Richard Selfridge on thu 27 mar 97
Hi all again. I 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. Lots of images, fairly fast loading.
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 machines of the same
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 it is better than the
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 that 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 weigh up 10 four pound balls of pugged clay to make
large casseroles, wrap the clay tightly in plastic and then the phone rings
and a 45 minute call or a customer calls us away. We eventually throw these
balls, maybe an hour later, 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 thixotropic yield point so
that it does not seem to become more thixotropic and slump prone when you
throw it, as does the wedged clay. 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 the 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 pugmill, (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 2 cents 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/selfridg
ps. Let me know what you think of the site and how fast it loads for you.
Conceptually, it is like a retrospective exhibition or illustrated resume. I
hope it adds useful information and is visually stimulating. Carol and I
will attend our first NCECA in Las Vegas. We 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 with questions at
selfridg@compusmart.ab.ca
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