Jump to content


  • Posts

  • Joined

  • Last visited

Posts posted by CactusPots

  1. I've been firing with the lid open about 3" until 400F.  The idea is to burn out the water and organics.  Then close the lid and fire with the top plug out.  I'm noticing pretty substantial corrosion on the one year old lid band from the exhaust out the top plug.  I suspect something like sulphur  burns out higher than 400.  Yes?  Best practice?

    What would be considered a safe ramp speed through quartz inversion?  I'm talking max size the kiln will handle.

  2. On 11/17/2019 at 8:06 AM, CactusPots said:

    Mark, your work sounds a lot like mine.  I have texture sprig attachments, added feet, joinery and  lots of (paper) slip work.   Some pieces as big as 25lbs wet.   What I have found most effective is a substantial time under plastic to equalize the moisture before drying.  Then it dries  under bath towels.  The final step is a couple of days in the sun.  Using that, this is my bisque schedule.

    40 degrees per hour to 120  3 hours

    hold 1 hour

    80 degrees per hour to 200 120-200 1hour

    hold 1 hour

    250 degrees per hour to 1000  200-1000 3.2 hours

    no hold

    300 degree per hour to 1823 (cone 06) 1000-1823 2.74 hours

    It's 5 hours from start to closing the lid (propped open about 3" for burn out)

    Very close to 10 hours complete.  I don't have breakage with this routine unless I miss guess how long a piece is in any phase.  It seems to me this is the best compromise between too slow and too fast.



    But now that I'm trying larger pots, I'm seeing what I'm told are quartz inversion cracks and now I realize, I'm doing 300 an hour through QI.  Also, that the overall firing is too slow and I'm wasting time (money) at the lower temps.  There are 3 or 4 cracks running up the side wall of this wide low planter.

    Also, this pot is almost the full width of the 23" electric kiln shelf, I'm making a deal on a reconditioned 1227 Skutt.  I'm told the larger kiln will be kinder to bigger pots like this.

    Here's something I don't understand.  If I add up the times on the schedule I have listed, it comes to 12 hours.  The actual firing time is very consistent at 9.5 hours.  What am I missing?


    Quartz crack resize.jpg

    quartz crack 2 resize.jpg

  3. I reused the bags the new clay came in.  Both for scrap collection and wetting and once it's pugged.   I recycle the ties from lettuce for a better twist tie than comes with the clay bag.  I have tortoises, so I have lots of lettuce ties.

    I think the best way to use recycle is to pug it wet and store it for at least 3-4 months.  Naturally, it will dry out a little, but it usually seems to hit the mark for being softer and better throwing than commercial.

    Speckled Buff and B Mix are really different and  should be a pretty interesting combination.  The B Mix is like half porcelain, right?  You could probably find a specific use for the new clay.  I have friends who desperately want my recycle, but I'm loving throwing a whole bag 20lbs.  So much better than commercial.

    The Peter Pugger seems to perfectly keep the main mixer moist, no matter how long.  Have not tried it for years.  The vacuum chamber part will dry out, so there's that.

  4. I've never made pots like these before.  I'm not the guy who makes the same stuff over and over.  My primary goal is to keep myself entertained, not pay the mortgage, so there's always a level of uncertainty.  I don't like failure any more than anyone, but I do like to keep challenging myself.   So I'm just trying to learn from advice as opposed to trial and error.  Not sure where the "waster" concept fits for me.

    My drying process is initial slow drying in garbage bags, on paper initially, then on non stick bats.  Plexiglas or masonite.    Turned inside out daily.  Then dried under towels.  Finish in the (right now really hot) sun.  One of the 2 in the pictures is thrown and the other is handbuilt.  The thrown is going to have fatter "cheeks" otherwise fairly uniform.  All construction, whether added feet for thrown (Soldate 60) or the totality of the hand built (recycle about 20lbs)   is done as wet clay as possible.  The handbuilt is done on a hump mold in one session.  Body---feet---rim.

    I did really poorly with the last "large" pots.  2 piece thrown.  So these are different methods.  We'll see.

  5. Will this be the largest span you've done?

    Since my shelves are 19" square, these pots will just about fill it up.  I can't remember anything bigger.

    Every crack tells a story.  Mostly, I think mine are forming and drying issues and not so much feet sticking to shelves.  Also, I think the bonded silicon carbide and the advancers don't tend to stick to stoneware.  What I was asking about is mostly concerning the 12" expanse of the bottom

    Isn't the largest shrinkage from wet to bone dry or maybe leather hard?  I should do some measurement tiles to see when the largest shrinkage occurs.  I'm aware that not allowing movement in an early stage could set up a crack in a firing.  You'd blame the bisque, but the problem might have been caused earlier.

