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Calcium Bentonite Vs Sodium Bentonite In Clay Bodies

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Well, I was delayed. 

So if I understand you, you are saying that if you use CALCIUM bentonite in a plastic clay body, at first it will seem short, but if it ages for a few days it will become plastic.  And if a SODIUM bentonite ages for a few days, it will become soft?  My experience is that porcelain (I'm only talking about porcelain because that's the only clay body I've experimented with, well, not entirely) with either sodium or lithium activated calcium bentonite, AND standard Wyoming (sodium) bentonite, AND Hectorite (Hectalite 200 or  Macaloid-a sample from before they sold out to Bentone) will NOT soften or become less workable after aging.  My experience is that it (clay with sodium bentonite or hectorite) becomes MORE workable.   I probably have in the past allowed a sample with calcium bentonite to age, but I just don't remember what happened regarding workability.  I'll sure give that a try.

You are talking about "Ceramic Science for the Potter", about particle size?  I'll look that up later today.  Here's an interesting tidbit.  I use Plastic Vitrox "clay" in my current clay body. 
The word "plastic" is a little of a misnomer.  I also use it to make throwing bats, but it (PV) shrinks, which helps cause the bats to warp a little.  So I calcined 10 pounds of it at cone 05, and it was STILL plastic, such as it is.  And it is pinkish tan/brown!  Also, it seems to "loose" water more easily, and so far it has helped with the warping.  But it still shrinks, just not quite as much.  I think it might have something to do with the shape and/or particle size of the PV, which maybe doesn't change firing to cone 05.  Don't really know what is going on there.

About Neph Sy, YES, I hate it in a clay body, mostly because it becomes so thixotropic when it sits around a while.  I knew it releases soluble material but had no idea it was in the neighborhood of 18%!  It does make sense if the soluble portion migrates and concentrates itself it would outgas more vigorously.

I do not really use Macaloid, but thought it was sodium hectorite.  It is now called Bentone something or other I think, changed owners more than 10 years ago.  I have gone to that area many times, and once went to the office in Newbury Springs and the lab gal gave me samples of stuff.  I do know Hectalite 200  is a natural sodium hectorite with considerable CaCo3 in it, on the order of 20%.  That calcium is not in the clay crystals, it is just a contaminant of calcium carbonate..  Macaloid probably has the same contaminant, but I believe they refine the bleep out of it and get most out.  I would need evidence before I accept that Macaloid/Bentone is a calcium hectorite rather than a sodium hectorite.  Actually, I do not believe I have ever held in my hand a sample I KNEW to be calcium hectorite.  I spoke to an American Colloid salesperson before I wrote that CM article and he said Hectalite 200 was mined in the wilds of Nevada, "Superstition Mountain" I recall, not near Newbury Springs.  They might have mined a lot of it and squirreled it away, maybe in South Dakota or somewhere.  At least then, they were not actively mining it, the salesperson said.  It is a naturally occurring sodium hectorite that they just grind to a powder,  That's the one I use.  I take into consideration the calcium carbonate in the material.

The guy at American Colloid said sodium hectorite was formed in the oceans millions of years ago, and calcium hectorite was formed in fresh water.  Even though they differ in sodium and calcium, they do share the Ii20 and magnesium.  The lithium angle is what got me going on activated bentonite.  I figured if hectorite had lithium in it and it was so "plastic", why not add lithium carb to bentonite and see what happens.  And Lo, when I added it to Bentolite 10-L, calcium bentonite,  it gelled like sodium bentonite.  With bentonite 325 (sodium) it did absolutely nothing.  I thought I had made a momentous discovery until I checked The Google and found out industry had been doing this for 80 years.

I'll look forward to your response when I return.

 

 

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And Furthermore.  Clay scientists, although we may want to think of them as closet potters working as scientists for the money, probably don't know squat about what it takes to make a good throwing clay body.  Hey, it's important to US, but to very few others.

 

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Ceramic Science for the Potter, by W.G. Lawrence 

Chilton  Book Co.1972

Quote

Ions such as Ca+2 or Al+3 increase the plasticity of clay-water systems.

Read chapter six "plasticity", where comparisons are made between sodium and calcium.

