. On the other hand, they are just as invariably taken care of by changing the direction in which the lap sweeps across the facet. It may take a few trials to find the proper direction, but try at right angles to the scratches first. Once found, make a note of which facet and what direction, so that if you must recut you will not run into the same trouble again.

Now suppose you find a lot of scratches, not very fine ones and definitely not the gouge type. Chances are that a change in lap is indicated. If you are using micarta or lucite, try a tin or a tin-lead lap or vice versa. If this doesn’t work and you are using cerium oxide, try Linde A or .04-micro alumina. If you still are having trouble, and the material has a hardness of around five or below, switch to a wax or a pitch lap.

In the long run it is better to learn something about how to polish an unfamiliar material before cutting the gem itself. Cutting facets is easy, Polishing them is often a different story. I once spent an entire day learning to polish a material I had never cut before, and was glad I didn’t do my learning after cutting the facets.

As a final word I’d advise this: Do not polish any facet longer than necessary. This means using as fine a pre-polish lap as you have available, preferably a 1200 or even a 3000 mesh lap. It also means cutting each facet as perfectly as possible and, above all, quickly making any angle or cheater adjustment that is needed to get that facet flat on the polishing lap. Never let the polish start at one edge of a facet and then creep across it. To do so will change the facet and shape, and spoil its meets with adjoining facets. Polish the whole surface once and for all, perfectly and right now!

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