Stuart Altmann on thu 20 nov 97
Open a 50 lb. box of clay, one that has been sitting around for a month or
so. Take out one of the two 25-lb plastic bags of clay and drop it (clay
still in bag) on a solid floor, or slam it down on your wedging table. Do
it again. Now tap the bag of clay back to its original shape. (At this
point, ideally, someone else will, out of your sight, mark each of the bags
in some cryptic way, and shuffle them.)
Now knead the clay in each of the bags, and pay attention to how easy the
clay is to work. (If your partner but not you knows which bag is which,
decide which works more easily before their identities are revealed.)
I believe that clay is easier to knead after it has been "awakened" this
way, and I would predict that you would observe the same difference if you
could get a batch fresh from the pug mill vs. the same clay after it has
been sitting around--assuming that no water has been lost.
The practical implication is clear: "wake up" you clay before wedging it.
But what is the explanation? One possibility is that the slam tends to
align the colloidal particles. Anything else? Have others had this
experience?
Stuart Altmann
Gavin Stairs on fri 21 nov 97
At 09:30 AM 20/11/97 EST, Stuart Altmann wrote:
....
>But what is the explanation? One possibility is that the slam tends to
>align the colloidal particles. ...
Not align, but rather the reverse. The slam onto the floor injects a
certain amount of energy into the clay, which eventually ends up as low
grade heat. This is essentially an increase in the energy (activity) of
the electrons and bonds in the clay elements. On the way to becoming low
grade heat, the energy tends to disorder the material. So instead of
aligning the clay particles, it tends to un-align them. This can be
thought of as a consequence of the second law of thermodynamics, or more
properly as a consequence of the statistics of random fluctuations.
Without the big words, if you shake up a tray full of ping-pong balls, you
expect them to get confused instead of all lining up in neat rows. If you
want them to be all aligned, you have to push them together with a straight
edge, or let then settle against and edge or the tray. The first is
analogous to slamming, the second to rolling or throwing. So after
throwing or rolling the clay may be more ordered than before. Wedging is
all about disordering.
Incidentally, the question of the teapot spout that unwinds, or the tile
that comes out oblong, is connected to this. If the clay is aligned, it
will have anisotropic properties, which simply means that upon drying (or
firing) it may shrink more in one axis than another. In the case of a
thrown pot it may untwist, and in the case of a tile it may shrink more one
way than the other.
Gavin
stairs@echo-on.net
http://isis.physics.utoronto.ca/
416 530 0419 (home) 416 978 2735 (work)
Toronto, Ontario, Canada
Arturo M DeVitalis on fri 21 nov 97
Found some 10 month old Cone 5 porcelen buried under some other
stuff...felt hard as a rock. Opened the bag..slammed it around with
vigor and threw pots with some wonderfully soft plastic clay...I thought
everybody knew about this old method!
David Hendley on fri 21 nov 97
When I taught beginning pottery classes in the 70's I was
inevitably asked why clay had to be kneeded before use.
My answer was that, in addition to making sure it was
well mixed, you had to "wake up" the clay
and let it know that it's time to go to work.
They bought it,
and it makes sense to me.
David Hendley
Maydelle, Texas
At 09:30 AM 11/20/97 EST, you wrote:
>----------------------------Original message----------------------------
>Open a 50 lb. box of clay, one that has been sitting around for a month or
>so. Take out one of the two 25-lb plastic bags of clay and drop it (clay
>still in bag) on a solid floor, or slam it down on your wedging table. Do
>it again. Now tap the bag of clay back to its original shape. (At this
>point, ideally, someone else will, out of your sight, mark each of the bags
>in some cryptic way, and shuffle them.)
>
>Now knead the clay in each of the bags, and pay attention to how easy the
>clay is to work. (If your partner but not you knows which bag is which,
>decide which works more easily before their identities are revealed.)
>
>I believe that clay is easier to knead after it has been "awakened" this
>way, and I would predict that you would observe the same difference if you
>could get a batch fresh from the pug mill vs. the same clay after it has
>been sitting around--assuming that no water has been lost.
>
>The practical implication is clear: "wake up" you clay before wedging it.
>But what is the explanation? One possibility is that the slam tends to
>align the colloidal particles. Anything else? Have others had this
>experience?
>
>Stuart Altmann
>
>
David Hendley
Maydelle, Texas
See David Hendley's Pottery Page at
http://www.sosis.com/hendley/david/
Louis Katz on fri 21 nov 97
=3C/NOFILL=3E
-------------------
Thixatopy.
Same reason that Gertsley Glazes gel on sitting. Wake them up and they
become more fluid. I defer to others for the technical answers, I am
not fluent in Ionic, but would like to learn.
Louis
david adam edelstein on sat 22 nov 97
On Friday, November 21, 1997 9:55 AM, David Hendley [SMTP:hendley@ns.sosis.com]
> ----------------------------Original message----------------------------
> When I taught beginning pottery classes in the 70's I was
> inevitably asked why clay had to be kneeded before use.
> My answer was that, in addition to making sure it was
> well mixed, you had to "wake up" the clay
> and let it know that it's time to go to work.
> They bought it,
> and it makes sense to me.
That's always made sense to me; both on the
spiritual-connection-to-the-clay level, and on the
more concrete level of "You're taking in a lot of
information about how the clay feels that day,
how plastic it is, etc. etc., which will inform how
you throw or work it when you're finished kneading.
In some sense you're not only waking the clay up,
you're creating and entering a creative/sacred
space in which to work, in a ritual that potters have
conducted since we first got clay on our clothes.
aloha
--dae
waxing philosophical this morning in Seattle
david adam edelstein
davadam@well.com
http://www.well.com/~davadam
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