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Sas Clay Formulation / Wopl / Plasticity / Green Strength

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
 

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#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

Firing Clay according to Color.

 

White Porcelain:  being white in color automatically concludes that much purer grades of materials where used in making this body. Grolleg, NZ Kaolin, and Super Standard kaolin have very low rates of impurities and virtually no carbon deposits. Sodium feldspars and standard silica also have little impurities, and contain no carbons.  Following the usual bisq and glaze firing schedules should work for this body. Test for absorption and raise peak glaze fire by ½ cone increments if absorption is more than 1%. Note: due to the composition of these bodies, the COE values are usually significant higher than standard porcelains.

 

White Stoneware:  like white porcelain, this type of body usually consists of cleaner clay varieties.  However, all fire and ball clay/s have some level of impurities and some level of carbons in them.  Part of the attraction of stoneware is the color/s produced by the presence of iron, magnesium, and titanium. The higher the levels of these three elements go: the deeper the toasty color of stoneware becomes.  Following standard bisq and glaze firings should  work for this body. Note: stoneware has a blend of coarse particle fire clay that must have a relational portion of sub-micron ball clay to minimize porosity. After absorption testing, raise peak temperature by ½ cone until absorption is below 2%

.

Grey Porcelain:  this body color indicates a utility blend. It is designed to be inexpensive, plastic, and used in the widest range of applications.  Grey color indicates carbon, which are usually dealt with in the bisq fire.  If pin holes show in the glaze firing;  then adjust your bisq fire temperature up by 50-60F with a short 10-20 minute hold to help burn off carbons.  Grey Stoneware: can be a particular problem because of bloating. As carbons burn off, they create an impermeable barrier that traps off gassing feldspars that can be small to large in size. As bloating area increases: this also indicates higher levels of carbons. If bloating continues after several bisq or glaze temperature adjustments: it may be wiser to discontinue use. Bodies using higher carbon ball clays are tricky; if accompanying feldspar levels are too high: the problem is nearly impossible to remedy with firing schedules.

 

Brown/Dark Stoneware: brown/dark clay is most always indicative of high iron levels. With iron, comes higher magnesium and titanium levels: these two elements almost always proportionately increase as iron increases.  The combination of them creates that warm toasty brown that potters know and love. The problem then becomes, large particle feldspar minerals are always very common in these types of ball clay. Unlike finely ground feldspar in your glaze; these are coarse and hidden in the interior of the clay body where heat takes the longest to reach. Consequently, brown/dark stoneware is the most susceptible to pin holes and blistering because large particle feldspar in the body takes much longer to off-gas. This body is the one that requires a change in glaze firing schedules most often to resolve off-gassing issues. Rarely seen in cone 10 schedules, and often seen in cone 6 schedules.

 

The Remedy given is usually a higher bisq fire which will not work because are not dealing with carbons; but rather feldspar particles. At bisq temps, there is simply not enough heat to fully resolve feldspar off-gassing issues. At 2190F, normally all feldspar are at the end of their useful cycle; unless they are large and inside a clay body. Some studies suggest it takes heat twice as long to penetrate a clay body as it does the glaze coating the surface.  This body then requires a higher peak temp at cone 6: 2230F. It also requires a short to extended hold pending the kiln size.

 

Of course if the goal is not vitrification; then trying to achieve optimum firing results really does not matter. However, some blended fixes may still be required to resolve bloating and pin hole issues. Primarily, higher bisq temps are utilized to burn off excess carbons, and higher glaze temps are used to remedy pin hole and crater issues. Bloating can be fixed or minimized mostly; but often cannot be resolved because of poor formulation of the body.

 

50 35m
 
Large particle (20 mesh) feldspar mineral inside a stoneware body. 200x
 
Nerd


#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



#54 glazenerd

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Posted 31 March 2017 - 11:02 PM

The Nerd Plasticity Test:

 

There is a lot of discussion about plasticity: what it means and how it is applied. The only way a potter can gauge plasticity is by throwing the clay on the wheel; and even that is subjective. If it moves around easily on the wheel then it is plastic, and if it is stiff then it is termed short. Is there any simple way to determine when a clay is plastic, and when it is not?