  6. For the pots I pictured, I'm mostly worried about the bottom cracking.  Am I supporting the feet or the bottom with the waster slab?  My thinking was a slab across the bottom either taking the feet up or  very nearly.  Not right?

    I'm mostly interested in not having problems with the bisque fire.  If the goal is just to prevent the feet from sticking, a layer of grog should do the trick.  I've been told that there isn't much shrinkage in bisque, would the waster slab be intended for glaze fire?

    Most of my pots (probably not these) get cookies of sliced soft brick under each foot.  Mostly because of running glazes rather than cracking. If it comes out of the bisque perfect, it will usually come out of the glaze perfect.


  7. It was suggested here that I use a waster slab underneath to support the bottom of pots like these.  The space between the feet is almost 12" and 1 1/2 " deep.  A solid piece of clay like that might be 10 lbs or more and particularly difficult to dry thoroughly.   Maybe something like a trivet?  Quarter inch slab with lots of little feet?  Or maybe just lots of inch and a half blocks?

    I don't think I've ever heard of a waster slab before.

    waster resize.jpg

  8. My observation on my pugmill is that it needs to be very full to work correctly.  The best way to recycle clay is to mix scraps much wetter than you can work.  I collect scraps in clay bags and add enough water to get the desired softness.  Very soft.  Then let the soft clay age for a least a couple of months.  Getting all the air pockets out can be work in my pug mill as it holds more than 40 lbs.  I use an inch and a half delrin rod to push the clay into the corners.  The delrin is the best material I have found as it neither splinters nor mars the aluminum.   

    The result is the best throwing clay I have.

  9. Minimizing and recovering from various kinds of problems are skill sets each potter has to develop.  Some of it has to do with what kind of work you are making and where the potentials for problems lie.  I agree some work is best discarded out of hand, especially in the bisqued state.  Glaze load space is just too precious to run a 50/50 gamble.  If I try to fix a bisqued piece, I usually rebisque it to see how the fix took.

     Personally, I'm a fan of paper slip and can fix almost anything in the green ware state.  Not that I always do, because that clay is recyclable.  I advise attempting to repair just for the experience gained.  You won't know how or when to fix things until you try and fail a few times.

  10. 19 hours ago, Bill Kielb said:

    Just a quick caution
    Fans work, but we always caution their use in a studio for dust reasons as well as sweeping vs. wet mopping.

    I'm really fortunate to have my studio mostly outside because of where I live.  Air flow is my dust control.  If you live where the climate is not so hospitable,  artificially controlling dust, temperature, humidity is considerably more difficult, I'm sure.

  11. Kind of depends on what all you use the work table for.  I think the assumption everyone is making is mostly wedging.  If you want to pull moisture out of clay for any of several reasons, I like a poured plaster.  If you use more than one color clay, 2 different canvas covers works nice.  One can be mounted permanently and the other is on a removable frame.  A little bit of a building project, but it certainly doesn't wear out if done well.  Yeah, very heavy.

    My newest work table is the 6ft  run off for the slab roller.  Formica over plywood.  Mostly for assembling handbuilt.  Sometimes on a banding wheel.  Very versatile, very useful. 

    One criteria is whether the surface is going to add unwanted texture to the clay.  Another is whether reasonably soft clay will stick or not.

  12. Nerd's assumption seems to be that the fines are missing from the recycle.  That can't be the case for me.  Most of my recycle is trimming due to my throwing an extra thick bottom and trimming the feet in.  That part of the clay is hardly touched.   I guess there isn't much call for this product if it's not available from our regular suppliers.  Industrial supply usually means industrial quantities.  I am fascinated by contemporary industrial ceramic magic.  I wish more of it was readily available. 

  13. So after Min mentioned Additive A in the post on pugmills, I found this post.   No one actually responded positively to the original question here.  Since the post is 3 years old, maybe that has changed.  I can't find any pottery dealer listing Additive A.  I think Laguna and Bailey are the biggest.    It seems to be an industry ingredient that did not make it's way into our food supply.  Internet search turned it up all right.  $75 for 50lb bag.  Not what I had in mind.

    It does seem to me like it would be useful in recycling clay.  I find the stoneware I use is definitely short if I don't pug wet and age.