Ray:

If I recall correctly you are firing cone six crystalline?  I think your quest for the perfect porcelain body sprung from the same reason as mine: you noticed a difference in crystal development on various commercial bodies. I discovered over the course of years, and hundreds of tests that sodium plays a role in cone six; whereas at cone ten the effect is less dramatic. At cone six, sodium certainly contributes to over- population. Just as I would assume you found lithium content in hectorite conducive to crystal development. I actually ran some porcelain test that included 25% spodumene, which produced grossly over populated cluster and needle crystals.

i think there is a general misconception among pugger owners and plasticity. de-airing removes the air and allows for direct water/ clay contact; thereby creating an immediate level of plasticity. However, cation exchange still has an applicable rate law, that includes a period of time before full plasticity is achieved. So the general thought among pugger owners is to add plasticizers until it reaches their preferred level right out of the pugger. The problem being, rather sodium or calcium: additional plasticity is acquired over the next two- three days. 

Currently I use 2 to 2.5% plasticizing materials with whiting additions. When it first comes out of the pugger, it is very much on the short side and snaps easily. One the second day more plastic, on the third more, and by the fourth fully plastic. Then again, I gauge plasticity by intended use: for throwing I intentionally keep it just slightly short knowing it will absorb water when throwing. If hand building, fully plasticity for ease of forming. For press mold, on the fat side to make detail transfer easier, and less pressure required for pressing into the mold.

if you read through the Atterberg a Limits, it will give you some simple tests for plasticity. One is commonly used: rolling out a strand and wrapping it around your finger. However, potters tend to roll it the same thickness as their wares: which is inaccurate. I have found the amount of water used per 1000 grams of clay a better judge. Currently my porcelain recipes use 18-20% water per 1000 grams: well below the norm. Common to see recipes that have 22-24% water content: which means the water is creating pseudo plasticity, not the clay. Kaolin holds water only on it's surface, it has no inner platelets in which to hold water. ( classified as a 1:1 particle.) which means there is no absorption of water, and only enough water to wet the particles is required.

Stoneware however involves a fair amount of (2:1) clay particles which will absorb and store water. So it is common to see 22-24% water additions in stoneware bodies, softer bodies have higher content than that. Stoneware recipes go all over the place in regards to clay additions: other than most have at least 80% combined clay content. I have found using ball clay with higher CEC values much easier to control plasticity levels. For instance, 15% OM4 is common in stoneware, and my ball clay only requires 10% to achieve the same plasticity. Which also means it absorbs far less water when throwing.

Back to porcelain: a cone six recipe of 50% kaolin, 20% silica, and 30% spar. I prefer a much higher molar percentage of alkali at cone six in order to produce higher glass content: or in application: 0% absorption. Secondly, cation exchange is also PH influenced: meaning the PH of the clay can accelerate or retard isomorphic substitution.  This also plays a role in using much less plasticizing material as commonly seen in recipes. I also use a mixture of kaolin, not just one. My primary kaolin has a median particle size of 0.50 microns, less than half the typical values seen.  I will add larger particle sizes if I know it is going to be wood fired, cone 11-12, or other specific uses are known. I do not buy any of my materials from traditional sources with the exception of Mahavir potash. I use 325 mesh instead of 200 mesh silica. 

Most of the recipes floating around come from the studio potter movement, before commercial clay was available. Some advancements have been made, but very little. In the 1940's into the 70's: porcelain was 50% kaolin, 25% silica! and 25% spar: not much has changed. Stoneware recipes were actually adopted from brick recipes: the earliest recipes nearly duplicate brick. Ougland, Brindley, West, and a few others ran extensive testing on clays from the 50's into the mid 70's. Once clay became a commercial commodity, most of that testing fell by the way side. The only modern testing I read about is for commercial applications. Nano- particles seem to be the focus these days: with vitrification at 800 C. 

Porcelain came to Europe in the 1700's, many attempts were made from the 1880's until the mid 1970's to improve and define it. It is now 2018, and no one has yet to write formula limits, or molecular formulas. Then again when you can buy it for fifty cents a pound, who cares?  So I will close with my usual warning that I have been making for the last two years: clay bodies are and will become the number one problem in pottery. Potters attribute dunting and crazing to clay, but the increasing incidents of pin- holing, craters, blistering, cracking, and accelerated drying and glazing issues are also coming from clay.  Pottery consumes less than 1% of raw clay and materials; so we are not on high quality demand list.

Tom

Edited by glazenerd
Restored post, with additional references.

