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preeta

The Act of Pugging

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We have a non vaccum Peter Pugger at School.  i've just become involved with pugging clay.

But first pugging is another word for mixing clay right? So even though this is a Peter Pugger all it really does is mix the clay right?  so really this is just a mixer without wedging?

To recycle we put in wet clay and pieces of dry clay. and then turn the machine on. the longer you pug the fluffier the clay gets. then the clay is put in bags and aged - at least a month.

so here are my questions. first just to experiment i took some of the freshly pugged clay and threw a tall vase and a platter.  As i shaping the moon jar shape, cracks developed and the jar collapsed.  

the platter did fine till it came out of the bisque kiln with big right across crack that went right through.  mind you i had compressed and wedged the clay well.  the pugged clay was so full of air that you had to. i wedged well on the table as well as the wheel and also compressed the bottom well too. 

i also made mugs with the same freshly pugged clay  and really compressed both walls and bottom.  no problem. 

so my questions are:

why is the clay so short? about  60%  of recycled clay is from  handbuilding so straight from the bag  (mostly and  some recycled clay) and 40% wheel.  should we be putting some additives in the pug mill to make up the small particles lost at the wheel? 

should we keep the clay overnight in the pugmill and again mix it in the next few days if not the very next day? is there something called too much pugging (without a vaccum de-airer)

why do we age clay? what happens with aging.  is it just about mixing so that there are no drier/harder clumps? to even out the wetness of the clay? 

 

 

 

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The clay is short because pugging isn’t really the best way to mix clay.  Pugging is more like large scale wedging.  The dry clay isn’t fully wet, so the clay particles aren’t fully lubricated, and so the clay is short.

The practice I’ve seen is to get the clay wet enough that it’s a slip, then pour this out on a plaster slab (or into canvas bags, if you’re like me) where it’s allowed to dry to roughly the consistency you want.  Then you pug.  

The ideal is always that you want the clay to be way too wet and bring it back.  That way all your clay particles are nicely lubricated.

Aging does help improve plasticity.  If I’m honest, I’m not 100% on why, but the best answers I’ve heard are that the moisture does even out a bit and that the organic particulate matter rots out a bit.  Moldy clay throws nicely.

 

Edited by Tyler Miller

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If any of the clay is dry that you pugged it will take some time to get it wet as Tyler said above. The best practice is also put some clay goo (the stuff that collects in your splash pan in the mixer with every batch. This has the good stuff in it and will help every batch.If your ingredients are dry at all add a small amount of vinegar as well.Let that dry clay age some if it had dry stuff in the mix.I'm assuming you are mixing stoneware clay?

I use my de airing Potter pugged only with wet materials (porcelain which does not rehydrate well)as I do not have room or time to age it. 

If you think about pugging it really rips clay apart then compresses it out the barrel.The Petter Pugged you are using is the old style-which is great mixer and does the pugging only it does not remove the air. The newer machines remove all air which is huge.

Try the adding splash pan clay and vinegar to the clay and let it sit some weeks.Foe small pots this Amy not matter as you found out.

The clay will not have legs until its ages some (legs are what makes it throw large) and well.

Edited by Mark C.

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Unfortunately we don’t have space for preparing clay the proper way.  Not for the matter the man power.  But Tyler the wet clay is a mix of clumps and slip in the buckets they sit in. We have vertical space, not horizontal. 

Mark I keep saying one should put the bottom of the water bucket and the splash pan in the recycle bucket to replace what is lost.  Instead I just see it trapped in the clay trap which we run from since it smells so when the trap is emptied. 

Mark the school bought the non vacuum pugger which was available when they bought it 16 or 17  years ago. I think the biggest vacuum puffer is smaller than the deaired one and therefore the school insisted on the deaired one. Just like they insisted on a downdraft gas kiln Because of fuel efficiency issue. Some years ago they also changed from ^10 to ^6.

I guess we should pug/mix more often and then let it age. Usually the clay sits waiting for pugging mostly due to manpower issue.  

Since lubrication  is key then too much pugging should not matter.  At least it is mixing well.  

You have given me ideas I need to test to see if they work.  

The aim is lubricate.  And collect the splash pan residue.  

Edited by preeta

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On 6/30/2018 at 6:40 PM, preeta said:

Unfortunately we don’t have space for preparing clay the proper way.  Not for the matter the man power.  But Tyler the wet clay is a mix of clumps and slip in the buckets they sit in. We have vertical space, not horizontal. 

Mark I keep saying one should put the bottom of the water bucket and the splash pan in the recycle bucket to replace what is lost.  Instead I just see it trapped in the clay trap which we run from since it smells so when the trap is emptied. 

