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I would maybe treat this clay as red earthenware, which is how it seems  to be acting.  The aldershot clay deposit near Burlington, Ontario produces a similarly firing dark brown brick and it has a pce of about 7-9.

I agree with Callie that the test cylinder looks a little slumped and may have begun to bloat.  Cone 2-3 might be a good test for next time

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Unfortunately, I have not been able to edit my picture size-yet. Edit button does not come up when I double tap pic.

This piece is just slightly larger than a shot glass: 1/8lb. of clay perhaps. Spent perhaps 30 seconds forming it and then into the hot sun it went. All I know at this point is: WOPL = 29.  Nearly zero plasticity. All material passed through 100 mesh screen,  and less than half through a 200 mesh.  From that:  alumina 30%, silica  45%, iron 12%, potash  5-6%, titanium 3%. All guesses of course, but comparing the WOPL, color, and mesh sizes to my extensive clay database: close.  Will do more formal testing once I figure out if it produces the color and effects I want. Threw away a couple thousand test bars few months back, so pardon my refusal to make more at this point.

Nerd

Edit: I am wondering if this is a chlorite group/ clay.  2:1:1 with double tetrahydra inner layers: iron fe2 / fe3.  This is close enough to the Arkansas border, where chamosite deposits are common. If that holds true, then iron levels can be over 20%. 

Edited by glazenerd
Information added.

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Chlorite can definitely be a component of a red brick clay.  How much, I'm not sure.  Secondary clays are always a mishmash of whatever and can be variable.  Government pubs can be a good source.   "Clay and Shale resources of Ontario" is where I get my info on local clays.  I tried searching for Missouri publications to help get you on your way, but the only one I could find was from 1896--Missouri Geological Survey's Volume XI "Clay Deposits"  by Herbert Alan Wheeler (I think he's the author, but not sure).  Sadly its information is quite crude and the kinds of clay minerals aren't in it.  Maybe there's a  new edition out from at earliest the 1970s?

I would venture a guess that the iron content is closer to 8-9% at the very extreme.   Which is the max listed in the above book regarding brick clays.  Based on colour, 5-7% is my guess.  Beyond 10% I'm not sure it would be terribly workable, maybe even thixotropic?  If it is 20% it would be more useful as a pigment (or iron ore, if you go for that kind of thing).

I'm sorry to hear you won't be doing any more firing tests at present.  If you're willing, maybe test for brittleness destructively and then have a look at the cross-section for bubbles and signs of bloat.  Your microscope would be instructive here.  

My guess is that it would be a good cone 8-10 single fire glaze base with a little more flux and silica.  Maybe even a tenmoku-kaki.  

This kind of thing is what I love abouy ceramics, the joy of a new material to play with. :)

Edited by Tyler Miller
changed a verb and swapped a sentence

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Tyler: decided to mix an 04 frit ware body, using 25% brick pit clay.

25% high iron local brick pit clay

25% OM4

30% frit 3110

15% A75  silica

5% (IP) plasticizer.              And the result with low expansion clear glaze 1960F peak / 5 min hold 

good call Tyler.   Have a C3 and several C6 variations coming up shortly.

image.jpg.31e84552de4849cada59be6675fa62ce.jpg

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Got my lab analysis back late yesterday. Bought the dirtiest bag of ball clay I could find: 520PPM of sulfur and 0.99% carbon by weight. Already had an analysis on brick pit clay, iron, carbon, and sulfur content.  My theory at this point:

X percent of sulfur will produce bloating.    (already dialed in to some degree)

Y percent of carbon and iron will exacerbate the problem.

Z percent of carbon & sulfur will produce carbon coring.  ( This should be significantly higher than the bloating level).

** The iron in most clay bodies comes from FeS ( iron sulfide), also known as pyrite.  So increasing levels of iron should correspond with increased incidents of bloating and coring.

Not so sure that is solely carbon that causes coring: at 0.99% carbon, does not strike me as enough carbon content to completely discolor the entire body.

** some of the last testing I will do on stoneware before I move on to earthenware/ terra cotta.  (Done with porcelain.)

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Guest JBaymore
2 hours ago, glazenerd said:

  So increasing levels of iron should correspond with increased incidents of bloating and coring.

Not so sure that is solely carbon that causes coring: at 0.99% carbon, does not strike me as enough carbon content to completely discolor the entire body.

The issue with higher iron content matches my experiences.

