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How Much Difference Does A De-Airing Pug Mill Make?

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I'm thinking about upgrading my old bluebird  non de-airing  pug mill to de-airing. Since this may be a lot of work, I want to make sure that, in practical terms, it really makes a meaningful difference to have the de-airing feature.

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Idaho Potter

Idaho Potter

Learning all the time

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Posted Yesterday, 10:48 PM

The main difference, between de-airing or no, is not having to wedge the clay. You turn on the de-airing vaccum while still mixing the clay. Then, leaving the vacuum working, you switch from mixing (let the auger completely stop) to pugging. After you have emptied the pugmill, turn off both the vacuum and the pugger. For heaven's sake, remember to open the vacuum line and release the pressure. By the way, the vacuum pressure should be between 20 & 25 PSI before switching from mixing to pugging.

 

I use reclaimed clay for throwing, else why have a pugmill? Mark, I don't work in porcelain, but porcelain is why they finally came out with a stainless steel Peter Pugger--because it's not supposed to compromise the clay.

 

I've had my Peter Pugger for almost eleven years, and my back and wrists thank me. It may keep me playing in the mud into my nineties, which is better than hanging out at the senior center's bar.

 

Shirley

This may help.

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The other reason I think is that feeding bagged clay through pugger allows for the clay to re orientate from the 8x8 block down to a smaller workable pug. Clay in 25 lb bags start to setup some and you also need to change the spiral that the larger pug mill introduced.

Because some clays like Bmix or Loafer Glory can be quite firm, the pugger can change the clay to soft plastic throwable clay by going through the pugger, same as wedging does

Wyndham 

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John Baymore and others have convinced me that air pockets in ware do not cause ware to explode in the kiln firing.  What apparently matters for the exit of water and burn-out gases is the total clay thickness, minus the thickness of any void in the clay.

 

As a consequence someone has asked me why anyone bothers to de-airing clay?

 

I don't have an answer. 

 

Is it just a tradition to de-air clay or does it make the clay better in some way? 

 

It's seems like an aerated clay could be just as useful as an airless clay, although the cohesive plasticity would be lower.

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If you are getting airbubbles in the clay......... more arm (as in wedging more).  ;)   (.....more cowbell!.......)

 

Air bubbles in clay are not the explosion generators... but they are REALLY annoying when you are throwing on the wheel.  Also in a highly pyroplastic clay, a small airpocket in the body wall CAN tend to expand a tiny bit making a small "blister" on the surface.

 

best,

 

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

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I use drop wedging for the initial forming of slabs, while the potters rams horn wedge.  We all agree these actions temporarily make the clay less hard (penetration plasticity) and more cohesive (cohesive plasticity).

 

a.)  Big Ceramic store tech pages suggest wedging or pug milling mixes more dry areas of the pug with wetter areas;

b.)  according to the Alfred Particle Orientation Lecture, wedging mixes weak shear planes create by the manufacturers pug milling; 

c.)  my guess is it's more important that any type of wedging temporarily breaks up the static bonds between clay particles which have developed over time, allowing the clay particles to again easily slide past each other for a while. (An analogous situation is boiling water, which breaks the accumulated hydrogen-hydrogen bonds between each water molecule, permitting the boiling water to freeze into ice structure faster than room temperature water where the hydrogen-hydrogen bonds need to be first broken, giving off  heat, before they can freeze into an ice matrix.)

 

These processes all create greater cohesive plasticity, and greater softness (mechanical plasticity).  I suspect these changes are far important in imparting desirable clay properties than any particular particle orientation different types of wedging produce.  Given all this it seems like a clay mixer, as Neil mentions, should impart these same traits better than a pug mill as it doesn't impart the frictional clay shear problems pug mills can create.

 

http://www.bigceramicstore.com/info/ceramics/tips/tip75_pug_mills_clay_mixers.html

"It seems that only wheel throwers want clay that has been de-aired.  And many of the non de-airing pug mills on the market today mix the clay with very little air even without a vacuum.  Vacuums do tend to dry the clay out a little. And some potters don't like them because the vacuum is one more thing to break. But if you have a de-airing pug mill, the vacuum can be turned on and off as desired."

 

Creating slabs or sculpture, I slit any occasional air bubble I find to release and press them out.  It doesn't seem to be a common incidence.

 

We made a decision early on not to stop recycling clay primarily because our discounted price from nearby Laguna Clay provided savings of less than $1 per hour put into clay recycling as a large percentage of clay scraps or slop become slip - plus the fact that we typically stock 12 different clays, so the recycled clay had unknown COE and performed poorly both for throwing and sculpture.

 

Does my new understanding of wedging or mixing clay accurately reflect the benefits of why this is done before using clay?   Are there aspects I'm still missing or have wrongly understood?

 

If you are getting airbubbles in the clay......... more arm (as in wedging more).  ;)   (.....more cowbell!.......)

 

Air bubbles in clay are not the explosion generators... but they are REALLY annoying when you are throwing on the wheel.  Also in a highly pyroplastic clay, a small airpocket in the body wall CAN tend to expand a tiny bit making a small "blister" on the surface.

 

best,

 

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

 

John, isn't the biggest issue with air bubbles/ pockets in wares, that they are a structural weakness?

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John, isn't the biggest issue with air bubbles/ pockets in wares, that they are a structural weakness?

 

Yup, that too.  But usually there are only one or two... so not a HUGE issue. But it COULD be.

