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Posted 22 May 2013Thanks, everybody. You've all been helpful. It's sorta my "Duh!" moment because I should have figured this out a year ago.
Posted 22 May 2013what's your process for reclaiming clay? how long are you aging for?
when clay dries out, it loses pretty much all of the plasticity and has to start over once reconstituted - so if you're using reclaim that's been dried out and didn't have time to sit in a slop barrel/slake down for a decent amount of time to allow bacterial growth, this could be why. if you're making fresh clay from dry-bagged material, same thing, it needs to "age" and get funky from the bacteria that make it more plastic (due to acetic acid excrement); also there's the issue of the clay particulates not being fully saturated yet if using dry material, which adds to shortness since the particulates lose much of the meniscus of water surrounding them once they soak up this water when it equalizes -- usually mixing a wetter batch of clay will help this a tad.
as for plasticizers, you can add other things besides beer to make it more plastic (beer provide more bacteria/food source). simply adding more clay with organic content (like ball clays) can also help. industry typically uses bentonites/hectorites, VeeGum T, or cellulose/vegetable gums to help modify the body and be more plastic. immediate plasticizers to try are vinegars or epsom salts, both of which I believe change the chemistry making the particles negatively charged/more acidic, essentially flocculating the clay body.
Thanks, Perkolator, I know most of what you point out above so that's why it blows my mind that the pugmill seems to ruin my clay. In my first life as a potter I used a Walker that was as much or more a mixer than a pugmill and a large blue bird. I'd age trash cans of clay for 3 or 4 months and it was good. Now I use a Peter Pugger and I've got clay that has been in bags under a tarp for 11 months through a Georgia summer so it has a fine, thick coat of green slime over the outside but the clay is no more plastic than the day I pugged it.
Here's what I'm finally thinking: Any pot that I destroy while still wet, I just wedge up almost immediately and it is okay. what I pug is almost all pots that were completely dry and ready to bisque and I tossed when I realized they weren't good enough to fire, so my guess is that during the throwing, enough of the most plastic parts of the clay body were washed away. So, I'm thinking that I just need to replace those fine particles when I pug with, as you suggest above, ball clay and maybe a little bentonite? The reason I'm asking for advice is that I don't crank up the pugmill unless I'm going to pug at least 500 lbs and haven't tested my theory yet. What you say about vinegar and epsom salts is interesting. I use epsom salt in glazes but have never used it in a clay body. I may test that at some point but right now I'm more interested in just replacing what was washed out.
Ball clay is probably the best thing to add, right? Should I add a little bentonite? Any other fine particle clay? I have the same problem with porcelain. Will ball clay make porcelain less translucent?
Thanks in advance for suggestions from anyone.
I have only been using a pugmill for a few years but for what it's worth: I mix fresh clay out the box with trimmings, dry pots, and yes the dreaded splashpan mess, including the sloppy slip throwing water that accumulates in the bottom of the pan, I'll also throw in throwing water instead of fresh tap water. Usually about 1/2 scrap and 1/2 fresh clay. I was always under the impression that the throwing water or splashpan sludge contains the finer particles that aid in plasticity. I usually mix up the clay a day or two before I need it and it's good to throw.
If you need to add a plasticizer I would go with macaloid. 2% will plasticize a porcelain body containing no ball clay whatsoever so even 1/2 or 1/4 of that amount would probably suffice, might be a pain mixing it and getting the weights right though. Ball clay additions are going to mess up your non porous clay unless you then add more flux to it. Plus ball clay often contains lignites which also would be an issue with a white clay.
Thank for the info! BTW, who are you Masked-Person-From-The-Great-White-North-Who-Know-A-Lot?
Posted 22 May 2013Hi,
As everyone already knows I am very primative and still use a splash pan....WHATEVER! my eyes are too tired....
Anyway back on the topic. Firstly I don't pug my own clay but my neighbour pottery does. I know he pugs from reconstituted clay that has been totally dried out first, pulverized and then water added. We have had conversations about the fact that the water in this area it very very hard. I know he adds a floculant / epsom salt. How much ect not sure but can find out. I will say though I have used his clay and sometimes it is a bit short and sometimes not. I am guessing he isn't that accurate with the amounts.
This might be of some interest to you: http://pubs.usgs.gov...334g/report.pdf
I haven't read it myself as it has some pretty big words but was impressed by the number of pages.
Holy Crap, T! I'm not reading that. That looks like something John B would read. But thanks anyway.
Posted 22 May 2013My daughter has a pug and it eat clay all the time.. It's called pica, the uncontrollable urge to eat clay. It also processes that clay in my back yard every time she comes to visit. It's also short and not very plastic...
Oh. I'm sorry. You were talking about your pugmil....My mistake..:Psrc="http://ceramicartsdaily.org/community/public/style_emoticons/default/tongue.gif">
Jed, processing dug clay is one of the main reasons I bought a pugmill. I know you live near some neat park in Utah but I forget which one. What's the clay like there that your daughter digs?
Posted 22 May 2013I also use a splash pan which I made myself out of wood. I don't own a pug mill. I save all my throwing water and slip, with leather hard trimmings. I let this age in a 5 gallon bucket, then dry it out on a plaster bat.Could you be putting too much dry material through your pug?
Maybe its all that Lizella clay.[joking!].
TJR. add" creepy" smiley face here.
I use a lot of different clays, but probably the one I use the most is cone 6 B-Mix. I think that's the problem. My reclaimed clay has no clay from throwing water and slip that has been dried.
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