Monday, September 7, 2009

They're BaaAAAAck!

Well, the last few weeks have been nothing if not completely frustrating.

So here I am, custom orders on the go, wholesale orders on the go, desperately trying to stockpile work for upcoming Christmas shows, frantically trying to replace stock that has sold at summer shows. I'm busy. VERY busy. And I don't really have time for things to fall apart.

But alas. It had to be...

Remember that problem I was having a while back with my brand-spankin' new pug mill? Where my clay was corroding the inside of the mixing barrel and pesky little chunkies were making their way into my pieces?


The pugmill manufacturer recommended that I add epsom salts to my clay body. What this would do, I was assured, was change the pH of the clay which would in turn, prevent all those pesky little chunkies from forming in my pug mill. Okay. No problem. 44 grams, dissolved in hot water, added to 25 lbs wet clay. Mix, pug, throw.

No problem, right?

WRONG!!! What a complete disaster. Have a look for yourself:

Yup. Three kiln loads and counting. Ruined.

After much crying, cursing, Clayart-ing and phone calls, here is what I learned:

Too much epsom salt can cause blebbing. As a piece dries, the salts migrate to the area of the pot that is drying the fastest (the rim in most cases). During firing, the salts will turn to gas and generally burn off. However, if there is too much salt, and the clay begins to mature before all of the gases have escaped, you will end up with what I have in the photos. Lots and lots of little blisters, all over the rims of a couple of thousand dollars worth of pots. As my luck would have it, my clay manufacturer ALREADY adds epsom salts to their clay. So by adding more, I overloaded the clay.

So there you have it folks. My advice: talk to your clay manufacturer before adding ANYTHING to your clay body. No matter WHO told you to add it.

Aaaaaaand in addition to that...

Those f'ing chunkies are back, busily corroding away at my pug mill.


oh! And that would be the NEW version of the pug mill. The one with the corrosion-resistant coating.

Yup. My luck.


  1. I am SO sorry! That SUCKS!
    I have had trouble with clay coming from STANDARD- my 213 has pieces...pepperings of metal that must have come from a corroding pugmill, night mare with transparent/transluscent glazes... hang in...I guess!

  2. Trouble in threes, well, you've definitely had your three, I hope it improves immediately from here on!

  3. You don't get any of these effects in new batches of clay, Just the reclaim, is that correct?

  4. New batches of clay, that I don't add any epsom salts to myself, do not have this problem. Even my reclaim never had this problem, until I started adding the epsom salts - (only to find out later that the company already puts epsom salts in their clay.)

  5. It seems that you have bloat. Bloat is generally thougth to be big bubbles, but it is most often tiny, tiny bubbles.
    Epsom salts are Magnesium Sulfate, MgO is an effective flux. Overfluxing, makes the clay inherently over fired, and subsequently bloated

  6. Hey Melissa,

    Sorry to hear about the problem. The chemical solution of adding stuff to the clay is tough to manage. I would suggest that you consider a mechanical solution.

    The mechanical solution would be to create a barrier between the clay and the barrel. We have had success with PVC and HDPE plastics cut and fit into the space between the augur blade and the barrel. I am told that big pugmills have these "wear plates" as a normal design feature.

    It sounded like your pugmill manufacturer was sympathetic to the problem... ask them about some type of retro fit... pay them for it if they balk, it will pay for itself very quickly.

    In our VanHo pugmill, we found that the degradation happened at those pathways where the clay flow was forced to change direction or speed. In those zones we carved up some plastic, screwed it in place and it took care of that spot.

    The factory would be able to create this better than a tech-ie in the field because they have the tools and the templates for the barrel. They should have this as a matter of course because the nature of the cast aluminium is to degrade.