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 Post subject: Most difficult gem material to cut?
PostPosted: Tue Oct 16, 2012 2:51 pm 
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Hey guys, I was just randomly thinking about this last night. I know from personal experience that all else equal, a stone with stronger cleavage is harder to cut. But, I've only cut a limited variety of materials. So, I have two interesting questions that I hope might be educational for me, and any other newbies that have the same question. There's plenty of room for opinion here :mrgreen:

1. What factors make a gem material difficult to cut (in terms of the physical cutting process), and why?

2. What do you think is the single most difficult gem material to cut (in terms of the physical cutting process), and why?

*If your choice is something rare like apophyllite, then write that, but also include a more common one.


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 Post subject: Re: Most difficult gem material to cut?
PostPosted: Tue Oct 16, 2012 4:49 pm 
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Cerrusite for heat sensitivity. The ROM in Toronto has the "Light of the Desert" a huge faceted stone.

Road salt for softeness and aversion to water.


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 Post subject: Re: Most difficult gem material to cut?
PostPosted: Tue Oct 16, 2012 5:51 pm 
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I recently polished a baguette of a blue material represented by a customer as Tourmaline, but it did not polish like Tourmaline and had an R.I. matching Idocrase. The extreme ends of the baguette frayed even with a 3000 mesh lap. The stone had a parting or cleavage plane parallel to the table. This tended to chip out.
I could only get a consistent polish with diamond on a Darkside. The customer never gave me a positive identification of the stone.

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 Post subject: Re: Most difficult gem material to cut?
PostPosted: Tue Oct 16, 2012 6:42 pm 
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Try some villiaumite. Soft, perfect cleavage, and water soluble. Also reputedly poisonous in solution. Cuts a very pretty stone, small, pinks and reds, seldom unincluded. I've handled a few lovely dark red but transparent perfect little cleavages from Russia. Wish I'd kept one.

Saw a nice BIG faceted sulfur at the Detroit show last weekend.

Radioactives are certainly unpopular to cut, if not the most difficult. I have some euxenite-(Y) if you want to try; opaque but takes a high polish.

Cerussite as previously mentioned, will fracture from the heat of your hand. Wulfenite will fracture from the heat of your breath. (Ask me how I know that.)

FreakingCat had the most bizarre stuff... a faceted asbestos (!!!!!!???) and mica... his mica was an opaque black, presumably biotite, but there are transparent micas, like phlogopite, or maybe even lepidolite, that would look hella cool.

Realgar... gorgeous brilliant transparent red, but soft, and light sensitive, not to mention an Hg mineral. I have one that would cut.

Gypsum... common in big colorless transparent masses, sometimes nice yellows, but soft enough to scratch with a fingernail, flexible enough to be bent with finger pressure, cleavage almost as perfect as mica, and somewhat water soluble.

I hear carletonite is a real bear that will drive any cutter lucky enough to find a clear bit to early madness. Brad Wilson said it just goes to pieces when you touch it to the lap. Similarly rare and cleavable from the same locality would be serandite; wonderful pink color, very rare in transparent bits. Both very rare and very expensive in cut stones.

Amber (soft, but can't be that hard to facet, I cab Dominican with ease), vivianite, halite, sperrylite ($500 for a 5mm xl), all sorts of weird and wonderful minerals out there for you to play with - about 4,500 at last count.

I'm in the market for all of the above, if color, clarity, and price are decent. Let me know when you get 'em done.


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 Post subject: Re: Most difficult gem material to cut?
PostPosted: Tue Oct 16, 2012 7:52 pm 
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Icehut wrote:
Realgar... gorgeous brilliant transparent red, but soft, and light sensitive, not to mention an Hg mineral. I have one that would cut.


No Hg in Realgar. But, given its optical properties, I'd get a faceted cinnabar any day. :wink:

I also have a piece of realgar that would be facet quality. I'm not dopping it anytime soon, anyway. :D

Uhmmmm, back to the direct question of the topic. The most troublesome minerals I cut so far were calcite and apophyllite, with calcite being the most frustrating since I was able to get something acceptable until prepolishing the table. Then it was hell...

With more common minerals, I hate kunzite: I was able to get a good cut gems once out of 3 attempts... :roll: Some tourmaline-of-hell is a neverending source of frustration as well.