 

The first thing you have to do is set a baseline: to have a sense of what real plasticity "feels" like. Dip your thumb and middle finger into vegetable oil and gently rub them together: that slick, non friction, ease of movement is plasticity.

 

To test an individual clay; mix an 1/8th of a teaspoon of dry clay into a 1/2 teaspoon of water: let it set a few minutes to allow for some water absorption. Now dip your thumb and middle finger into it: and rub them gently together. Is it course, gritty, can you easily feel your thumb and finger? That course, gritty, friction you feel is non-plastic clay.

 

Now repeat the test with bentonite: mix it the exact same way- 1/8th teaspoon of bentonite with 1/2 teaspoon of water. Let it set a few minutes to absorb: now dip your thumb and finger and gently rub them together. Feel the difference? Feels slick, almost like the vegetable oil you started out with: that is plasticity. The chemistry definition of plasticity is negative cation exchange between particles that causes them to repel the adjoining particle: potters refer to it as : "sliding past each other." The slicker, slimier the clay feels between your fingers: the more plastic it is. So you can test all your individual clays this way, and you will have some measurable sense of how plastic they are.

 

You can also take a small sample of the clay body you use and thin it down with water until it is a heavy cream viscosity: like the vegetable oil. Do the same thumb and finger test; rub gently: how slick is it? Is there a sense of texture, feel course: then it has low plasticity. Do your fingers slide easily, does it feel slimy: then it has high plasticity.

 

Yes it is subjective; however you are the one doing the testing. So your sense of feel is involved in every test: just keep the water levels and viscosity as close as possible. After doing several different individual clays, thinned clay bodies: how do they feel against bentonite or the oil?  

Nerd



#55 JBaymore

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Posted 03 April 2017 - 10:35 AM

Nerd.... FYI:  http://ceramicartsda...ody-plasticity/

 

best,

 

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


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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


#56 glazenerd

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Posted 03 April 2017 - 04:37 PM

Ty John

 

Perhaps I will send some research papers to Alfred to help fill in their blanks. They were questioning the role of electrostatic forces in the role of plasticity: it has been studied and verified by over a dozen Phd;s. The reason particle size is attributed to plasticity is because: as the particles get smaller, the presence of alumina drops as well. Perhaps an illustration: 

 

Bentonite, hectorite, and smectite clays typically run between 0.40 down to 0.25 particle size with alumina well under 10%

Ball clays: run  0.50 up to 0.95 particle size, but run 13-21% alumina.

Porcelain is above 1 micron and runs 25-37% alumina.

 

So the association between particle size and plasticity is correct; but it is not the particle size but rather the alumina content that actually produces the plasticity. Cation exchange is directly related to the alumina content ( as noted in all research papers); it is  the alumina that conducts and transfer molecular charges. Just like the aluminum high voltage power lines above ground that carry the current, alumina is the sub micron conduit of electrostatic charges. As the alumina decreases, so does the electrostatic charge: that just happens to coincide with particle sizes: with some exceptions. A negative charge equals plasticity.

 

Modern science has developed many man made polymers that will impart more plasticity to a clay body, than any natural plasticizers. They are used in tooth paste, facial creams, make up, and a host of other products to make them all creamy and dreamy. The article also stated there are no scientific ways to measure plasticity: actually there are several. Although, as will all things clay in pottery it would cost time and money to purchase that equipment and that would add money to a lb. of clay.

 

Nerd



#57 glazenerd

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Posted 12 April 2017 - 10:17 PM

The pottery text books state that plasticity is directly related to the particle size of the clays used to blend the body. While this is actually a true statement: it does not explain the chemistry behind it. As noted above: CEC (cation exchange capability) is the actual chemistry behind plasticity. The ability of clay particles to absorb and transfer an electrostatic charge directly effects plasticity; as well as causing memory in clay. A negative charge produces plasticity and a positive/neutral charge produces memory.