Most situations with carbon core-ing involves reduction firing (when the body is open and porous).... so CO and particulate C  might be considered as factors.

best,

........................john

 

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John:

Decided to change my testing protocol, which includes using porcelain for the test body in lieu of stoneware. Grolleg to be exact, this way I can monitor more precisely the iron, sulfur, and carbon content. Early results in my gallery under USB pics.

image.png.64c2a97b1dfb0c82b74bc2a7408a7b35.png

Nerd

Info added:   Carbon 198 PPM  / Sulfur 936 PPM  in this sample.

Edited by glazenerd
tech info added

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For additional info:

Retention of Sulfates by Fired Clay...W.E Brownell (Alfred U) 

April 1960. Journal of the American Ceramic Society"

Abstract- Brownell wrote: " sulfate is retained in a fired clay product as absorbed sulfur trioxide and sulfate salts."

------------------

Calcium and Sulfate distribution in Fired Clay

by Gredmair, Banks, and Pearee.     University of South Hampton

Abstract: " clay body fired to 1050C: the elements of sulfur and calcium combine ...."  

           " black core by reduced magnetite."

 

for those who like to read boring stuff 

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More interesting info on core-ing.

Black coring in structural clay products.  Brownell June 1957. Journal of the American Society of Ceramics

abstract: " analytical procedures indicated that carbonaceous matter was responsible for the formation of black cores."

*** this is what most modern books on clay state about carbon coring..... But they left out this part.

Brownell continues." But the properties of the core were actually dependent on the state of oxidation of the iron."

*** so burning out carbon according to Brownell is not the answer. The answer is oxidizing the kiln in order to impede the sulfur, iron, calcium from bonding; thereby creating an impenetrable barrier that traps carbons, and also traps off-gassing feldspar (bloating)

not tested it yet.. But I would guess the key temps at 1500-1750F (when sulfur vaporizes). 

Marcia: to answer your direct question- ammonium chloride can be wedged into clay in order to dramatically increase the oxidation level in the interior of the body.

Nerd

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20 hours ago, glazenerd said:

ammonium chloride can be wedged into clay in order to dramatically increase the oxidation level in the interior of the body.

Please no one do this.  It produces ammonia and gaseous hydrochloric acid.  There's also an explosion risk, since NH4Cl reacts pretty energetically with some common soluble salts.  Just, please, no.

I haven't been following this thread lately, but the usual electric kiln provides oxidizing atmosphere enough. 

Edited by Tyler Miller

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20 hours ago, glazenerd said:

 

 

 ... - ammonium chloride can be wedged into clay in order to dramatically increase the oxidation level in the interior of the body.

Nerd

Nerd,

Please elaborate on how ammonium chloride increases the "oxidation level" . 

I agree with Tyler re  ammonium chloride.   

Ammonium chloride is the product of the reaction between Hydrogen Chloride (HCL) and Ammonia (NH3).  The equilibrium favors ammonium chloride (solid and/or liquid) at ambient temperatures.  At higher temperatures and atmospheric pressure the equilibrium favors decomposition to ammonia and hydrogen chloride gases.   The details of the equilibrium can be found in just about any Physical Chemistry Textbook.  The Wikipedia entry NH4Cl  refers to: Wiberg, Egon; Wiberg, Nils (2001). Inorganic Chemistry (illustrated ed.). Academic Press. p. 614. ISBN 0-12-352651-5. for more details] .   

Significant amounts of chlorides in high temperature equipment usually leads to significant corrosion unless the materials of construction for the equipment are carefully selected.  

LT

 

 

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8 minutes ago, glazenerd said:

LT:

Brownell proposed the use of ammonium chloride in his "Retention of sulfates by Fired Clay, 1960. The references to the link is provided above. 

nerd

He also said the benefit was mechanical not chemical, opening the clay up.  Using shredded paper or sawdust would be just as beneficial, without the risk to equipment and lungs.

I would take what Brownell's doing with a grain of salt, since he's working in a context far removed from the studio potter.  He doesn't provide a handbook, or even recommendations but illustrations of the mechanics of problems.  

I'm also not convinced the issues he's addressing are particularly relevant to the studio potter.

Edited by Tyler Miller

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Once again: ammonium chloride is a white crystalline powder that is used in cough medicines, facial masks, and cosmetics. When it is heated, it produces ammonium and hydrogen chloride.  The suggested amounts were along the lines of barium carbonate to prevent scumming: 1/4 to 1/2%. How that got translated into industrial levels mystifies me. I would be far more concerned about the interaction of the sulfur content interacting with other salts which produce sulfuric acid. Which by the way occurs every time you fire a high iron, high sulfur dark or red body stoneware. Your pitted and corroded stainless steel jacket is evidence of that reaction.