Mark the school bought the non vacuum pugger which was available when they bought it 16 or 17  years ago. I think the biggest vacuum puffer is smaller than the deaired one and therefore the school insisted on the deaired one. Just like they insisted on a downdraft gas kiln Because of fuel efficiency issue. Some years ago they also changed from ^10 to ^6.

I guess we should pug/mix more often and then let it age. Usually the clay sits waiting for pugging mostly due to manpower issue.  

Since lubrication  is key then too much pugging should not matter.  At least it is mixing well.  

You have given me ideas I need to test to see if they work.  

The aim is lubricate.  And collect the splash pan residue.  

Kudos to you for helping out your clay class, it's not a job I'd want. 

This is funny because at the first college clay classes I took they had everyone use clay out of the pugger also, joking about how it had student hair and fingernails still in it from 1975, not to mention sawdust, insects, gravel, the occasional cigarette butt, and such. They weren't kidding. It was extremely short also, which made student's first efforts much more difficult. A simple explanation of why it sucked and that it needed aging/wetting would have made a big difference but I assume they pushed everyone to use it raw because it was more labor and time to fix it properly and the college wouldn't pay an aide to do the work. Being extremely broke at the time like most of the kiddies "free" clay seemed like a good deal compared to shelling out for a $15 bag. Considering how many projects from that class I attempted that cracked or otherwise failed in the kiln clearly that was a bad call. When I got my first bag of commercial clay I was astonished how easy it was to make things. 

Edited by yappystudent

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Repugging it is fine.

I get dogears to start with often as clay has stood in pugmill a length of time.

I use cloggy clay of  different moisture and add stuff from my wheels slop bucket. Folk also add bentonite.

There are threads here discussing the probs of reclaimed clay and  plasticity.

Not too many folk have time or space to completely slurry, sieve and dry out all clay so what you're doing is fine with Marx's suggestions and pos. Addition of a plasticiser.

I use straight from mill for smalls, just measuring off a known length for items, and wedge for bigger stuff 

Search the forums for reclaiming. Workability and plasticity

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Preeta, maybe you could recruit a few classmates who are also having trouble to experiment by ageing smaller amounts and sharing their opinions. Understanding results while getting a bit of science as a cooperative experience could help them create sensible and useful recycling rules for all.

(and less smelliness to clean from the sump)

Edited by Rae Reich

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Some pundits point out that wet clay bits thrown in water don't turn to mush very fast, whilst dried bits do, hence advice - allow bits, scraps, chunks, and baddies (bad pot!) to thoroughly dry before slaking, which I'm doing now. All the slop goes in there as well, including what's at the bottom of the bucket after standing for a while (doesn't take long for all the particles to settle, leaving clear water on top), can't see putting clay down the drain generally, nor particularly, as we're on septic. When the bucket's full, the big drill with mortar mix attachment gets it homogeneous quickly enough, then it's wait until dry enough to work with again.

I'm no expert though - will get back after some years! ...curious about the aging idea, my scraps were soaking several weeks before being mixed and then it took a few weeks to dry them out as well. I get less plastic as time goes by, hmmm, maybe spend more time in the pool?

Now I've an idea how much doesn't end up in finished pieces, I'll be taking home my scraps from next semester's Wheel II class...

Edited by Hulk
redunant redunant word word removed removed

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I don’t believe in putting dry pieces of clay in a pugmill or mixer, if that means the ratio of dry clay to liquid is unknown. When pugged clay is too short, the simplest answer is that it is missing moisture. If the liquid ratio is wrong to begin with, aging the clay can only do so much to improve it. 

I am a “slake everything” person too. Dry out the sludge to the consistency you want, then use the pugmill to homogenize. Drying out sludge on plaster doesn’t need to be a horizontal operation. It can be done vertically too. I made these plaster batts in 9x12 foil cake pans:

8EFBCBC9-7535-4006-BB33-A4CDF5555824.jpeg.7949be32e679bc88e4591c9b122e029c.jpeg

My studio consumes about 3000 lbs of clay per year. Compare that to your studio’s consumption to decide if this operation can be scaled to your studio. I make these clay/plaster towers every two weeks or so. Also, although damp plaster will hold the clay in a ready state for maybe 8 hours, the clay needs to be removed sometime in that window. So ask yourself if the timing and oversight requirements will work in your studio too.

If you cannot make the “slake everything” approach work, I would make the effort to figure out, through trial and error, a “formula” for the ratio of clay types that go into every mixer batch. i.e. For every pound of dry clay, add x.x. cups of wet clay (clumps and slip) and x.x cups of liquid. The fresh clay scraps generated by handbuilders can be added with no additional liquid. I would post this formula on the wall next to the pugmill.

