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SAS Formulation stoneware WOPL Plasticity Green Strength particle distribution paxking density

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#41 Dick White

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Posted 26 December 2016 - 12:33 PM

Ok, now you've shifted the battlefield... here come the polymer "clay" crafters who now like to call their medium "cold porcelain."



#42 glazenerd

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Posted 26 December 2016 - 02:06 PM

The real truth is much easier: clay bodies are what the manufacturer tell us they are.

 

Secondly, the only reason mullite formation has become important in the last decades: is because the military is interested. It seems mullite glass is much stronger than borosilicate: hence thinner blast proof armored glass.

 

Lastly, my brain hurts from thinking about it. Perhaps it is time to just to pull my threads down and go back to the age old method of blending clay: throw some crap in a bucket and cook the crap out of it. Apparently clay chemistry is not of any relative importance.at the end of the day. In 2016, I should not be writing a book about clay chemistry, I should be reading one written 100 years ago.

 

Nerd



#43 curt

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Posted 26 December 2016 - 11:52 PM

I think the chemistry is critically important.  So is the array of particle sizes.  True for stoneware, but even more important for porcelain.

 

However, as I said way back at the beginning of the stoneware limits thread, if you don't define what end objective(s) you are trying to achieve by manipulating these variables, then you will never know when you have arrived.

 

My own focus at the moment is on developing FUNCTIONAL clay bodies from native materials.  Since all my native materials are full of iron, you know immediately I am not working on porcelain.  No, I am after a general purpose Cone 10 stoneware body that looks good in both oxidation and reduction.

 

As I said, perhaps the primary way I define "functional" at this point is porosity.  For me to label a clay body functional it must have water absorption under 2%, and ideally closer to 1%.  This is mainly an issue of flux amounts and silica, but also of particle size.  If particle size is too large, even unreasonable amounts of flux may not work to achieve my porosity target. So all the stuff we have been discussing with regard to chemistry must come to bear, along with particle size issues. 

 

And the ideal firing temperature and hold times to produce this ideal porosity given the flux and particle size packages will need to be identified. Or otherwise, the mix will need to be tweaked to make Cone 10 with a 30 minute hold (our standard community firing profile) be the "right" amount of heatwork.

 

And this body has to be good for throwing and handbuilding.  So it must be able to be wedged, bent and otherwise worked without falling apart, which in turn requires a carefully selected distribution of plastic and non-plastic materials of different particle sizes. 

 

Oh, and it cant have TOO much iron, don't want it too dark.

 

Oh, and I don't want it to look grey (magnesium!).

 

And...and....

 

Anywhoooo...you can see that all these requirements have specific implications for both chemistry and physical attributes of the raw materials.   In the end I don't think it is asking too much.  It can be done.  It is tricky but I am getting closer.  Just getting into the right porosity zone has taken more than two years, and many many many tests.

 

So it should be clear that not just any mix of stuff will do.  My porosity objective and related wish list is not going to happen by accident, or by just borrowing somebody else's 3rd-generation, hand-me-down recipe from who knows where originally developed for who knows what purpose.

 

This stuff matters.  Not very many people are out there doing it.  And when they get it right they probably ought to start a clay business....



#44 JBaymore

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Posted 27 December 2016 - 09:03 AM

  Not very many people are out there doing it.  And when they get it right they probably ought to start a clay business....

 

Very true.

 

When I started in clay in the late 60's, just about every full time pro had his/her own clay body recipe.  If they were not mixing it themselves in something like a Bluebird Batch Mixer or a reclaimed commercial dough mixer, and pugging in a Walker pugmill or just wedging the crap out of it by hand... then they had the recipe being mixed in bulk by one of the few ceramics suppliers.

 

Fast forward to now... and so many folks just use the stuff that the suppliers sell... and have no idea or any control of what is actually IN the clay body that they use.  Myself included for a couple of the bodies that I use,..... but I know the additions that I put into them to change the look.  However some other bodies I use are of my own formulation.

 

The health and safety concept of "transference of risks" is of course a factor...and likely a good one for most folks.  Move that operation to someplace that has the equipment to do it safely and reduce your own exposure to the dust factor and the somewhat dangerous equipment operation.

