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#1 jrgpots

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Posted 16 April 2014 - 10:38 PM

I went over Ute Pass Colorado last summer. The east side of the mountain is granite but the west side is sedimentary rock. There was one layer of black heavily organic shale or mudstone.  I collected about 5 gallons of the stuff, brought it home, and ran it through the ball mill.  The first picture is of the raw material.  When water was added to the milled material it formed a clay.  It had poor plasticity.  I made a 10 cm bar of the black clay and bisque fired it.  It's color was bright orange Terra cotta.  I then fired it to cone 6 anticipating that it would melt before cone 6.  But as seen in the second picture it did not melt.  It vitrified and the surface is a bit shiny.  The color is a milk chocolate with a hint of orange.  The bar before drying was 10 cm long and after cone 6 firing was 9.7 cm.  There was very little shrinkage ( about 3%).

 

Does anyone have an idea what this stuff is? I looked up a Geological survey of the area which said it was sedimentary deposits from the tertiary age. There is a Molybdenum mine just up the ridge from this deposit. 

 

Any ideas how to make this a workable clay. As I said it is not very plastic. What would I need to add?

 

Jed

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#2 Tyler Miller

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Posted 17 April 2014 - 12:02 AM

Jed,  this is probably a dumb question, and it's probably just shale (or something I don't know), but does it have even a weak magnetism to it?  Do you think if you roasted the stone in a camp fire, it would be magnetic?  I probably just have iron ore on the brain and if so, I hope someone comes forward to correct me.

 

I've sent you some photos, via PM of a mineral someone posted to the little Iron Smelters group I belong to on Facebook, I can't post it here, because I really don't want to post someone else's photos in public without their permission, but they called the mineral siderite (iron carbonate).  I thought siderite was crystalline in form, like large crystals, but the photos shows more worn, sedimentary rock like you've got.  I thinking (more hoping) you might have an impure, shale-ish version of that.  It's lack of plasticity and extremely small shrink rate would support this, I think, maybe.  Possibly.  At the very least, it's not all shale.



#3 Roberta12

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Posted 17 April 2014 - 01:40 PM

Jed, this is sooo cool!   I am traveling with buckets from now on!   My Colorado roadside geology book says granite on the east side (which you figured out easily) and it mentions that there was a "dark gray Pierre shale, a soft fossil bearing rock.." 

 

 I wonder what sort of glaze you could make with your rock?   Might be really interesting!!

 

Roberta



#4 jrgpots

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Posted 17 April 2014 - 03:37 PM

Jed,  this is probably a dumb question, and it's probably just shale (or something I don't know), but does it have even a weak magnetism to it?  Do you think if you roasted the stone in a camp fire, it would be magnetic?  I probably just have iron ore on the brain and if so, I hope someone comes forward to correct me.

 

I've sent you some photos, via PM of a mineral someone posted to the little Iron Smelters group I belong to on Facebook, I can't post it here, because I really don't want to post someone else's photos in public without their permission, but they called the mineral siderite (iron carbonate).  I thought siderite was crystalline in form, like large crystals, but the photos shows more worn, sedimentary rock like you've got.  I thinking (more hoping) you might have an impure, shale-ish version of that.  It's lack of plasticity and extremely small shrink rate would support this, I think, maybe.  Possibly.  At the very least, it's not all shale.

 

It looks very much like your pictures. So it may have Mg  in it. That would explain the low shrinkage. I will try roasting some of the rock.  I do know that if I heat it up with a torch, it pops and explodes a little bit.  Nothing happens once it is milled.

 

 Roberta, my geology searching also mentioned Pierre shale.  I have two buckets of the granite as well.  It melts to a beautiful white.

 

 



#5 jrgpots

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Posted 19 April 2014 - 01:01 AM

Since this is a short clay body I thought about bentonite to the mix. Would I increase the bentonite in 2% increments (2%.4%.6%), and to what maximum percent?

In another thread, Marcia mentioned cat tail dander to prevent cracking of the clay when bending. This made me think of adding paper fiber.

I will mix some sample clays with different amounts of bentonite and see what I get.

Jed

#6 Babs

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Posted 19 April 2014 - 03:50 AM

The paper won't do anything for the plaasticity, prob  even be adverse to it.

Are you against corrupting it with a known plastic clay body??



#7 Benzine

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Posted 19 April 2014 - 09:45 AM

The paper won't do anything for the plaasticity, prob  even be adverse to it.
Are you against corrupting it with a known plastic clay body??


Yep, paper just adds strength, which is why it's good for sculptural works. It might hold the body together a bit better, than the body alone. But in regards to adding paper to make something more plastic, it just won't help. Someone asked about using paper clay for throwing a few weeks ago. The general consensus was that it wouldn't work well.
"Anything worth believing, is worth questioning"

#8 Tyler Miller

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Posted 19 April 2014 - 11:22 AM

I was thinking it would be a good source of iron for bodies and glazes, blended with clay from another source, or a natural flux.  I wonder what a blend of it and the granite would yield.



#9 jrgpots

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Posted 19 April 2014 - 06:39 PM

I have one glaze recipe I could replace EPK with this clay to get tenmoku. I'll try it. Thanks

Jed





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