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 Post subject: Re: Most difficult gem material to cut?
PostPosted: Tue Oct 16, 2012 8:15 pm 
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DOH, just noticed that, As not Hg in realgar. Both are fun. I'd love to have a faceted cinnabar too, but never seen a crystal that wasn't too highly saturated.


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 Post subject: Re: Most difficult gem material to cut?
PostPosted: Tue Oct 16, 2012 8:32 pm 
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So far, the one that seems the most "worth it" to me is cerussite. I saw the pictures of it at the ROM, and DAYUM, that's nice. Crisp, bright, and dispersive.

In terms of difficulty, here's what I'm hearing so far:
Softness
Temperature sensitivity
Cleavage
Brittleness
Shock sensitivity


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 Post subject: Re: Most difficult gem material to cut?
PostPosted: Tue Oct 16, 2012 8:47 pm 
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Quote:
With more common minerals, I hate kunzite


I used to also, but finally figured the stuff out to where some were actually enjoyable.

The one that got me was apophyllite.
Not a chance.
Abandon Hope, all ye who enter.
Nevermore.
My Gemcutting version of Napoleon's retreat from Moscow.


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 Post subject: Re: Most difficult gem material to cut?
PostPosted: Tue Oct 16, 2012 9:53 pm 
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Apophyllite is a ba5t@rd one since it looks like a topaz. Yes, you see the cleavage, but it looks study. Then you touch your cutting lap. And after a few seconds you get a bunch of flakes all over your machine. :lol:

I'll try again some soft stuff. I'm making my own wax lap*, and I need some experiment with other laps/polishes**. I see a calcite in my late future. I definitely like (well) faceted calcite. And I'll cut one. :twisted:

* I'm actually thinking about making a wax+lindeA mixture a a "wax" base.
** The darkside should work well on some not too soft minerals.


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 Post subject: Re: Most difficult gem material to cut?
PostPosted: Tue Oct 16, 2012 11:09 pm 
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Arya Akhavan wrote:

1. What factors make a gem material difficult to cut (in terms of the physical cutting process), and why?

2. What do you think is the single most difficult gem material to cut (in terms of the physical cutting process), and why?

Please define "gem material."

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 Post subject: Re: Most difficult gem material to cut?
PostPosted: Tue Oct 16, 2012 11:34 pm 
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ROM wrote:
Please define "gem material."

For the purposes of this thread, any transparent mineral, natural or synthetic.


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 Post subject: Re: Most difficult gem material to cut?
PostPosted: Wed Oct 17, 2012 7:30 pm 
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Solid dihydrogen monoxide is theoretically about the worst you can do, especially cutting it with a wet lap. :twisted:

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 Post subject: Re: Most difficult gem material to cut?
PostPosted: Wed Oct 17, 2012 7:34 pm 
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gsellis wrote:
Solid dihydrogen monoxide is theoretically about the worst you can do, especially cutting it with a wet lap. :twisted:

Image


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 Post subject: Re: Most difficult gem material to cut?
PostPosted: Thu Oct 18, 2012 6:21 am 
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gsellis wrote:
Solid dihydrogen monoxide is theoretically about the worst you can do, especially cutting it with a wet lap. :twisted:


That's a good one! :D
But in fact this material is quite easy to cut, although it's mostly used for carving! :wink:

Image
Picture from: http://www.ice-impressions.com/

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 Post subject: Re: Most difficult gem material to cut?
PostPosted: Thu Oct 18, 2012 8:42 pm 
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Egor Gavrilenko wrote:
gsellis wrote:
Solid dihydrogen monoxide is theoretically about the worst you can do, especially cutting it with a wet lap. :twisted:


That's a good one! :D
But in fact this material is quite easy to cut, although it's mostly used for carving! :wink:

I would expect this from the guy who cuts sphalerite. :)

I still hold that using a wet setup is harder. Plus, your machine will be under operating temp. :P

Faceting Emperor challenge, Any SRB - material - dry ice (solid CO2)

Oh, and I always liked Jeff Graham's 'best' method for polishing halite... lick it.

Edit - someone said recently, "you need to think outside the box". Response, "There was a box?"

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