Getting the Best Gem Yield from a Crystal

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PinkDiamond
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Getting the Best Gem Yield from a Crystal

Post by PinkDiamond »

This isn't exactly home brew equipment, but it didn't belong under the cabbing or faceting machines either, so I settled on this one. :lol:

This article by Jeff Graham is excellent for getting the best yield from your rough, with some ideas you may not have thought of, so I hope all our cutters find it helpful. :)

Getting the Best Gem Yield from a Crystal
by Jeff R. Graham

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This large aquamarine crystal from Pakistan weighs 186 cts and measures 26.5 mm ⨉ 54.8 mm ⨉ 11.2 mm. It has a good, solid medium-blue color. Other than the growth line and a little spot next to it, it’s clean.

"Cutting rough crystals for the best gem yield is a critical skill for faceters. Not surprisingly, novices often ask me how they can figure this out. I’m going to walk through my decision making process, using the very nice aquamarine crystal above. (Previously, I discussed this crystal in an article on calculating how much money you can make from cutting rough).

So, let’s say I’ve bought this aquamarine rough. How do I cut it for the best gem yield?

Take Your Time

Examine the crystal very closely and take your time. Don’t make any fast decisions. If you’re not sure, just give it as long as it takes. Sometimes, I think about a piece of rough for a long time. Once, I mulled over a piece of spinel for a year before I cut it. I finally found the design it needed.

This quality piece of aquamarine will yield very high in about any shape(s) you want. However, you still face a lot of choices. While some depend on the best mass yields, others depend more on what you want to get out of the crystal, particularly what shapes.

Consider the Gem Shapes

I say shapes because I often opt for a lower yield to get a shape or design I want or that I know will work especially well for the rough. Some shapes just sell better than others, too. Always consider this factor. I usually try for shapes such as trillions, square cushions, and cushions. I also try for matched sets of about any type.

In the photo below, I’ve marked a basic set of outlines I would cut from this aquamarine. Keep reading. You might find some of my approaches to this crystal surprising.

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Choosing the Direction of Your Cuts

For this rough, the first cut is obvious. Cut the crystal along the growth line. You’ll get two pieces: one a little over a ⅓ of the length of the rough (left), the other a little under ⅔ of the length (right).

The main stone outlined on the left side section is a trillion. (For this gem, I’d use my Signature #4 design, one of my favorites for aquamarine).

Take a look at the following closeup photo of the left side section. Notice the flaw in the middle of the crystal, where the arrowed line starts. (The larger right section is clean, without flaws). Now, notice what looks like a flaw beneath the arrowed line? That’s only a reflection of the actual flaw, which is oriented and running at about 45° towards the crystal’s edge. The point of the pear outline also happens to point to the crystal edge that way.

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If you look at the next photo, you’ll see that cutting at a 45° angle with a saw blade will just about preform the pear pavilion (on one side) and, of course, help point up the trillion bottom. Note: I rotated the trillion a bit to get a long side along the saw cut. Due to the 45° cut, you’ll get a pear quite a bit bigger than if you’d just cut at 90°.

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... "

https://www.gemsociety.org/article/gett ... d-crystal/
PinkDiamond
ISG Registered Gemologist


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Re: Getting the Best Gem Yield from a Crystal

Post by SwordfishMining »

I saved that one. Im going to get to that Facetron learnin' one of these years.
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mick
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Re: Getting the Best Gem Yield from a Crystal

Post by mick »

I love crystal. I guess nowdays its not worth much, but when you see those old pieces, bowls and things that were cut from a natural stone, they are amazing.
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