  14. 1 hour ago, neilestrick said:

    I agree that it's worth investigating having it repaired. It would likely be a lot cheaper than buying a whole new machine. However I think the PP design is better since it's made for mixing as well as pugging.

    Make it salable at least if you do decide to go to another make.

  15. 2 hours ago, Min said:

    Aluminium corrodes because of the ph of the porcelain, it's more alkaline than most stonewares. PeterPugger has an explanation of it here.

    When I talked with Jim Bailey a few years ago he said they are seeing pitting of aluminum pugger barrels with some white stonewares and low fire high talc bodies also. About 15 years ago before PeterPugger came out with the stainless barrels I had a friend with one of the aluminum ones and using porcelain. It's not just the pitting that was happening but little hard nodules would get pugged into the clay. I'm assuming these were a combination of alumina from the barrel plus whatever it was reacting with in the clay. They could be felt in the clay, and left bumps in the fired pots. Some people tried lining the aluminum barrel with epoxy, didn't work. I seem to remember this is the issue that started the stainless pugger market. Some claybodies are going to produce more of the pitting and nodules than others, plus leaving the clay in the pugger without using it, plus how much clay stays on the walls of the machine without getting churned into the pugged clay. Pitting isn't going to effect the clay, the nodules that can form does.

    I have heard somewhere that some porcelains have an organic component that aids plasticity.  Do you have any knowledge of this?

  16. Mark and I both have PP VPM 30.  Although, I wouldn't be surprised if he didn't have another as well.  :)

    No one knows why porcelain will degrade aluminum and contaminate the clay?  I guess it's just one of those "conventional wisdom" things that sells the more expensive machine.  My general experience is that aluminum is not all that easily corroded.  

    Like I said, Shimpo is feeding a line of BS when they contradict the fact that no one ever regularly cleans a clay pugging machine.  I'd be willing to bet Imerys, Laguna or any other manufacturer of porcelain does not regularly empty and clean their pug mills.  I would be interested to know their commercial large scale pug mills are also stainless for porcelain.  

  17. 3 hours ago, Ipek Kotan said:

    Thanks, I did. They told me it's out of warranty (7 years old) so that I should just buy a new upper barrel... They also told me that I should not have left porcelain in the machine, that I should have opened and cleaned it between uses, ideally every 2-4 weeks. 

    What exactly (theoretically) would cause porcelain to be corrosive to stainless steel?  I understand there are varying qualities of stainless and that it is only stainLESS,  but really, is there a PH cause or something else?  Why doesn't stoneware (or earthenware) have this quality?

  18. Is there any corrosion on the matching part of the barrel?  The picture basically shows half of the barrel, I believe.  The other half should mate with the machined surface in the picture.  If there's nothing more than discoloration on the matching surface, it would point even more strongly to an inclusion in the casting, I would say.

  19. 18 hours ago, CactusPots said:

    The arrows pointing to 1 and 2 are separate pieces of metal or machined from one piece?  They should be one piece, but if you're questioning the seal across the machined surface of 2, I don't see how you're saying this problem was caused.  A failure of gasket or seal across the machined surface should cause a failure on the machined surface of 2, I would think.  I'm thinking an expert machinist or metallurgist opinion would point to a manufacturing flaw.  That's really a localized corrosion. 

    I'm thinking the fix is going to be either a replacement part or grinding out the corrosion and refilling and machine work.  Expensive either way, but Shimpo's "clean every time you use it" is not the industry standard for pugmills.  I don't use porcelain, so maybe someone else has a contrary opinion.    If you can bring expert opinion to Shimpo's attention, they may reconsider their position.  Them replacing the part would be the best case.

    resize Shimpo.jpg

    If this is like my Peter Pugger, this is a one piece cast part.  The #2 surface is then machined into the casting.  I'm wondering if some type of rustable inclusion would have caused the initial oxidation, kind of like a flux.  Since the corrosion is so localized I don't see how anything inside the machine could have caused it naturally.  I also don't understand the part of our conversation about the seal.  If there was an issue there, the pressure of the clay would cause either a seal or a leak.

    Shimpo's advice to clean and empty the machine is a joke.  That would be like telling you to drain the gas from your car if it's going to sit for a month.  5 years, maybe.  

    I bet you could get some expert advice by calling Peter Pugger.  They would be what the lawyers call a hostile witness, but expert none the less.

  • Create New...

Important Information

By using this site, you agree to our Terms of Use.