this reminds me of the calcium borate thread I started in dec. 2015 when I arrived. There was a great alarm over my use of Imsil A-25 silica. Imsil has exposesure limits under 0.025 mg./8hr.: which is the same as any 325 mesh silica. Somehow my assertion of it being an agglomerate material was over looked.

here is a recipe for standard red brick (cone 04)

50% silica , 25% Hawthorne Bond, 25% a Red Art

and here is a recipe for (cone 04) red body 

50% Red Art, 15% Hawthorne Bond, 25% OM4, 5% silica! and 10% talc. ( from Alfred U)

Red Art,  Gold Art, Hawthorne Bond, Greenstripe, Banta, Newman Red, and many ball clays were/ and are used to make brick, long before they were used in stoneware. What we call fireclay is actually brick clay. Pottery consumes less than 3% of mined clay! it is not mined for us specifically: we just adapted it for our use. Stoneware is just a modified brick recipe with different particle size distribution and slightly higher flux levels. Most brick have between 2.25 to 2.50 molar flux levels, while stoneware runs from 2.75 to 3.10.  So yes, Mr. Brownell studies are most relative to our use.

Or, if you prefer to look up the two studies done in Germany, another in Switzerland, a few others specifically done on clay with the same basic conclusions: be my guest. However, sounding the alarm on possible reactions is not necessarily a bad thing either. Personally, I would rate it on the order of manganese fuming. Yet, everyone has to exercise their own sense of caution.

 

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Tom, believe it or not, I am trying to help you.  I have some chem experience and some ceramic experience and I know how to research because I've been to grad school..  

In Brownell's 1957 article (the one I have  immediate access to)  he's clearly saying he's using more than levels for descumming though.  He literally says the product is not chemically beneficial but mechanically, which means lots.

 Leaving that aside, however,  I wouldn't advise anyone to use barium carb to prevent scumming in a studio pottery environment, either, because there are dangers inherent in using  and storing that product. 

I don't think it's wise to use ammonium chloride in bodies, for similar reasons.

1) because of the ammonia /HCl production 2) because it can react vigorously with salts commonly present in clays with decomposing organic matter.  Which will probably not cause a problem, except likely damaging some pots.  As for the corrosive aspect, pure HCl is a lot worse than sulphur dioxide.  Salt firing is more destructive than soda firing because of the chlorides.  And someone on here was using fluoride as a flux and that was very deatructive indeed.

And yes, ammonium chloride is used on an industrial scale as a food flavouring agent, among other things, but that doesn't make it safe while heated or in the presence of salts that can be in a clay body (especially earthenware).  I won't mention what they are because the combos are used to make high explosives like the ones used in the Oklahoma city bombing.  Adding NH4Cl likely won't blow up your kiln, but it may kill a load of pots.

Tom, not long ago you were messing with cadmium salts in your crystalline glazes and quite frankly that put a horrid pit in my stomach. This worries me too.

You're a good guy and I want to see you and your equipment in good working order.  I know I'm a pain in your rear but I really do mean well. If I'm honest, I worry that learning about stuff like cation exchange capacity (a measure of soil fertility) and Brownell's works on efflorescence are keeping you from being the best ceramist you can be. I want you to succeed, I want you to be an expert.  Really, I promise!

Edited by Tyler Miller

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Tyler:

What you call being " a pain", I call passion. 

Passion keeps you making pots for 50 years.

Passion lands your work in the Smithsonian.

Passion  keeps you working on perfecting a glaze, even after a year of failures.

Passion keeps you throwing, even though you cannot keep it centered.

Passion takes you to japan, to study under the Masters.

Passion  gives you the patience to spend 3 hours detailing a single cup.

Problems with passion only arise when our passions are interjected into the arena that others are passionate about. I just happen to be passionate about clay chemistry: which is foreign to most.

When I crossed the 60 mark I stopped measuring success in terms of achievement, and started  measuring it in contentment.

 

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On 11/4/2017 at 7:14 PM, glazenerd said:

Marcia: to answer your direct question- ammonium chloride can be wedged into clay in order to dramatically increase the oxidation level in the interior of the body.

11 hours ago, glazenerd said:

The suggested amounts were along the lines of barium carbonate to prevent scumming: 1/4 to 1/2%. How that got translated into industrial levels mystifies me. 

Perhaps because you didn't provide the suggested amounts at first? Also, when wedging a dry material into moist clay, there really isn't a way to measure it by percentages. 

