Pugging Porcelain- achieving a decent reclaim clay with pugmill

[Megga]

I have an old Venco de-airing pugmill, with an aluminum barrel. I'm starting fresh once again with an empty, cleaned out barrel. My intention is to pug my huge pile of porcelain reclaim clay all at once (over a few days, perhaps). Then I should just clean it out, because when leaving clay in it, I've repeatedly failed to get back to it in time.

 

I use ^6 porcelain PSH 910. Over many years I have never yielded reclaim clay that was a pleasure to use. I've always restricted it's use to a few items where the imperfections aren't as big an issue. But I feel like I should be able to do better, deairing pugmill and all.

Some of the challenges:

-When throwing, materials settle in the throwing water and form a hard lump in the bottom. (Primarily talc?) I've tried both adding this to the reclaim bucket (get dried gobs of material- but I could possibly deal with this more effectively in the future) and leaving it out has been my latest strategy. 

-As seems to be more common knowledge now, the aluminum barrel and porcelain clay react over time and form clumps of salts (?) that make hard horrible bits in your clay. A large part of my reason to try doing a big batch at once then clean it out.

-Getting the PSI high enough to de-air the porcelain is difficult

-The clay comes out short. 

 

The bags of clay have been sitting around for a long time. Any additives that I try now to improve the plasticity would be added as I pug. Ideas I'm considering:

-Adding some vinegar, because it would swing the alkalinity to slightly acidic, which would draw the particles closer together and possibly improve the plasticity.  

-I could mix some bentonite and water, and roll the clay in a bit of that "snot" before pugging?

-Epsom salts in the clay (straight from PSH) have not had good results for me. 

-A potter I worked for years ago used to mix her boxed clay 1:1 with the reclaim. But I'm nervous that the result would lower the quality of the boxed clay, more than improve the reclaim? 

 

Any brilliant thoughts and suggestions are appreciated. 

Edited June 16, 2022 by happy_pots

[Callie Beller Diesel]

Hi @happy_pots! 

I know you cross posted this question in a few other areas in the forum, but we find you get fewer duplicate answers, more engagement and a more concise conversation if it’s just in one spot. I have deleted one in a low traffic area of the forum, and I suggest that we keep the clay chemistry stuff on this part of the thread, and if anyone wants to offer advice relating to the pug mill itself can go Over here to the Equipment part of the forum. 

In regards to your question: The biggest thing that will make reclaim short is if you’re not thoroughly re-incorporating the fine particles from your throwing slop/cleanup bucket back into the mix. The fine slip from your bucket is a big part of what makes your clay plastic in the first place. In lots of cases it’s the ball clays, but can also include bentonites that are commonly used as plasticizers in cone 6 porcelains like PSH 910. I’d venture it’s bentonite at the bottom of your bucket, not talc. But even if it was talc, leaving it out of your clay’s composition could also affect its firing range, and the porosity of the finished ware, and would still be a Bad Plan. 

Mixing your reclaim in with fresh boxed clay can be a way of combatting the loss of plasticity, and would only really affect the “fresh” clay if the reclaim percentage was too high. I had mentors that would mix their reclaim into their fresh clay in the pug mill, and as long as it was kept at a minimum, there was no noticeable difference.

Another way of returning plasticity to your reclaim is to take a mix of 80% ball clay, 10% silica and 10% feldspar, and add about a cup of that to each gallon of reclaim slurry. No, it isn’t exact, and yes, it may alter the colour of your porcelain somewhat if you’re not using the same ingredients that the manufacturer did. If a slight change in warmth is acceptable to you, this is a good way to rescue the stuff you already have. 

Adding vinegar or Epsom salts may assist, but if those fine particles aren’t in the mix for the vinegar to act on, there’s only so much it can do.

I think trying to add bentonite via the method you suggest may not incorporate it thoroughly enough, but if you wanted to make an experiment, it would confirm or deny this suspicion.

Going forward with your new reclaim, you’re going to want to dump your throwing slop and anything from your splash pan\ into your reclaim bucket with some dry/botched pieces and your trimmings before it has a chance to settle out, and siphon off the water the next day. 

 

[Mark C.]

I reclaim a lot of cone 10 porcelain in an aluminum barrel Petter Pugger which has vacuum unit on it

Its always shorter than say new clay but the tricks are use planty of throwing slop from yiour bucket

I also never use dry clay in it as that really makes it short. Only wet scraps.

You can add vinegar aas well and let it sit after bagging it for a few weeks. I tend to use it for small stuff and right from the machine 

I never clean out the machine but it keeps wet as it sealed well with orings

I would not use those additives myself  (bentonite )

and yes adding new clay will help -but as you said it will lower the new clay a bit-I suggest you try the 50/50 mix new to old and see how that works for you.

cone  porcelain is such a different animal than cone 10 porcelain

Edited June 16, 2022 by Mark C.