 

best,

 

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


John Baymore
Adjunct Professor of Ceramics; New Hampshire Insitute of Art

Former Guest Professor, Wuxi Institute of Arts and Science, Yixing, China

Former President and Past President; Potters Council
 

http://www.JohnBaymore.com

http://www.nhia.edu/...ty/john-baymore


#45 glazenerd

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Posted 27 December 2016 - 06:53 PM

I know more about clay, than I had planned on knowing. This whole process started because I had to figure out a porcelain body that would with-stand crystalline glaze, and a body chemistry that did not hinder development. I threw in dirty porcelain for fun.

 

Tom



#46 glazenerd

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Posted 28 December 2016 - 10:49 PM

Was reading the "Atterberg Limits" again today. Those wondering where our definitions for plasticity, short-long, slip viscosity, and water limits came from.

 

Nerd

 

Was happy to see SAS mentioned in relation to plasticity.



#47 Mark C.

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Posted 28 December 2016 - 11:40 PM

 I used to make clay back when I was not using so much-it became just to hard on the body even at a younger age. It was not cost/and time efficient as well.

I choose to spend my time making pots instead of clay.

The upside about making is the total control of your clay body .


Mark Cortright
www.liscomhillpottery.com

#48 glazenerd

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Posted 29 December 2016 - 07:40 AM

Mark:

 

I am awaiting the publication of my work: the idea of selling five copies keeps me motivated. Although the knowledge of insomniacs reading my thread late at night and drifting off to sleep soon after, does bring some consolation. I am just a nerd; what can I say?

 

Nerd



#49 docweathers

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Posted 16 February 2017 - 01:03 PM

Tom,
That is quite impressive, both your series of posts and your proposed article. I cut and pasted it into one big wordprocessor document. You should have been a lab chemist. They love doing that kind of stuff.

 

When I was an  administrator for a large mental health research project at the University of South Florida, I developed a way of dealing with conflict in the very conflict prone organization.

 

I was In a position  that many people envied and thus was prone to attack on whatever I said, just from jealousy. When this happened I would think for a moment whether anything substantively worth fighting for was at stake or was the battle just over who was right. It was only an ego battle over being right I would typically just look at them and not even answer. I figured that I had offered what insight I could and if they did not find it useful that was okay. If there was something substantive to be gained in the battle, I would argue as hard as anybody else. 

 

As Nietzsche said "that which does  not kill, you makes you stronger"


Larry

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#50 glazenerd

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Posted 16 February 2017 - 10:31 PM

Doc:

 

Ty for the vote of confidence. I would have enjoyed being a lab chemist; you are right about that. I see it as a jig saw puzzle that just needs the pieces put together in the right order. The chemistry side of clay is not of much interest for most; the results that comes from it is. If I posted a clay recipe that was plastic, could be thrown 30" tall with 1/8" walls, and cost 0.25¢ a lb: my inbox would be full. The bottom line is I do enjoy exploring the boundaries; and this summer I will be incorporating some elements that are far outside the norm of our industry. Many interesting chemicals and additives out there used by the technology industry; that are not used in ours. Additive A has many forms, and comes in very specific formulations. Imagine a tablespoon of additive causing more plasticity than a pound of V-Gum. Perhaps a 1/4 of a cup of a molecular inhibitor that gives clay the feel of being six months old, even though you just mixed it. I see many avenues of exploration that have not been traveled before..... we shall see...it depends.

 

Nerd



#51 docweathers

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Posted 17 February 2017 - 10:56 AM

Hi Tom
Re: your email It is easy to support a good idea.

 

I'm interested in what you come up with on additive A. Some time ago I posted a message  on the board asking if anyone had tried it. Of course, nobody had but many posted irrelevant comments.

 

I too like to solve the problems, but more from the mechanical end than the chemical end. That  is a reason that I call myself the gizmo guy. Also being a welder helps me make strange gizmos to make pottery easier.


Larry

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#52 glazenerd

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Posted 07 March 2017 - 10:32 PM

saved for future post.



#53 glazenerd

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Posted 09 March 2017 - 12:21 AM

For those interested in the chemistry of clay:

 

https://en.wikipedia...change_capacity

CEC (cation exchange capacity) is the exact mechanism behind clay plasticity. It is common knowledge among clay junkies that the particle charge determines plasticity. A negative charge means the particles are repelling each other: which is commonly expressed in the clay arts as; "sliding by each other." A neutral or positive charge then means clay particles are attracted to each other: which is the basis of memory. Mechanical forces (throwing/rolling) distorts the grain boundaries formed by a positive charge: but the positive charge attracts those distorted particles: drawing them back into a positively charged particle alignment. 