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Seems we are drifting quickly off topic...  The intention of this thread as set out in the OP was to compare and contrast calcium bentonite to the much more well known sodium bentonite.  Water content, porcelain recipes, workshop methods, nephenline syenite, etc. are all valid topics, but unless they are related to bentonite maybe more productive to discuss these topics in other threads?  Just my take and of course happy for mods to weigh in if they feel I have got it wrong.

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On ‎31‎/‎01‎/‎2018 at 11:30 PM, Sequoia Pottery said:

I have tried as much as 5% calcium bentonite (Bentolite L 10 and one from LMV Nevada), and found it does not help workability/plasticity at all, unless activated with soda ash or Li2CO3.  The green packing property , because of the tiny particle size, might make for a tighter clay body, and you maybe could use far more calcium bentonite than sodium, but I haven’t tried that, above 5%.  I recently ordered a sample of Bentolite H from (KYT?, formerly Southern),  and Millwhite, Brownsville, TX.  8 bucks a sack.  But with the idea of activation, cation exchange.   Sorry for the delay here, but I was just looking for information on bentonite and stumbled on this.  Hope someone finds it.

Hi Ray I have also found that calcium bentonite of this magnitude does not make a noteworthy contribution to workablility, although I am using local calcium bentonite rather than the brands you refer to. 

 

On ‎1‎/‎02‎/‎2018 at 8:18 AM, Sequoia Pottery said:

Regarding which of the bentonites, calcium or sodium, produces a more workable clay body, here's a test.  Make two clay bodies, identical except use 3% calcium bentonite in one and 3% sodium bentonite in the other, with the same weight of finished clay, and the same stiffness.  Say, 30 feldspar, 30 silica, and 40 kaolin, not that this is an ideal clay body, but it will show up the effect of the bentonite.  Make a pot with each.   Dollars to doughnuts the clay body with the sodium bentonite will be far easier to throw and will hold up better to the process. That has certainly been my experience, repeatedly

Yes, this is my experience also in similar practical tests.  And contrary to other suggestions, this difference does not dissipate (or reverse) over time.   My impression is that calcium bentonite added in "traditional" sodium bentonite amounts does not make a noticeable difference to workability.

However, I have found there is a small but noticeable natural improvement in workability of pretty much every clay body I have ever mixed over the first several days, bentonite aside.  So my impression is that it is difficult to differentiate how much of this improvement in workability is due to "natural maturing" of the clay body (will leave aside what that really mean for the moment) vs the actual, specific effect of a bentonite addition.

As I mentioned in the OP, the "activation" of a calcium bentonite via a sodium bath is well travelled ground and seems to be as far as most potters have thought about calcium bentonite, ie, "can I change it to something else please?"   I did not know about the lithium angle so that was interesting.   However, what I tried to communicate in the OP was to see if anyone had been using calcium bentonite WITHOUT altering it, since there is a lot more calcium bentonite than sodium bentonite on the planet.

I think a key problem with calcium bentonites is actually identifying them!  As the discussion with Bryan above illustrated, there is a lot of confusion, including with vendors, on whether people are selling/using calcium or sodium bentonite.   We probably have to get a lot more specific about the actual specifications of the bentonite to get at this as there are a lot of different brands out there.  I think there chemistry is the true differentiator.

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39 minutes ago, curt said:

Seems we are drifting quickly off topic...  

Yes, there is some drift. I can understand how the points made can be related but it can obfuscate the OP's original question. In depth discussions regarding methodology, porcelain history, claybody recipes and their water content while interesting, would be better responded to in their own threads.

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On ‎2‎/‎02‎/‎2018 at 2:14 AM, Sequoia Pottery said:

My experience is that porcelain (I'm only talking about porcelain because that's the only clay body I've experimented with, well, not entirely) with either sodium or lithium activated calcium bentonite, AND standard Wyoming (sodium) bentonite, AND Hectorite (Hectalite 200 or  Macaloid-a sample from before they sold out to Bentone) will NOT soften or become less workable after aging. 

For clarity do you mean that you have sodium activated the Hectalite 200 and Macaloid, or do you mean you used it just as it was received?

I have not used Hectorite or Macaloid, but my experience with sodium bentonite is that it effects on workability do not dissipate over time.    