[Piedmont Pottery]

Hydrated Veegum T added to the clay when mixing/pugging can do wonders for helping short batches of clay.  I've used it with stoneware and porcelain bodies with good success.  Being careful not to lose any of the fine particles when reclaiming is important, but easier said than done.  Veegum T can make up for some of the loss of fines.

[Mark C.]

I have some gum so next time I may stick in my shop blender to Hydrate the snot out of it then add a pinch

[Min]

2 hours ago, Piedmont Pottery said:

Hydrated Veegum T added to the clay when mixing/pugging can do wonders for helping short batches of clay.  I've used it with stoneware and porcelain bodies with good success.  Being careful not to lose any of the fine particles when reclaiming is important, but easier said than done.  Veegum T can make up for some of the loss of fines.

I like doing this with bentone ma (aka macaloid). For porcelain it saves the clay from getting specks from bentonite or loosing some whiteness with that and/or ball clay. But then again if it has ball clay is it really a porcelain? Opinions differ on this for sure. With whatever plasticizers are added I'ld use as little as possible to get the clay back to a suitable plasticity and I'ld check the absorption on reclaim before making a lot of pots with it if low absorption is necessary. Might need a bit of spar if it's too high.

Edited June 16, 2022 by Min

[Megga]

Thank you @Callie Beller Diesel. I couldn't figure out how to delete it myself.  I don't know what it is about this forum, but I seem to have a really difficult time with it. I thought I responded yesterday, but nope, it didn't post.

When I say that some of the ingredients settled in the throwing water, I mean immediately, and very firmly. I scooped it into the garbage for a long time because when I added it to the reclaim, I got big clumps of dried material that did not blend in. In the future, however, I'm hopeful that a small amount of vinegar in the throwing water will keep these materials in suspension long enough to evenly distribute them in the reclaim bucket. 

I wrote to PSH to ask for advice as well. He advised against adding more bentonite, because it would increase the dry shrinkage and raise the risk of cracking. He advocated for epsom salts, again, but I had problems with my engobe and clear glaze bubbling up off the surface back when I first tried their 909 clay (which is just 910 + epsom salts).

I've already learned a lot since posting my questions a few places, so thank you all so much!

[oldlady]

can you describe exactly what you do to reclaim your clay?   you say you get dry clumps from your throwing water.

  my method of reclaiming any clay is to let it dry out in small,  thin pieces at least overnight if it is dry where you work.   i toss those dry pieces into a bucket to hold them until i am ready to pug.   the day before, i add water to about an inch above the level of dry bits.    there is no reason to hold wet clay for months, it is just not healthy as well as messy.  and hard, wet clay is a pain.

i pugged 8 buckets of reclaim last winter.   did not use all of it so i am going to pug it again soon.   i only use pugged clay to throw with, never a slab.   the clay is fine but sometimes small bubbles of air are incorporated during the pugging process.  rather not see them in a slab.  yes, i have a de-airing pugmill, it is a Bailey and works wonderfully.  

[Callie Beller Diesel]

If you ever have problems with the forum, please don’t ever hesitate to message one of the moderators! We are here in part to walk you through any or all of the vagaries of the software. You can message us (or anyone else) by clicking either on someone’s profile picture to hit the “message” button, or you can use the envelope icon at the top right of the page.

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In terms of your reclaim, some porcelains really don’t reclaim well unless you use a slurry method, and it sounds like PSH 910 is one of those. Either that, or just cut it with fresh clay as already mentioned. 

For slurry methods, you’ll have to turn your reclaim, including that sludge you’ve been discarding, and really blend it until smooth before drying it out into a workable consistency. I use a corded drill and a thinset mixing bit, but I’ve seen others advocate for pushing your slurry through a 60 mesh screen with a toilet brush. It depends on what you have to hand, or have money for.  Most people are familiar with laying slip on a plaster bat to dry it out, but if you don’t have space for plaster, you can dry it on an old sheet laid over a wire shelf.

[Megga]

Today I found several bags of clay intended for reclaim, that had been tucked under a step and forgotten about for... gosh, I've no idea how long... but YEARS. What I found very interesting was the consistency. I've seen clay dry into a solid mass before, but never anything like this. It was still damp, but had broken apart into crumbles. I think it could be an example of what I've heard about porcelains becoming thixotropic when the soda in the feldspar leaches out over time. (?) I think that's why some porcelains don't reclaim well. Or, it could be a result of freezing and thawing repeatedly. (?) Or, a combination thereof. I find it interesting, anyway. I'm trying a few different things with the bags to experiment with it.

Sorry the photo is a bit blurry, but this is what it looked like. Now That's short. 

Edited June 18, 2022 by happy_pots

[Mark C.]

Yes its the result of freezing and thawing repeatedly

 

[oldlady]

try dropping the bag onto concrete to break it up to a much smaller size.

[Callie Beller Diesel]

+1 for that being freeze/thaw cycle on clay. If it’s still wet enough, you could try and see if it’ll wedge up, but  if it doesn’t you’ll have to take it down to slurry and dry it to a working condition.