 

Towards the bottom of the article posted is the "standard values" for clays and soils (CEC). It is measuring the properties of clay types to readily exchange cations in the presence of water.

 

Kaolinite 3–15 Halloysite 2H2O 5–10 Halloysite 4H2O 40–50 Montmorillonite-group 70–100 Illite 10–40 Vermiculite 100–150

As you can see: kaolin and halloysite (new zealand kaolin) have very low CEC values, while montmorillonite (bentonite) and vermiculite have very high cation exchange capacities. (CEC) Vermiculite is classified as a 2:1 clay structure: which is the same structure classification given to ball clay. In simple terms: a 2:1 clay structure has two inner platelet structures, and one exterior platelet structure. Kaolin is a 1;1 structure: meaning is only has a surface platelet, with no interior structures. This is the important distinction between porcelain and stoneware: because the clay variety dictates how the formulated body reacts/acts. A 1:1 clay structure (kaolin) can only absorb water onto its exterior platelet, while a 2:1 clay structure can absorb water onto the face of the platelet, but also into its interior structure. This particle structure then effects the clay type ability to A. carry its own electrostatic charge, or B. conduct/transmit a electrostatic charge.

 

Kaolin has a 1:1 particle structure: so it can only absorb water onto the face of the platelet. Secondly, it has a neutral electrostatic charge (polarity), so that neutral charge means it has no ability to influence or transmit that charge to adjacent particles or other elements mixed with it. This property means kaolin will therefore be readily influenced by whatever electrostatic charges of the materials mixed with it: and that charge will only be carried onto the face of the platelet. Sodium and potassium both have strong positive electrostatic positive charges: sodium moreso than potassium. So when flux is added; the positive charge of those fluxes are carried on the platelets of the kaolin. A positive charge then A. greatly reduces plasticity because a negative charge is required for the particles to slide past each other. B. increases memory properties because the positive charge attracts the adjoining particles when mechanical forces separate or distort them.

 

Ball clay has a 2:1 particle structure; which can absorb water onto its exterior face, but also into it secondary platelet structures. Ball clay has a naturally occurring negative charge: which is why ball clay is so plastic. The negative electrostatic polarity resides both on its platelet face, but also inside its interior structures. In this case, when positively charged fluxes are added: while the positive charge effects the platelet face: the interior structure retains its negative charge. The negative charge is the over-riding polarity in the clay body (stoneware) and its plasticity is preserved. In addition, the negative charge is the over-riding influence in the body: effectively eliminating the memory caused by a positively charged clay body.

 

The 1:1 structure of kaolin limits absorption of water; being bond to its platelet face only. This also determines it's drying time, because the platelet surface shed water at an accelerated rate: causing a much more rapid drying time. Ball clay being a 2:1 clay structure absorbs water onto its platelet face and into the secondary inner structures. This results in a much longer drying time because the water absorbed into the interior secondary structure takes much longer to dry. The absorption of water into its secondary structure is what also determines how soft or firm a stoneware body feels to throw pending on the ball clay type, the percentages used, and the amount of fire clay added. What feels like :mass", is actually the additional water absorbed into the interior structures.

 

The other key in differentiating kaolin and ball clay is alumina levels. Kaolin have much higher percentages of alumina compared to ball clay. While it is widely accepted that kaolin and ball clay are both aluminosilicates separated only by the amount of carbons: that is not a true assessment. Alumina is a metal oxide that is solely responsible for the lack of a negative charge in kaolin. Alumina typically has a much higher positive charge (up to 3x) that of silica: the other major component in clay. The lack of alumina in ball clay is what effects its valance polarity: being negatively charged giving its plasticity. The  higher levels of alumina in kaolin is what causes it to have a neutral electrostatic charge, causing it to have much less plasticity; and much more memory. While kaolin and ball are both clays: it is the alumina levels that makes the distinguishable differences between them.

 

Stoneware being mainly comprised of low alumina ball and fire clay does not require additions of negatively charged ball clay or polymers to produce its plasticity. Porcelain being primarily kaolin, requires negatively charged ball clay or polymers to create its plasticity. In addition, the structure of the clay also determines how much water the clay particles will hold: which also determines how fast it will dry.

 

Nerd







Also tagged with one or more of these keywords: SAS Formulation, stoneware, WOPL, Plasticity, Green Strength, particle distribution, paxking density

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