 

So the question then becomes: how does particle size effect the electrostatic charge? After reading numerous research articles about CEC: it turns out that all of them point to the alumina levels in the particle. The alumina level is directly responsible for either a positive and negative electrostatic molecular charge. This makes perfect sense, in the world of large objects (things we can see) it is also alumina (aluminum) that conducts and transfers electricity. Alumina does  the exact same thing on a molecular level between molecules which make up clay particles. It is only when water is added to clay powders, that the electrostatic charges are transferred between particles: the combined total of all the ingredients determine the final equalized molecular charge.

 

As it turns out, the smaller the particle of clay: the smaller the levels of alumina they contain. As the percentage of alumina decreases; the negative cation exchange increases: as the negativity increases, so does plasticity. Transversely, as the particle size increases; so does the alumina levels: as the alumina levels increases: plasticity decreases and memory increases. So there is a direct relationship between particle size and alumina levels; just as there is a direct relationship between alumina levels and electrostatic charges.

 

The smaller the particle; the lower the alumina levels which equals higher plasticity due to negative electrostatic charges.

The larger the particle; the higher the alumina levels: which equals lower plasticity and more memory.

 

Bentones*, which include bentonites, smectities, hectorites, macaloid, and V-gum T *synthesized*  This group can have as little as 1 percent alumina and be as small as 0.25 microns (sub-micron). Even in this group of sub micron particles: as each increases in size from 0.25 up to 0.50 microns: the alumina level increases. Smectites and Hectorites can be as small as 0.25 microns, and have less than 1% alumina: and are also the most plastic of this group. Bentonites run 0.40 up to almost 1 micron: and as the particle size increases: the alumina can reach nearly 20%. The micron size and alumina levels directly effect the plasticity of each classification of bentonite. (sodium, calcium, magnesium, and fluorite).

 

Ball clay is known for it's plasticity, but like bentones are directly effected by alumina levels. Foundry Hills Cream (FHC) is considered highly plastic and often used in clay body formulation for plasticity. It is classified as sub micron, but it has 20% alumina levels. So even in the sub micron class of clays: highly plastic particles @0.25 microns run 1% alumina, and moving up to 0.75 microns can have nearly 20% alumina. OM4 ball clay is nearly one micron, and has higher alumina levels than FHC. So yes particle size does effect plasticity: but it is not the size of the particle, but rather the alumina level. The lack of alumina therefore means the lack of ability to transfer electrostatic charges which results in a negative charge which produces plasticity.

 

Kaolin has the opposite problem: particle size ranges from 1 to 5 microns in general. Like bentones and ball clay, as the particle size increases; so does the alumina levels. Typically kaolin average 37% alumina; which explains it's neutral electrostatic charge. Unlike ball clay which has a negative electrostatic charge that creates plasticity: the higher alumina levels in kaolin cause a positive electrostatic charge which creates memory. As  the alumina level increases in kaolin, so does the memory.  When sodium is used as a flux in porcelain; the memory increases further because sodium has a strong positive electrostatic charge. When potassium is the primary flux, the memory is slightly reduced because potassium has a weaker positive charge. The only remedy for the strong positive electrostatic charge in kaolin (porcelain) is to introduce a sub micron particle that changes the charge to a negative polarity. Macaloid and V-gum are the smallest particles, with the lowest level of alumina: therefore having the strongest negative charges which can change the overall positive polarity of kaolin. The other solution is to use much higher percentages of sub micron ball clay to change the electrostatic properties of kaolin.  

 

So yes the text books have it right: as the particle size decreases, the plasticity increase. It is not the particle size however, it is because as the particle size decreases, so does the alumina levels. The lack of alumina translates to the inability of the particle to transmit a positive electrostatic charge. So when your considering a ball clay for plasticity reasons: look at both the particle size but also the alumina levels. The particles with the lower amount of alumina will have higher plasticity properties. The age old debate about the differences between stoneware and porcelain comes down to alumina levels. While both bodies are indeed clay: it is the alumina levels that make the distinctions between them.

 

Nerd

 

** particle size and alumina levels also play a role in the ability of clay to act as a suspension agent, which I will address later.







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

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