Terra Cotta: My musings on...and resulting actions with.

HorseloverFat

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I have been experimenting with terra cotta lately. I have performed numerous tests using varying dry/wet filtration methods relying mostly on particulate sizes and impurity concentrations of clay from different areas.
 

HorseloverFat

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My goal was to first find a clearly superior composition “right off the bat” merely by geographic selection (After appropriate test batches and runs were made ((up until after my preliminary oven set/dry prior to “firing”)))
This was achieved after several months of gloriously earthy expeditions and semi-rigorous note-taking. Sooo.. Check!
 

HorseloverFat

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I am now currently in the process of using material collected from the prime location (so far) and subjecting it to a series if similar tests as laid out before, except “further” in the refinement process for the purpose of understanding this “earth”’s parameters alllllllll the way to the corner before considering temper tests.
 

HorseloverFat

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(HAVE to post it this way :) )


That being said, I basically do not know anything, and am very early in my process. :)

My first two test pieces were “fired” today.....

The workmanship it quite rubbish, I understand. These are “control groups”... just thought I’d share (just using this thread for my projects “like this” ;)
 

HorseloverFat

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Terracottatest.1 - Two Creeks clay - 1/4” (coarse!) water-filtered - 36hr “proof time” - 180 degree set/dry - pit fired on clay tile with assorted driftwood - clear coated (frosted glass) -

C0D723B0-0C6A-4BEE-96DD-142B7486162E.jpeg
 

sorce

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Terracottatest. 3. “Specifics irrelevant”

View attachment 305993

....and we learn.

Were they completely dry when you fired em?
The best test is to weigh them, and when they don't lose weight after a couple days, you're good.

Of course, pit fires can heat them up too fast. A handheld IR therm can help you keep them hovering around 200 for a while, before picking up the board they are on, and sliding it into the fire further.

I've been able to "pitfire" the local without breaking it, so you'll get it.

My 102 YO Potter friend said she was able to take clay from the bottom of a lake, and fire it all the way to cone 6, this may have been Michigan, but it could have been Wisconsin. Of course, that was so long ago the composition could've changed! Lol!

We used to visit a lake in SoWi that was clay underfoot, by Jellystone Park?
So even if it was Mi..it could be the same deposit I reckon.

This gal Ginger is active and I've messaged her on Glazy, she has some good knowledge of Wisco materials. This is a cone 10 glaze. Which means, these materials can also increase the temp and change the composition of your tests if needed.Capture+_2020-05-30-06-56-06.png

Since the "window of vitreous" with earthenware is so small, between solid and melted, you can add "openers", some kind of organics, to make it so porous it won't crack in the freeze.

So far, 1850F doesn't melt our local.

Thanks for sharing!

Sorce
 

HorseloverFat

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Were they completely dry when you fired em?
The best test is to weigh them, and when they don't lose weight after a couple days, you're good.

Of course, pit fires can heat them up too fast. A handheld IR therm can help you keep them hovering around 200 for a while, before picking up the board they are on, and sliding it into the fire further.

I've been able to "pitfire" the local without breaking it, so you'll get it.

My 102 YO Potter friend said she was able to take clay from the bottom of a lake, and fire it all the way to cone 6, this may have been Michigan, but it could have been Wisconsin. Of course, that was so long ago the composition could've changed! Lol!

We used to visit a lake in SoWi that was clay underfoot, by Jellystone Park?
So even if it was Mi..it could be the same deposit I reckon.

This gal Ginger is active and I've messaged her on Glazy, she has some good knowledge of Wisco materials. This is a cone 10 glaze. Which means, these materials can also increase the temp and change the composition of your tests if needed.View attachment 305995

Since the "window of vitreous" with earthenware is so small, between solid and melted, you can add "openers", some kind of organics, to make it so porous it won't crack in the freeze.

So far, 1850F doesn't melt our local.

Thanks for sharing!

Sorce

Thank you SO much! ...truth be told, I was hoping someone with some knowledge and experience would chime in.

I appreciate it, and will continue on.. experimenting..

(thank you, also, for the temperature and moisture advice.)
 

Leo in N E Illinois

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Question, why reach for "terra cotta" the lowest quality, lowest strength of the various grades of clay / firing combinations? Terra cotta is not as resilient as common brick. I would investigate getting to "stoneware" quality if at all possible.

But not all clay is up to "stoneware".

Not far from my sister's home in southern Illinois there is an old, abandoned kaolin quarry. Has a "nice" swimming hole in the pit. From the walls of the quarry there are bands of snow white, red, and black-ish clay. I always thought if I ever got into making my own pots I would get back there and harvest some clay. But I probably will never get around to making my own pots.
 

HorseloverFat

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Question, why reach for "terra cotta" the lowest quality, lowest strength of the various grades of clay / firing combinations? Terra cotta is not as resilient as common brick. I would investigate getting to "stoneware" quality if at all possible.

But not all clay is up to "stoneware".

Not far from my sister's home in southern Illinois there is an old, abandoned kaolin quarry. Has a "nice" swimming hole in the pit. From the walls of the quarry there are bands of snow white, red, and black-ish clay. I always thought if I ever got into making my own pots I would get back there and harvest some clay. But I probably will never get around to making my own pots.

Great info, Leo. Thank you, as always.

Perhaps my terminology is incorrect, then. The location where I collected had the more orange clay and also strips of reddish black... does the terminology refer to filtration methods and lack of kiln? Or tempering material added?
 

sorce

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kaolin quarry.

🤔 😃

Oh you're making a pot!

I was thinking about how the term "Terra Cotta" insinuates, Roman?, Ancient Greek?, Clay.
There are probably a specific chemical analysis that makes it "Terra Cotta".

Technically, the Cristobalite Crystals of lower temperature clay, is what gives it it"s strength, or lack of, since they are not as long, ahem, and strong, as Mullite Crystals, which only form after certain temperatures can be achieved.
Stoneware.

Those Koalin mines, contain little organic matter, and I believe they might sift, seive, float, or fire out organics before bagging it.

The organics of Any found clay makes it more prone to carbon coring, and may need adjustments, fluxes, etc, to properly both burn out all carbons, and melt correctly.

Of course, firing schedule is paramount to all, the slower the better, control not really achievable in a fire pit.

But helll with not having pitfires!

Though I am on a rebel mission of....

A kiln in every home by 2025!

I'm super de duper itching to find a "local" deposit of "stoneware" clay. That would be soooopreme!

Sconsin!

Have you 2 met yet?

I gotta do Waukee soon! 😷

Sorce
 

HorseloverFat

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So the cristabolite crystals are what primarily compose the ''clay'' part of most hillside/bank clay deposits? Are there other desireable crystals in this comoosition?
 

HorseloverFat

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[as may be signified by deviances in color and texture distictly running through in ''flaky rivers'']
 

HorseloverFat

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Theoretically samples could be analyzed and compared prior to extensive collection....i could do that
 

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