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Curt:

Most all bentonites sold in the States are 3% sodium and 1% calcium. (highly generalized). L10 I believe is 3% calcium and 1% sodium, which is why I assume it is classified as calcium bentonite. 3% calcium is not enough to get the job done.  Sorry for drifting off into other semi related topics, but the end results of bentonite is plasticity. Lots of studies, charts, and graphs out there studying the clay/water reactions to sodium and calcium. Rather you use sodium or calcium bentonite; you are still dealing with cation exchanges. There are a host of other influences that effect both, and result in the final plasticity of the clay.  I will step out of the topic now, and finish the off topic questions elsewhere. 

Nerd

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Hey, I'm loving this! 

Curt (and all),  I did not make any changes to either Hectalite 200 OR any Wyoming bentonite, but not for lack of trying.  I added small amount of lithium carbonate and additional sodium carbonate, with no changes to the behavior of either.  The only changes that took place was with the two"calcium bentonites" I experimented with, Bentolite 10-L  and a local material mined near Death Valley, California.  Both became dramatically more viscous with additions of 3.5% sodium carbonate OR 2.5% lithium carbonate.  I tried potassium carbonate on all of the above, with no effect at all.  Yes, I also tried calcium bentonite (the two mentioned ) AND sodium bentonite (activated and "natural") with many different clay bodies, including different recipes with  EPK, #6 tile, McNamee, Grolleg, Standard, several samples of kaolin I imported from China, New Zealand Ultra Fine, several ball clays, and some mixtures of these.  Sodium bentonite, either those I "activated" or natural made for a better, more workable clay body.  I would also make a coil about 3/4 inch diameter (2 cm) of the samples check for plasticity.  The "short" clay would crack where bent.

About Lithium carbonate.  These experiments started with me noting that hectorite has lithium oxide in the chemical structure of the clay crystals.  And hectorite is the mother of all gelling bentonite-like substances.  So, I on a lark added some dissolved lithium carbonate into a liquid emulsion of various true bentonites, and this addition to the two calcium bentonites completely transformed them.  So I took to the internet and discovered this phenomenon of  "cation exchange" had been patented in about the 1930's in Germany, and there had been at least one description of using lithium carbonate, quite recently, in a journal in China.  

My observation is that lithium carb makes for a more viscous clay, and improves clay body workability more than sodium carbonate at equal additions to a clay body.  The figures of a 3.5% addition of sodium carbonate and 2,5% lithium carbonate was arrived at by trial and error, based on the degree of viscosity change.  I believe the term is "titrate".  At the point where no more visible change was evident in viscosity, I backed off and used LESS, until I arrived at what I thought was the minimum amount that caused this change in viscosity (gelling).  Kind of subjective.

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Tom (and all),  I routinely do the following test on clay bodies.  (1)  Determine the mixed consistency of a plastic clay body at it's best, not too wet, not too dry, as plastic as it can be. (2) make a test bar, at least 100 grams and weigh it. (3)  Dry it out completely (4) weigh the completely dry sample. 

So the wet plastic sample contains "x" amount of water, plus the later measured dry weight.  Usually, the water is about 20% of the wet plastic weight in my experience, or add 25% water to the dry sample for the "average" plastic clay.  4 parts dry clay body and 1 part water.  About.

I have never systematically looked into what this ratio is with and without various bentonites and clay body recipes.  That would be interesting to know.  

I fire to cone 10, and all the tests in recent years are cone 10.

Edited by Sequoia Pottery
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Curt:  How to tell calcium bentonite from sodium bentonite.  The vendors should tell you that!  They don't.  I read at least one article, from a European clay journal sort of addressing this.  The issue was is it proper to call a "sodium activated calcium bentonite" a "sodium bentonite"?  The answer according to this journal article is yes, it is proper because really all bentonites are essentially the same mineral, and there should be no distinction whether or not this placement of the calcium or sodium is by human artifice or natural.

My guess is that most vendors are not aware of the difference between calcium and sodium bentonites.   If in doubt, I would order a small amount and check it or maybe ask.

I believe the advantage of calcium bentonites is that they tend to be much lower in iron than sodium bentonites, and therefore more suitable for white or light firing clay bodies.

