How to Measure Gem Girdle Thickness

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How to Measure Gem Girdle Thickness

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Here's a good one for cutters, from the International Gem Society. There's a link to a second article that will help you learn how girdle thickness can affect diamond cut grading. Hope some of y'all find this useful. Enjoy! :)

How to Measure Gem Girdle Thickness
by Jeff R. Graham

Image
“Tourmaline Var. Indicolite,” 6 x 4 x 4 mm, 1.35 cts, Neuschwaben, Karibib District, Erongo Region, Namibia. © Rob Lavinsky, http://www.iRocks.com. Used with permission.

"Novice faceters often have trouble figuring out how thick to cut gem girdles. Of course, with experience, judging this becomes easier. To help inexperienced faceters, let’s first review the girdle’s function and the gem setting process. Then, we’ll discuss the best ways to measure gem girdle thickness.

The Gemstone Girdle

So, what purpose does the girdle of a stone serve? Simply put, faceters cut girdles on faceted gems so they can be set in jewelry. There are some other reasons, too, but this is the main reason.

For the gem to set properly, a girdle should be level, strong, and neither too thin nor too thick. (Easier said than done for a new cutter, I know). Let’s examine the setting process more closely. If you understand this process, you’ll better understand how to judge girdle thickness.

Setting a Gem in Prongs

When placing faceted gems in prong settings, jewelers will typically cut notches in the prongs, shaped to match the outline of the stone’s girdle as closely as possible. (Sometimes, prongs may have pre-cut notches, depending on the setting). The closer the notches to the shape of the girdle, the stronger the setting when done. See the graphic below.

Image

Once the notches are cut, the jeweler gently bends the metal prongs around the girdle to secure the stone in the setting. So, as you can see, girdle thickness plays an important role in gem setting.

If the girdle is too thick, the notches will have to be large and deep. This will likely weaken the structural integrity of the prongs. On the other hand, if the girdle is too thin, the notches will have to be small. They likely won’t hold well.

Study Blank Settings

You can easily find blank prong settings (without stones) online or at jewelry supply stores. Look at the prongs and pre-cut notches and visualize the girdle thickness you need. Remember, you’ll probably have to enlarge the notches to fit them to a specific stone before setting. Therefore, your final notches will be somewhat different and larger than the originals. However, a little research on your setting materials will give you a better idea of the girdle thickness you’ll need.

Girdle Observation Tips

If you’re evaluating a finished gem, here are a few pointers.

* Examine the gem from a normal reading distance.
* Put down your loupe and look at the stone’s girdle with your naked eye. (Viewing the girdle through the loupe will give you a false sense of size).

Is the Girdle Too Thin?

Does the girdle look sharp, like it might cut you? That’s the simplest way to tell it’s too thin.

Is the Girdle Too Thick?

Does the girdle look roundish? If so, it’s too thick.

What Difference Does Girdle Thickness Really Make?

Sooner or later, ... "


Other sections of the article include:
Girdle Thickness Percentages in Gem Designs
How do You Get a Decent Girdle Thickness?
Metal or Plastic Gauges?
Learning to Judge Girdle Thickness


https://www.gemsociety.org/article/righ ... thickness/
PinkDiamond
ISG Registered Gemologist


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