That’s how I would do it, but I am a stickler for measuring, and believe in doing things consistently as much as possible. 

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This problem is being dissected from the final result. How about we start from the beginning:

1. Was the original clay blend from a recipe, or commercial mix? Do you have any info on its origins?

2. How many times has it been reclaimed? Does all the reclaim come from the same original source, or does the shop blend various clay blends?

adding more water is pseudo- plasticity: not plasticity. When you threw it on the wheel and it collapsed has already told you: no moe water please- you have moved from plastic limits ( firm clay ) to liquid limits ( exceeded maximum water absorption.) "plasticity" is one of those clay definitions that has moved from its original science term to pottery lore. Once you move past the (WOPL) water of plasticity of a given clay blend by adding more water: the water is merely a lubricant that creates a pseudo plasticky. Plasticity is created by negative ionic exchange... Blah blah blah...

nerd

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22 minutes ago, glazenerd said:

This problem is being dissected from the final result. How about we start from the beginning:

1. Was the original clay blend from a recipe, or commercial mix? Do you have any info on its origins?

2. How many times has it been reclaimed? Does all the reclaim come from the same original source, or does the shop blend various clay blends?

adding more water is pseudo- plasticity: not plasticity. When you threw it on the wheel and it collapsed has already told you: no moe water please- you have moved from plastic limits ( firm clay ) to liquid limits ( exceeded maximum water absorption.) "plasticity" is one of those clay definitions that has moved from its original science term to pottery lore. Once you move past the (WOPL) water of plasticity of a given clay blend by adding more water: the water is merely a lubricant that creates a pseudo plasticky. Plasticity is created by negative ionic exchange... Blah blah blah...

nerd

Most collage reclaim is really a mixed bag of all unknown stuff-mostly commercial blends. They may even blend white with brown clays-I have seen it all.

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@glazenerd “short” clay and “non-plastic” clay are not always the same thing. 

If the clay is a nicely plastic commercial claybody before being recycled, it won’t turn into “non-plastic” clay in the normal recycling iterations that pottery studios do. Especially not in the way @preeta described, which is that 60% of the recycled clay is fresh clay trimmings from handbuilding. It is not being processed enough times to change its composition noticibly. But it can become “short” from a lack of moisture. 

Edited by GEP

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Mark:

correct, why I am trying to figure out the source materials. Being short May not be as simple as assumed, but then again...

 

Mea:

also correct, with some notations. WOPL(water of plasticity) is the exact measurement of plasticity variables. 30 or above is considered plastic: 30 being the least and 38 being the most for typical ball clay. Kaolin runs 24-26, EPK is 26 and called plastic. ( coughs). When blended in a recipe: WOPL runs 18-24 typical pending recipe, plasticizers, and other plastic clays. Silica, feldspar, and grogs are non-plastic materials because they have no ability to hold or absorb water. Most blended bodies can lose up to 20% of their moisture content before the water film becomes depleted to the point of mechanical failure. Short is defined as a lack of plasticity due to inadequate cation exchange. Although in the last two decades, most of the clay chemistry science has been lost.

kudos to your clever way of maximizing studio space for reclamation. Functional indeed.

 

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so mea, you slake first? you get all your clay bone dry and then  add water to it? and take the slaked clay and put it on the plaster?

Tom

1. Leftovers of ^10  commercial clay. mainly one clay body (low iron content) but there is a bunch of other clays - black, brown, white, porcelain, with grog, without grog. Yup just as Mark said. 

2. The first month and last month - the type of clay in the recycle bucket mostly recycled clay from recycled clay blend. about  a month into classes the good stuff  starts landing into the recycle bucket.  5 months of classes. here's the thing about wheel throwers. the philosophy of the studio is reuse the ball of clay as many times as you can. you wont see kids sitting with 10 balls of clay. you will see them sitting with 3 balls of clay, then rewedge the clay and throw again and again and again  till they have used it all up in one sitting (this is not a wheel throwing  focused curriculum. there are no wheel throwing classes. its just kids who want to throw on the wheel out of personal interest who do. all 10 wheels are used at every class apart from the first month of class. )

 i have thrown with some of the clay balls the kids thrown. hardly any fine clay left. tear my hands - rough surface while throwing and trimming. so much grog.  but they use the same clay for handbuilding and wheel throwing. 

But Mea here is the key. they mix the bone dry clay in the wet and pug. let it sit for a day or two and then pug again. then they wedge. i have helped with the wedging and usually the clay is very wet. just at the edge of being too wet. its wedged a lot to take the moisture out. so would it be a question of wetness? 