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Curt:  I went back and more carefully read the previous posts.  The idea of adding calcium bentonite to a clay body for "packing" purposes, to make for a better clay body, regardless of any improvement in "plasticity".  Let's try it!  The clay mine I mentioned near Death Valley also mines a mineral called "sepiolite"  it is a magnesium silicate related in some way to talc, and possibly asbestos.  I think.  I experimented with it also, and made a low-fire, cone 05 clay.  Extremely small particle size also.  it does not gell, and I could not get it to gell by any additions.  The cone 05 clay body threw amazingly well at about 30%, I have notes somewhere.  It shrank a lot, however, maybe about 17%?  I made one attempt at a glaze that fit it, soaked it in water, etc, it does not lose its ring, appears quite strong.  It is porous, but don't remember a number, but that could probably be manipulated.

So if that kind of addition seemed to work with sepiolite, why not calcium bentonite?  And there is a lot of calcium bentonite all around the world.  I'm going to try it.  Thank you.

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On ‎1‎/‎02‎/‎2018 at 10:18 PM, glazenerd said:

Ray:

the differences between sodium and calcium bentonites in the USA, are a bit misleading. If you go through the chemistry of each one sold: most have 2-3% sodium! and around 1% calcium. ( highly generalized comment) L10 however has 3% calcium! and 1% sodium: so it gets labeled as a calcium bentonite.  From the studies I have read on calcium verses sodium: values have to be well above these to be effective.

Tom

 

Tom, I think your highly generalized comment is too highly generalized.  I remember looking at a large number of bentonites from all sorts of places about 6 months ago when this thread started up, and found hat Na, Ca, Mg and other levels are all over the map.  My impression then and now is that many "bentonite" products are mislabelled, or at the very least mis-understood from a potters perspective. 

Part of the problem is the traditional view potters have of bentonite as only a plasticizer: it is or it isn't.  However, the whole intention of this thread is to go beyond that traditional approach and look at bentonites as we would any other clay body ingredient, namely chemistry and particle size (along with other attributes).     Seen in this light, every bentonite is effective - in more ways than one!

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Curt:

i would have to agree wholeheartedly with your comment above. Yes, I did highly generalize the Ca/Na content: combined they make up a small % of the chemistry. Factually, all bentonite should be classified as magnesium: most are above 20%. After that, classified as swelling or non- swelling. In relation to clay chemistry: the alumina content would be deciding influence for me; although it would have to be non- swelling. The alumina content reflects plasticity; as the alumina content falls, the plasticity rises. I covered that relationship in the Cation Exchange article: CM 1-18. I would also agree any bentonite could be used as a plasticizer, but effectiveness waivers. One of these years I will finish the " plasticizer" table I have worked on for years. 

In regards to clay chemistry as a suspender: non-swelling should be the only choice. In the States, bentonite tends to be as one general product. Like clay, the cheaper the bentonite. Off topic, but it always makes me chuckle: the primary use of bentonite is drilling mud for oil wells.

side note: most bentonite as I recall run 0.25 microns and under. Been awhile since I have looked at that table section. Like most clay nerds, I have tried 6-8 different varieties. In testing, the relative differences in plasticity were minimal at best. As other posters have  attested: increasing % seems to be the only differing value. 

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On ‎4‎/‎02‎/‎2018 at 8:41 AM, Sequoia Pottery said:

Curt:  How to tell calcium bentonite from sodium bentonite.  The vendors should tell you that!  They don't.  I read at least one article, from a European clay journal sort of addressing this.  The issue was is it proper to call a "sodium activated calcium bentonite" a "sodium bentonite"?  The answer according to this journal article is yes, it is proper because really all bentonites are essentially the same mineral, and there should be no distinction whether or not this placement of the calcium or sodium is by human artifice or natural.

My guess is that most vendors are not aware of the difference between calcium and sodium bentonites.   If in doubt, I would order a small amount and check it or maybe ask.

I believe the advantage of calcium bentonites is that they tend to be much lower in iron than sodium bentonites, and therefore more suitable for white or light firing clay bodies.

The naming issue is kind of amusing.  Not sure where it's resolution gets us?

I would be more interested in knowing, when looking at the chemistry of a given bentonite, if a certain amount of sodium cations can make that bentonite swell even if there is actually more calcium cations as an overall %?  Put another way, how much sodium cations does it take to create a swelling bentonite, and does the presence of calcium cations interfere with this, and if so how much.  Have not found anything on this issue yet, but if I could, it would probably go a long way to offering a practical way to name bentonites...

