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Gemstone Quality


#1

All, Do you have a standard for judging the gemstones you are about
to purchase? I suggest you develop a standard. Here is the how I
judge a gemstone and the reasons for what I am looking at. Equipment
needed : 10X loop, sliding calipers, and gemstone tweezers.

  1. I look at the color of the stone. Holding the stone in the
    tweezers over a padded surface I look at the general color saturation
    of the stone. Especially noting color zoning. The reasoning is that
    you can do nothing to improve the color of the stone without treating
    the stone.

  2. I look for inclusions in the stone. Using the 10X glass and
    holding the stone in the tweezers I turn the stone upside down and
    look for inclusions through the pavillion. The reasoning is that
    looking through the pavillion I do not get reflection off the facets
    and I can readily see inclusions that affect the value of the stone.

  3. I look for cutting problems. Is the stone windowed, is the stone
    symetrical, is the stone proportional, is the table centered on the
    pavillion of the stone, is the girdle even all the way around the
    stone? I use the sliding calipers to measure the stone for symmetry
    and to check for depth proportions. The reasoning is that any
    deviations from standard cutting practices using the physics of
    light reduce the reflection within the stone. You are looking for
    approximately 60-70% of the total depth of the stone below the girdle
    and 30-40% above.

  4. Holding the stone in the tweezers I use the loop to inspect the
    surface polish of the facets and the accuracy of the cutting. This
    take some training. You must learn to look at the surface of the
    stone and not at the sparkle. Once you master this you will
    immediately see the polishing scratches caused by using worn laps,
    incorrect laps, and poor polishing methodology. The reasoning is
    that polishing and accuracy of facet placement are what really adds
    to the cost of producing a gemstone. Both take time, expertise, and
    good equipment. Polishing and accuracy is where most lapidaries cut
    the corners to save money and sell their stones cheaper.

These four items will allow you to judge the stone in front of you.
If you do not understand the process and are at gemshow where I am
showing you are welcome to stop by and I will demonstrate the
procedure. If not and I can help over the Internet email me and I
will go into more depth.

Gerry Galarneau