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3 hours ago, glazenerd said:

Although in the last two decades, most of the clay chemistry science has been lost.

Wait what?! Lost?! What do you mean?

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Maybe means words which hold meaning at one point are used or abused so many think they mean something else. 

Plasticity and workability....different tests...clays can be quite "plastic" with some uses of the word but not workable.

Hamer and Hamer discusses this in layman terms.

All this stuff we didn't think we neededto understand as Art students...arggghhh

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Preeta:

given the information supplied: the 60% of wheel scraps could have been thrown multiple times, and or reclaimed multiple times before that 60% went into the pugger? Obviously the grog content is high by your description of rough on the hands. So the clay has gone from cation exchange ( CEC) to anion exchange (AEC). Negative electrolytic charges produce deflocculation ( repulsion of adjoining particles- plasticity), to a neutral or positive charge ( AEC) resulting in flocculation.( attraction of adjoining particles.) What potters call short, is actually a form of flocculation resulting in agglomeration of colloids. ( enough science yet?)

Plasticity is the result of negative ionic charges in the water film. The amount of water required to form a pliable ball is called WOPL ( water of plasticity)  in application; the amount of water required to transfer electrolytic charges between clay particles. Water is not used to produce plasticity, it is used as a medium to transfer electrolytic charges between particles. Exceed the required amount: then you have gone from plastic limits (PL) to liquid limits (LL).  Once you cross into the liquid limits: potters call that " fat." 

Particle distribution, CEC, and PH all play a role in determining plasticity.  The focus of potters is particle size distribution: the finer the particle, the more plastic the material. There is some truth to that, but not entirely. As a clay particle gets smaller ( sub- micron), the amount of alumina decreases. The higher the alumina content; the lower the cation exchange. The lower the alumina, the higher the cation exchange: which equals plasticity. That said: your reclaimed clay has reached the point where it is no longer able to transfer cations: adding more water will do absolutely nothing besides weaken its mechanical structure. iE: add 2 quarts of OM4 to your slop bucket fines, let it sit over night: then add to the pugger and mix. Test, add 2 more quarts if it is still " short" when you do the next reclaim.

i will leave off the discussion of 2:1 and 1:1 clay particles, and how they absorb water, exchange cations: and their effects on plasticity and green strength. Nor will discussing the difference between flocculation, agglomeration, and coagulation help you much. It would help if potters stopped calling anything finer than 0.30 microns bentonite: not true either. However: in the daily life of a potter the science does not matter; the science only matters if you are writing a book on clay formulation with specific limits. So disregard my babbling, get some OM4 and fix your short clay problem. 

By the way: aged clay hits a point of equilibrium: which means cation exchange, molecular water absorption, and PH hits the point where no further reactions take place. While there is much discussion about the effects of organics on aged clay: organics have high cation exchange. The most plastic of all clay is humus (300 CEC) as compared to typical ball call (7.5 CEC). However it is never used in clay because of its high organic content. The clay would smell like a sewer pipe in a week.

t

 

 

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9 hours ago, preeta said:

so mea, you slake first? you get all your clay bone dry and then  add water to it?

My studio also generates a lot of fresh clay scraps from handbuilding. Just like you, those scraps go in a plastic bag, then straight into the pugmill again without slaking. If for some reason they were allowed to become leatherhard or drier, I would slake them. All of my wheel trimmings are slaked, spread out on plaster, then pugged. When I pug, it is usually a mix of slaked clay, handbuilding scraps, and new clay from the bag.

Thank you for providing more info about the way clay is used in your studio, and that you have experienced yourself how clay can be rendered overly groggy. I would suggest the recycling process that was used in the center where I used to teach. We had a few large plastic trash cans where students put their clay trimmings, plus empty their throwing water bucket into, and all the splashpan juice. Splashpans and buckets were washed out in these trash cans until they were almost clean, then finished off in the sink. Same with tools and hands. Students would get their throwing water by dipping a bucket into these trash cans. Only when the water was too thick for throwing were they allowed to get fresh water from the sink. With this method, very little clay goes down the sink, and the clay composition stays complete. You alluded earlier that splashpan juice was not being reclaimed. It’s not hard to capture all of those goodies. Instituing behavioral change among a group of people might be hard, but it’s not impossible.

I use a similar approach on a smaller scale at home. My throwing water comes from the sink, then used for days until it is too thick, then this water is used to slake the trimmings. I wash tools and hands in my thowing water bucket before finishing in the sink. I throw with little water so my splashpan does not accumulate liquid. 