Your observation that many calcium bentonites have lower iron than sodium bentonites is interesting.  If low iron ingredients was a priority in your clay body (as opposed to plasticity or something else, this could be a reason to just use the calcium bentonite outright, without trying to mess around and change it to something else.   Too much swelling/plasticity/etc would just get in the way of adding lots of it.   The small particle size of smectites in general is very attractive as a feature, as you throwing experience seems to suggest, and is a good reason on its own to be looking at these materials in my view.   

 

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On ‎4‎/‎02‎/‎2018 at 9:14 AM, Sequoia Pottery said:

Curt:  I went back and more carefully read the previous posts.  The idea of adding calcium bentonite to a clay body for "packing" purposes, to make for a better clay body, regardless of any improvement in "plasticity".  Let's try it!  The clay mine I mentioned near Death Valley also mines a mineral called "sepiolite"  it is a magnesium silicate related in some way to talc, and possibly asbestos.  I think.  I experimented with it also, and made a low-fire, cone 05 clay.  Extremely small particle size also.  it does not gell, and I could not get it to gell by any additions.  The cone 05 clay body threw amazingly well at about 30%, I have notes somewhere.  It shrank a lot, however, maybe about 17%?  I made one attempt at a glaze that fit it, soaked it in water, etc, it does not lose its ring, appears quite strong.  It is porous, but don't remember a number, but that could probably be manipulated.

So if that kind of addition seemed to work with sepiolite, why not calcium bentonite?  And there is a lot of calcium bentonite all around the world.  I'm going to try it.  Thank you.

This!

In foundries, the useful attribute of calcium bentonite was adhesion - making sand grains stick together for casting, etc..    Nothing to do with "plasticity" as we have traditionally understood it, probably quite the contrary.   Too much sticky plasticity just makes the material itself and anything you put it in to difficult to work with.  There is a giant hint here for us potters from industry I think, namely, if you have big grains of something refractory (eg, sand), you can get them to stick together in the shape you want when forming by using something sticky - but not TOO sticky - like calcium bentonite (or sepiolite, or.., or...).   I think there is direct application to clay bodies here, and the size aggregates we put in them.  Normally we would be thinking about ball clay for some kind of small particle, intermediate strength plasticizer, but maybe we should be looking at other alternatives.

This also casts light more generally on the mechanism of how I think smectites of all sorts can assist us once we stop thinking of them only as bulk plasticizers, and start seeing their wider mechanical advantage in a clay body. 

As for your experimental clay body, 17% shrinkage does not sound so bad, almost in the realm of "I can find a way to work with this."  I can think of some very expensive clay bodies that have fired shrinkage only just less than that...   As for porosity, yes that is just a chemistry/materials adjustment issue I think.  Probably have to add in some feldspar, etc.. Standard clay body chemistry stuff.   Or fire higher!

 

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1 hour ago, glazenerd said:

Curt:

i would have to agree wholeheartedly with your comment above. Yes, I did highly generalize the Ca/Na content: combined they make up a small % of the chemistry. Factually, all bentonite should be classified as magnesium: most are above 20%. After that, classified as swelling or non- swelling. In relation to clay chemistry: the alumina content would be deciding influence for me; although it would have to be non- swelling. The alumina content reflects plasticity; as the alumina content falls, the plasticity rises. I covered that relationship in the Cation Exchange article: CM 1-18. I would also agree any bentonite could be used as a plasticizer, but effectiveness waivers. One of these years I will finish the " plasticizer" table I have worked on for years. 

In regards to clay chemistry as a suspender: non-swelling should be the only choice. In the States, bentonite tends to be as one general product. Like clay, the cheaper the bentonite. Off topic, but it always makes me chuckle: the primary use of bentonite is drilling mud for oil wells.

side note: most bentonite as I recall run 0.25 microns and under. Been awhile since I have looked at that table section. Like most clay nerds, I have tried 6-8 different varieties. In testing, the relative differences in plasticity were minimal at best. As other posters have  attested: increasing % seems to be the only differing value. 

Yes, the magnesium can be a big component of smectites.    The desire to avoid having too much magnesium in my clay bodies has been a practical limitation on how much I have been adding so far.  In the saponite I am looking at this is definitely an issue.  

