Tweaking a Clay Body: Part One

We are going to just jump right in here. No back story, no preface. This will be part one of x number of clay tweaks I will ultimately document here. I was mixing clay today, and when I do that, I think about how I can improve my clay in some aspect. That, to me, is the whole point of doing the clay formulation in the first place. My clay is great, don’t get me wrong. It fits my glaze, allows me to do all kinds of crazy things to it, like cut it apart and stick it back together, and looks fantastic (pure white in electric firings). It is dense and vitreous at Cone 7, which is my target temperature. The one thing I would change is to make it more plastic, and usable right away, straight out of the mixer. My current clay is great, assuming it has aged for a couple months. This is the recipe starting point.

Campana White Midrange ^6-7 Ox

25 EPK
10 Tile 6
10 OM4
35 KONA F-4 Feldspar
20 Flint
3 Bentonite

Now, when I mix it, I use about 100 pounds of reclaim, and add 150 pounds of dry material. I’m usually pretty close dryness-wise and don’t need to add a lot of water, which means, I can’t blunge the bentonite. I dry mix it in. I think that the reason it needs to age, is that I need to wait around while the bentonite activates, lending plasticity. I have decided to try sourcing some more of the plasticity from the OM4 ball clay, adding it at the expense of the less plastic EPK. I estimated that 5% should be a big enough jump for me to feel the difference. I then took out 1% of the bentonite, as to not make it shrink in the drying way too much. So the new version is:

Campana White Midrange v2 ^6-7 Ox

20 EPK
10 6-Tile
15 OM4
35 Kona F-4 Feldspar
20 Flint
2 Bentonite

So far, it feels good. I did the coil-around-the-finger test, and it passed with flying colors. A coil the thickness of my finger wrapped completely around my finger without cracking, fresh from the mixer! I will put it to the real test as soon as I run myself out of the old stuff.

The worries here would be:

  • That the shrinkage has increased and will crack my pots apart in the drying.
  • That the addition of OM4 will make it slighlty yellow and riun the pretty bright glazes I have
  • That the glaze somehow doesn’t fit anymore.

These sorts of risks are worth it, in my opinion. Nothing ventured, nothing gained!



Comments

  1. Mickey says:
    February 10, 2009 at 2:42 pm

    I have aged clay nicely with yogurt if you can believe it!
    I think it is the enzymes in there chewing stuff up and spitting it out broken down that much faster. Probiotic organic is the best so far…the one with the Jersey cow lookin’ all sweet and grass fed…
    I have heard of some using beer. That seems kind of a waste to me though. :)

    Good luck with the new batch of clay!
    Exciting.
    Mickey S from
    Studio Terrafemina
    on Vancouver Island.

  2. Jeff Campana says:
    February 13, 2009 at 10:59 am

    I like my clay to smell like clay, as opposed to feces, rotting milk, or rancid beer, though.

  3. Lann says:
    March 21, 2009 at 10:02 am

    Yeah I have just tried adding yogurt a few week ago to my clay and I’m starting to think that’s a mistake. It smells bad but has been getting better then when I first put it in. I make sure to open the container for a bit everyday to let go of the methane gas that is caused by spoiled dairy.

  4. Jeff Campana says:
    March 21, 2009 at 10:51 am

    This stuff was even shorter than the previous stuff, pulling handles is a nightmare. Next batch, I will try adding some Veegum-T and see if that helps.

  5. bob says:
    July 22, 2009 at 4:00 pm

    first of all; nice use of line and glazes on your pots. after seeing your clay body recipe,I’m wondering why you have so much EPK in your body if you want it more plastic. I understand the whiteness part,but it isn’t very plastic. have you tried more of the 6-tile clay instead? just curious; also alot of feldspar,but if it works for you that’s all that matters. wonderful pots,nice forms and the incised lines move ones eye all over them. keep up the great work.

  6. Tweaking a Clay Body: Part Two says:
    July 26, 2009 at 6:11 pm

    […] down-to-the-molecular-level control of my work. The reasons for this are many. If you recall from Tweaking a Clay Body Part One, The main concern is that my clay body was just fine back when I had access to a pugmill. Pugmills […]

  7. Clay Body Revisited | Jeff Campana says:
    February 19, 2011 at 8:31 am

    […] my starting point was the old recipe I posted a long time ago here. I then made some initial substitutions based on a little research and some recommendations from […]

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