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Author Topic: When to cut a slab?  (Read 450 times)

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John Robinson

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When to cut a slab?
« on: August 18, 2017, 12:04:10 PM »

I got a nice 64 Ct opal slab today in the mail. It has nice but thin top layer of color but a thick layer of color below overlying the rough.
The slab is less than 5 mm thick with some that being matrix. Is there a general rule about the limits of cutting slabs and general, the distance between two layers of color and the fact that one of the layers is sitting /set in the matrix?

Is that lower layer just fools' gold?
What is my next step?
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Orrum

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Re: When to cut a slab?
« Reply #1 on: August 18, 2017, 12:34:25 PM »

At thst thickness you should flat lap it and make your triplet.
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gemfeller

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Re: When to cut a slab?
« Reply #2 on: August 18, 2017, 12:47:47 PM »

If you haven't cut a lot of precious opal my suggestion is to buy some low-grade potch-and-color rough first for practice.  It will give you a much better idea of how opal color-bands are laid down and how to orient stones for  the best face-up color.  While you probably won't get many good stones from the P&C, the education you'll receive about precious opal formation and how to "follow the color" will be very valuable as you proceed to more expensive rough. 
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John Robinson

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Re: When to cut a slab?
« Reply #3 on: August 18, 2017, 02:24:25 PM »

Thanks! This might a good stone to practice with. I did not pay much for it.
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hummingbirdstones

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Re: When to cut a slab?
« Reply #4 on: August 18, 2017, 03:20:41 PM »

What I would do is grind just a wee bit off above that color bar so that you can see how it faces.  If it's a good bar, grind on down to it for a good cab(s).  Depending on how big the rough is, you may have to slice it into a couple of pieces to get viable cabs from the thickness.  It's better to have a few good, smaller cabs than one large cab that is too thin to cab correctly.
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Robin

John Robinson

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Re: When to cut a slab?
« Reply #5 on: August 18, 2017, 05:16:53 PM »

Well I went ahead and cut it because I did not pay much for it and I was going to have to take the matrix off in any event. (Plus there's that ancient question we all want answered What's inside that rock?)
It turned as well as can be expected the top weighs 18 cts and is thick enough to work and the bottom layer which was hidden looks good
I think(?)


RenderedContent-7695F958-656B-4B07-A3D2-8E1C9A25318F.JPG
*RenderedContent-7695F958-656B-4B07-A3D2-8E1C9A25318F.JPG (67.02 kB . 818x1136 - viewed 130 times)
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ileney

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Re: When to cut a slab?
« Reply #6 on: August 19, 2017, 08:21:34 AM »

Wow! That looks awesome!
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John Robinson

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Re: When to cut a slab?
« Reply #7 on: August 20, 2017, 08:22:51 PM »

The photo is enhanced, the camera does a poor job picking up color. Why I do not know so I have cranking up Contrast, Saturation and vibrance when I share opal photos. I would not think of using an enhanced photo to sell an opal without a disclaimer but if I just want to talk about an opal I think that enhancement lets others see what I see through my loupe
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ASO

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Re: When to cut a slab?
« Reply #8 on: September 14, 2017, 12:25:14 AM »

The top color looks pretty good its hard to tell but I would cut 2 or more stones.  If the body tone is even then I would cut a set or sweat from it to try and increase the value.  I wouldnt hold much hope for the bottom bar but if you have a .006 trim saw you could try and slice it off and use it for triplet material after flat lapping it.
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