 

best,

\

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

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Mixers mix on a large scale, getting dry areas and wet areas combined into a consistent mix, but full of air, too. But for clay particles to bond well, they cannot have tiny air pockets between them. Each particle must be throughly wetted, with just a thin layer of water between each particle, as we discussed in our recent plasticity discussion. This is why non de-aired clay is often referred to as being 'short'. The clay particles don't bond as well, and the clay tears easier and doesn't hold form as well during the throwing process.

Norm Stuart likes this

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The other reason I think is that feeding bagged clay through pugger allows for the clay to re orientate from the 8x8 block down to a smaller workable pug. Clay in 25 lb bags start to setup some and you also need to change the spiral that the larger pug mill introduced.

Because some clays like Bmix or Loafer Glory can be quite firm, the pugger can change the clay to soft plastic throwable clay by going through the pugger, same as wedging does

Wyndham 

 

I often hear people talk about the spiral of the pugger, and have never found it to be an issue. By the time you cut up your clay and make it into balls, you're not dealing with a total spiral, but a small section of one. And if you wedge, you're creating a new spiral. And if you cone the clay during the centering process, any spiral that existed is gone, and replaced by a new spiral from the wheel.

WillowTreePottery likes this

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Now that makes sense.  An industrial scale mixer essentially demands a de-airing pugmill -- or the invention of one if they didn't already exist.

 

Mixers mix on a large scale, getting dry areas and wet areas combined into a consistent mix, but full of air, too. But for clay particles to bond well, they cannot have tiny air pockets between them. Each particle must be throughly wetted, with just a thin layer of water between each particle, as we discussed in our recent plasticity discussion. This is why non de-aired clay is often referred to as being 'short'. The clay particles don't bond as well, and the clay tears easier and doesn't hold form as well during the throwing process.

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Last year I began to have some pretty severe arthritic problems in my hands an wrists after 30 yrs of making pottery,  I had only used an old relic of a peter Pugger  borrowed from a school. I have upgraded to the new Shimpo mixer/pugmill

 http://www.tuckerspottery.com/tkps/index.php?page=shop.product_details&flypage=flypage.tpl&product_id=1859&category_id=163&option=com_virtuemart&Itemid=1

 

I am a walking ad for this machine.  I can mix and pug out about 100 pounds a couple of times a day and it is always the perfect consistency.  Easy to use, reconstitutes dry scrap in no time at all and it means far less waste in my studio.    Best money I have ever spent,   It deairs clay perfectly and if I want a bit more aeration or plasiticity i just don't run the vacuum as long or add some vinegar to the mixer.

 

Kathy

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That's one expensive machine. You must do a huge amount of pottery to justify it. I think you have convinced me to upgrade my little hundred dollar pug mill to de-airing.

 

thanks for the perspective

If you were closer, I'd offer your money back on your current mill.  Every time my students have to take time out of the project schedule to reclaim clay by hand/ forearm/ elbow, it pushes me one step closer, to buying a pug mill.

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I got mine on craigslist. They wanted $700 for it.  I offered to them $100. Since I was only one that had shown up with hundred dollar bills, they took it gladly.

 

They show up from time to time on craigslist. Just be diligent and you'll come up with one cheap.

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I got mine on craigslist. They wanted $700 for it.  I offered to them $100. Since I was only one that had shown up with hundred dollar bills, they took it gladly.

 

They show up from time to time on craigslist. Just be diligent and you'll come up with one cheap.

I keep looking.  Sadly, if any come up, they tend to be on the coasts.  I don't want one bad enough to drive that far.

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That's one expensive machine. You must do a huge amount of pottery to justify it. I think you have convinced me to upgrade my little hundred dollar pug mill to de-airing.

 

thanks for the perspective

I do a lot of wholesale and my hands were so bad I needed to do something to take the pressure off them. That was my primary goal and it's been great that way.  Clay comes out of the pug and I just wirecut into the size of piece needed.  My production has increased a lot and an added benefit is that I do not have any big garbage pails sitting around the studio waiting for me to reclaim them.Scraps and rejects go right back into the machine for the next batch.

I was also wasting a lot of clay simply because I hated to take the time to reclaim it .  By my calculation I have already saved myself about $500-600 worth of clay since I got it last June.  Also the time factor, I think I will have paid myself back in clay and time saved in the reclaim process and wedging by next fall.

I don't do much dry mixing in the winter because it's an indoor set up; but come spring, when the polar vortex abates here I will also save $ by being able to use dry bagged clay and not have to pay to have "water" shipped to me.  That will also represent a savings of about .07 cents/pound on clay.

 

Now to the point of the original question," is the clay better when pugged in this new machine than the stuff from the old Peter Pugger I used to use a couple of times a year,?' 

 

Unequivocally YES!  The dry mix and reclaim are a bit short sometimes but some vinegar and new clay easily compensate,  I also add some other plasticizers if needed but that's a different discussion.

 

I am a one person operation and that pricey little gadget is the equivalent to hiring someone two days a week to do the jobs it does.  I guess that is how I justify it.\

 

Kathy

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Agree with Kathy 100%.  Like having a studio helper with out attitude or opinions!  Don't know about non de airing myself, but students at a near by school use a non DA and hate the whole process.    The only thing the PP does not do really well is a combined wet -bone dry in chunks mix.  That I set up, add water to and mix a bit, leave over night, mix a bit, leave till after lunch, mix a bit, then pug.  On rare ocations, I need to run the pugs back through again, easy and quick.  Even at that, major hand saver.

No mater what the cost, it's cheaper that surgery or stopping throwing at this point.

I think people that don't have one, don't realize all the ways it can change your studio processes for the better.

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