Edited by GEP

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3 hours ago, glazenerd said:

<snip> However: in the daily life of a potter the science does not matter; the science only matters if you are writing a book on clay formulation with specific limits. So disregard my babbling, <snip>

 

As a student I get two responses from my teachers and fellow students.  Either strong dislike very openly or really like.  Because I need to know the why - the science,  the fundamentals.  So I ask “too many questions”. So your explanations matter to me as It gives me a starting point to experiment. I live to experiment! In life I need to understand the fundamentals - which got me into a lot of trouble esp. in my teens because I questioned everyone and everything.

i really want to understand the process of pugging not just how to pug well. So this thread is really helpful...

Mea that’s why initially I am a measurer too - to understand. 

Mea aaaaaargh. Water. Soooooo frustrating for me.... sooo frustrating. I have visited many campuses and clay studios here in Sacto and no one - NONE - of the places practise your studios method of collecting water and reusing it. That is what I’d like to see, to me that makes perfect sense... but unfortunately this idea of Uber cleanliness persists. Even during the drought when the teachers tried to restrict the amount of water used.

i have more questions but I gotta go now and will be back later.

 

 

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The basic issue is dry clay needs TIME to absorb water-this happens on a very small micro scale. So adding dry clay to wet clay and pugging it and letting it sit a few days then re-pugging it does not give it time to really absorb the water on that micro scale.

Better to slake it and then pug it. Or let it sit longer between pugging-either way clay takes time to get wet on this micro level.

Thats just the way it issue that clay will always be short the way its being treated now.

I have spent some time volunteering at an art center in the pacific-they use the same water bucket system as Mea discribe's above with one exception a white clay bucket and a brown clay bucket. The more throwing slop from the splash pans the better the clay is in the end.They also have two buckets for just plain wet clay a white one and a brown one.

As a production potter myself if my clay gets dry such as trimmings I toss it.I only pug my wet scraps.(this is all with Porcelain ) Clay is cheap enough for me as my time has more value. When I was young I spent lots of time messing with clay recycling and struggled with short clay. That was before great vacuum mixers. Also porcelains are much harder to bring around that stonewares in the reclaim world .

Edited by Mark C.

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Yeh Bernard Leach writes of this Japanese method of stacking  ofplaster bats clay sandwiches as used by GEP  and the reusing of water as it assists the colloidal formations in the clay, more plasticity forms. A case of water being not just water:-)). So this knowledge is not being passed on to many these days.

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Think reading for selves the chapters relevant in ceramicscience for the potter  WG  Lawrence will allow one to see the importance of charge in the clay world.

Who would have thought the making of mud pies would lead to this.

Wedging is meant to be better than pugging. Throw out the pugmill and start charging for the new workout classes with organic clay, can be grogged for exfoliating experience. Foot wedging sessions. No more heelcrackin' .  do it in the wine industry so clay people Let's go!

Edited by Babs
errors

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Preeta try to source the above book and Bernard Leach's A Potter's Book will answer lots of your questions.

The knowledge passed on by such giants has been lost to a generation of Potters .

Other knowledge  has possibly filled a space but when problems arise, this fundamental knowledge is the why practices are followed and with it it is just not the blind leading the blind.

A few folk here are down certain rabbitholes so when ferreted out by certain questions lend them an ear..then get to another source or3 , not wikip.PLEASE.... and form your own opinion

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Babs:

and hear I thought I was the only one who read W.G. Lawrence work on ionic charges. West, Lawrence, Grim, Olphant, and several Brit . Phd's have studied and written about cation exchange. Atterberg  developed his plastic, liquid, and shrinkage limits using the cation exchange properties of plastic clays. In Europe, it is common practice among clay makers to show plasticity levels of their products by a numerical Atterberg value. Cation exchange has been known in Ceramic Sciences and Engineering since the early 1900's. So when I told Preeta the science has been lost in the pottery world: this is just one example.

Preeta:

the most simple premise I can teach you about plastic materials is: watch the alumina content. When looking at the chemical analysis of any clay variety: kaolin, ball, bentonite, hectorite, or fhlorites: note the % of alumina. Once the alumina crosses over 28%, the plasticity levels drop dramatically. The most plastic ball clays have 24% and the least plastic have 28%. Bentonites have around 20%. Hectorites can have as little as 5%. Particle size decreases as alumina levels decrease: so it will save you much time trying to figure out what is more plastic. 

When you get to the point of wanting exact  details : then you can read studies like this one:

https://scholarsmine.mst.edu/cgi/viewcontent.cgi?article=6720&amp;context=masters_theses

given your current problem: you will find page 2 of the introduction (2, and 3 paragraphs) most applicable. iE: when clay has been wetted and dried multiple times, it can lose up to 30% of its plasticity.) 

tom

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