Richard Selfridge on wed 26 mar 97
Hi all again, Thought I might add to or maybe confuse Gavin's great post
of last week on this subject of pugged clay vs. hand wedging. Also I ask
you to have a look at our new Web site about our Majolica, woodfired
stoneware and a "Short Stories" article about our methods and the work of
Raymond Carver. http://www.compusmart.ab.ca/selfridg
We have had a 4in. Venco pugmill since about 1981. It is a great machine
and has given us great service. Harry Davis was in fact the designer of it
and the folks in Australia even gave him some royalties for it for a while,
(unlike someone who copied and sold the design in New Zealand or so he told
Carol and I when we stayed with him there in 1980). He maintained that the
vacuum helped with both plasticity and workability. I have found that the
aged clay fresh from the pugmill is the best, most responsive clay for
throwing. I think better than wedged clay.
All the things that make me say this are in the form of hunches and I'm
looking more for consensual validation or disconfirmation than stating the
last word. Most clays are somewhat thixotropic (property of clay
suspensions to stiffen to a jelly-like mass if left to stand for several
days. Usually it will become liquid again if stirred thoroughly.The
mechanism of thixotropy is still not fully known) Cardew p. 326 1969. We
experience this when we hand wedge up 10 four pound balls of clay to make
large casseroles, wrap the clay tightly in plastic and then the phone rings
and a 45 min call or a customer calls us away. We eventually throw these
balls but those casseroles just don't have the zip. We have to put more
force on them to center and make them "yield" and when they do they are
more likely to slump and be overworked. It now takes four pulls to form
them and two "goes" to refine them instead of the usual three and one we
are used to.
Some might assume I'm just a "lazy" wedger, but I don"t think so. The pug
mill really "wrassels" the clay around, and it compresses it more than
wedging does. It takes the clay to that thixotrophic yield point so that it
does not seem to become more thixotropic and slump prone when you throw
it.We throw it fairly "soft" from the pugmill, and provided you work
quickly and don't over water it, it will, I think, make taller thinner
pots.
Because I put 1.5% neph.sy. in our wood fired body, (as a body flux which
migrates on drying to the surface it toasts up the surface and acts a bit
like flypaper to catch and hold flyash) I have found because it tends like
most soluble body fluxes to make the clay more thixotropic, this for us has
become a more significant issue. Other clays seem to have this same
property, whether "home made" as ours is or "store bought in boxes". Our
clay is blunged, power screened, and dryed up on sheets on the ground and
in bisqued "dog dish" pans for maximum particle wetting and aging before
it goes through the pug mill, (the method we adopted from Harry Davis). It
then ages for about a year ( sometimes freezing ) before it is repugged
before throwing. Yes, we have added "vinegar like" liquids in it to promote
bacterial growth. So although it is made from somewhat "short" materials
it has attained its maximum "possible" plasticity.
I think we could learn more about this complex subject, ie.exactly how
long does the clay from the pugmill "stay thixotropic", but for now that is
my .02 worth. If you wish to see some of our work over the past 25 years,
have a look at our new Web site.
Richard Selfridge.
http://www.compusmart.ab.ca/selfridge
ps. Let me know what you think of the site. Conceptually it is like a
retrospective exhibtion or illustrated resume. Carol and I will attend our
first NCECA in Las Vegas. Hope to meet some of you there. If you want to
know about a few of the things I learned while putting the site together
just e-mail me at selfridg@compusmart.ab.ca
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