If there is some kind of general link between alumina and plasticity I probably need to see a lot more research to get any comfort with it, but that is another topic.  Regarding  bentonite and other smectites, what I have seen so far suggests that the mechanism of their plasticity relates mainly to swelling behaviour as the relevant attribute.  However, in this thread I am hoping we can avoid having plasticity dominate the discussion, as this has been (and still is) much discussed elsewhere.

I think smectites are generally much smaller than .25 microns when hydrated.  The studies I have seen tend to measure everything in angstroms, or possibly nanometers.  Their very small particle size is one of the things that makes them so unique as clay body constituents.

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First, on the general format of this "media", which I have never participated in before.  Is it more clear to "quote" and respond, or just let her rip?

Anyway.  The shrinkage.  Yes, 17% is manageable, but remember that is at cone 05!  In the meantime, I am trying to get larger (50-pound sacks) of sepiolite and bentonite from the mine in California, which has since been sold to a large multinational corporation. These people really do not want to deal with us.  I did order a 50-pound sack of "calcium" bentonite from "Millwhite Inc", in Texas.  Apparently, it's on its way.  I am going to do exactly what you suggest, add a lot of it, say 15% to 35% kaolinite, 30% silica and 20% feldspar and see what happens.

How to tell calcium bentonite from sodium bentonite.  If you look at the formula, the calcium bentonites will have more calcium and less sodium.  Often the calcium is just impurities of calcium carbonate, not tied up in the clay crystals.  I have never noticed any impurities of sodium, what could that be?  Calcite is abundant everywhere.  Maybe a rule of thumb is if it gells it's sodium bentonite and if it does not it is calcium bentonite.   That seems to be what we are interested in any way.  Maybe the conversation is really about gelling and not gelling?

Magnesium in some of these smectites (hectorite and sepiolite and attapulgite) could have a detrimental effect on HIGH fired clay bodies, but I don't think that would be a problem with low fire bodies.  "bentonite" by definition does not have magnesium, at least not in the clay crystals.  Speaking of attapulgite, I ran across a commercial additive called "acti-gel", which is apparently attapulgite, very similar to sepiolite, magnesium based.

I sense we three agree on one thing:  the small particle size of "smectites" deserve more investigation as to including in a clay body both for that property alone and for improving "plasticity".  Again, let's do it!  Apparently, we are not in agreement on that gelling thing.

And about "gelling".  A clay body is not kaolinite alone, it has the gigantic particles of silica and feldspar or powdered rock, which are generally not plastic at all.  Here's a test about improving or creating plasticity of those materials.  Take 500 grams of silica and add 100 grams of both a gelling smectite and a non-gelling smectite, and see which mix is more plastic.

Drilling mud in oil fields.  Yes, sodium bentonite's primary use is drilling wells.  There are many other well drilling chemicals that may be of use to us potters.  I live near Bakersfield, California, which is the oil hub of California.  A couple years ago I got a 50-pound sack of "poly-anionic cellulose", which works exactly like CMC, except better, at about 1/10th the price.  I would go back, except they will not allow me to haul anything away in my van, they will allow, they insist on a pickup truck only.  Fascist Company Rules.  So one of these days I'll borrow a pick up truck and drive to Bakersfield and try to figure out what they have.  They DO have a sodium bentonite with a chemical additive  that apparently makes it gell even more, I think with the term "methacrylide or methacrylamine" in it. Drilling mud construction is an art and science of manipulating the rheology of a well bore.  We are trying to do the same thing in a clay body, right?

 

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Tom:  I did see that assertion in Ceramic Science For the Potter.  I'm not buying it. :).  Also, he's talking about kaolinite, NOT a working clay body, which includes very non-plastic materials as well.  The proof is in making a side by side comparison with gelling and non-gelling bentonites both in pure clay and in an actual clay body.  I have done that, and gelling is better in my experience.  I DO think you could add far more calcium bentonite in a clay body than you could sodium bentonite, but I haven't tried that except for that one test with sepiolite (non selling magnesium smectite).

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Particle sizes in microns has been the pottery standard for decades. I switched to SSA awhile back.

references to  the small particle sizes of smecites. Let me give you a visual reference of specific surface area (SSA)

1 teaspoon of hectorite will cover 750 sq. meters, or 697 sq.ft. If laid end to end. ( end to end we call mesh)  0.25 micron bentonite would cover less than half of that. 

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On ‎8‎/‎02‎/‎2018 at 12:16 AM, Sequoia Pottery said:

First, on the general format of this "media", which I have never participated in before.  Is it more clear to "quote" and respond, or just let her rip?