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11 hours ago, glazenerd said:

Red Art,  Gold Art, Hawthorne Bond, Greenstripe, Banta, Newman Red, and many ball clays were/ and are used to make brick, long before they were used in stoneware. What we call fireclay is actually brick clay. Pottery consumes less than 3% of mined clay! it is not mined for us specifically: we just adapted it for our use. Stoneware is just a modified brick recipe with different particle size distribution and slightly higher flux levels. Most brick have between 2.25 to 2.50 molar flux levels, while stoneware runs from 2.75 to 3.10.  So yes, Mr. Brownell studies are most relative to our use.

I don't yet see how studies on brickmaking are relevant to studio pottery. "Relative to our use" might mean something to a clay chemist, but Tyler's comment was specifically about Brownell and studio pottery. 

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Mea:

brick recipes and stoneware are nearly identical in molar %.  My study of bloating and coring centers more on formula limits when formulating high iron clay bodies to prevent each. However, the daily relevance to potters is how to deal with these issues when they do occur. I have not drawn any conclusions yet, just looking at this point. I do however suspect the answer does not lie solely in burning out carbons. There were studies done in Germany, Switzerland, and others in the U.K. Specifically on clay bodies with nearly the same results.

The more curious part of  I have found was the extensive studies done on clay from 1930-1970's, and then they dropped off except those done for industrial ceramics. Which tells me when clay switched from the studio potter to mass production: the interest changed from clay to glaze.i will make a prediction however: over the next few years clay issues will out pace glaze issues. Potters will discover that many of the pin- hole, grazing, and other defects were not caused by the glaze, but rather the clay.

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Interesting stuff, glazenerd.

But specifically, you took a suggestion from a brickmaking study and offered it to a studio potter. It might very well work, given the proper examination of process and amounts. This proper examination has not been done in a studio setting. But you presented it as a solution, rather than an idea. This is why us studio potters are saying "where's the relevance?" 

Information is important, but context is important too. As Tyler pointed out, the information without the context could have resulted in something dangerous. 

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12 hours ago, glazenerd said:

Pottery consumes less than 3% of mined clay! it is not mined for us specifically: we just adapted it for our use.

Not to split hairs but there is a company in Canada that does just that and has been since 1962 https://www.plainsmanclays.com/index.php?menupath=18

Yes, I realize this is an exception but I'm not too keen on blanket statements.

 

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Glazenerd, saying "my theory at this point" does not automatically apply three comments later. Your response to Tyler was very defensive. If you were still being theoretical, why be defensive? Scientists are not supposed to feel attached to theories. They are meant to be questioned and poked at. 

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Glazenerd,

As much as I don't understand the chemistry behind any of this, and do not deal with clay other than out of the box and into the pot, I do understand discussion, theoretical problems, and research. I also understand the problems with materials if one does not have the full knowledge at hand when mixing materials. I also understand that things we thought worked and were safe years ago, turned out to be harmful as we understood more about them.

All of that said, I believe it is time to ratchet back the conversation to a less accusatory/defensive tone and approach this as a problem with a number of colleagues counterpointing your work. Is this not why we post here? To get answers, to solve others problems, and move forward to better understanding of things Ceramic? That is what I believe. I have read the posts here. . . very carefully, I have seen nothing but support, and concern. There are no snipes, no lies, and no untruths being posted in a negative manner to spite or snipe at you. In the long run, go with the flow, and don't bite the hand extended to support you.

 

best,

Pres 

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Guest JBaymore
13 hours ago, glazenerd said:

 Potters will discover that many of the pin- hole, grazing, and other defects were not caused by the glaze, but rather the clay.

Tom,

Because you are a bit new to the ceramics field (speaking here from about 50 years in it when defining that idea of "new" :))  there are likely "pieces of the puzzle" that have been looked into a bit and some thoughts have been expressed on them in the past that you might not have been privy to.  The ceramics field is SO vast, there is no once central place to go for all of it,  and there are so many details that it is nigh on to impossible to keep up with all of it. 

The idea that pinholes are mainly caused by clay (and the firing of clay) issues  has been pretty well discussed by a lot of the "tech weenies" in the studio ceramics community, including a guy you know a bit...... Ron Roy.  If I am remembering correctly this was a topic of discussion when Ron, Paul Lewing, and I did a presentation together at NCECA a long time ago called "Beyond Alchemy". Pete Pinnel has talked about it a lot.  Ron and John in presentations they have done.  John Britt.  Many others.

As Mea and Pres are saying, you are into an area of what might be termed sort of "academic research".  Within that context, the thing that makes such research really solid in the end, is the "back and forth" and the challenging of ideas and assumptions until there is a solid pile of evidence that supports whatever contentions are being postulated about something.  And also refining the language to explain it succinctly and effectively.  Challenges and "beating the ideas up" by colleagues is a desired aspect of this kind of environment.  It just makes the end product more robust. 

best,

.......................john

 

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