 

Ray, 

There are no rules around this that I am aware of.  I think it depends on the situation and it is up to you. 

If it is obvious what we are talking about I would say no need.  However, that is not really the case here.  There are several things being talked about at once, so identifying the specific thing you are responding to would seem to make sense.  Just my take.

 

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On ‎8‎/‎02‎/‎2018 at 12:16 AM, Sequoia Pottery said:

am going to do exactly what you suggest, add a lot of it, say 15% to 35% kaolinite, 30% silica and 20% feldspar and see what happens.

Will be interested in your results.  I have started down this road, but haven't done enough yet to learn anything I am confident in reporting here.

 

On ‎8‎/‎02‎/‎2018 at 12:16 AM, Sequoia Pottery said:

Maybe a rule of thumb is if it gells it's sodium bentonite and if it does not it is calcium bentonite.   That seems to be what we are interested in any way.  Maybe the conversation is really about gelling and not gelling

I think this is an interesting approach.  However, it is pretty clear to me that there are degrees of gelling.  Or swelling.  Or both.  Or...?  If I go look at the rigorous definition of a gel, it seems clear that sometimes sodium bentonite in water behaves like a gel, and sometimes it is more like a liquid.  Really depends on the amount of water.  Same is true for the calcium bentonite (saponite) I am looking at at the moment.  The difference between the two is just a matter of degree.   Hmmm....

On ‎8‎/‎02‎/‎2018 at 12:16 AM, Sequoia Pottery said:

the small particle size of "smectites" deserve more investigation as to including in a clay body both for that property alone and for improving "plasticity"

Agreed.  The particle size aspect of all the smectites is of great interest.  Also provides a more productive path forward than the idea that there is just sodium bentonite vs everything else.

 

On ‎8‎/‎02‎/‎2018 at 12:16 AM, Sequoia Pottery said:

"poly-anionic cellulose", which works exactly like CMC, except better, at about 1/10th the price

Will see if I can get some of this locally. 

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I looked up my notes about using 20% (actually), sepiolite in a cone 05 clay body.  I  got 20 percent shrinkage after firing and had close to 0 absorption with 10% frit 3124 (boro/calcium/alkali.  About gelling, you said, " Same is true for the calcium bentonite (saponite) I am looking at at the moment.  "  I have a one pound sample of the following saponite, but it has
WAY more calcium than advertised, so I didn't really experiment with it very much.  All of these materials are of very small particle size.  Hey, please post what happens with your 15-35-30-20 experiment.  

TYPICAL CHEMICAL PROPERTIES %_
TYPICAL PHYSICAL PROPERTIES
PACKAGING
IMVITE 1016 is a gelling clay obtained from saponite clay, a magnesium bentonite.
1 (Fresh Water)
Yield, (bbls/ton) ............................................................. 95
Viscosity, Fann @ 6% solids 600 RPM, ......... 30 min. overnight
Plastic Viscosity, (cps) .................................................. 3-4
Yield Point, (lbs./100 ft) ............................................... 29
Water Loss, (cc) ........................................................... 19
For test procedure in API 13A and 13B..
Fann Viscometer dial reading at 600 RPM.
Silicon (SiO ) .................................................................. 44.6
Aluminum (Al O ) ............................................................ 7.8
Magnesium (MgO) .......................................................... 22.8
Iron (Fe O ) ..................................................................... 2.5
Calcium (CaO) ................................................................ 4.5
Potassium (K O) ............................................................. 1.3
Sodium (Na O) ............................................................... 2.5
L.O.I. (1000 C) ............................................................... 14.0
 

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On 2/7/2018 at 7:08 PM, glazenerd said:

Particle sizes in microns has been the pottery standard for decades. I switched to SSA awhile back.

references to  the small particle sizes of smecites. Let me give you a visual reference of specific surface area (SSA)

1 teaspoon of hectorite will cover 750 sq. meters, or 697 sq.ft. If laid end to end. ( end to end we call mesh)  0.25 micron bentonite would cover less than half of that. 

I've seen those kinds of figures with most  "smectites", and it's still hard to imagine.  You'd think those tiny particles would help fill in voids in a fired clay body.  About filling in voids, THIS is interesting,  https://www.sciencedirect.com/science/article/pii/S1877705813008060

 

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