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thermal shock, now freeze /thaw

updated sun 14 apr 02


Stephani Stephenson on sat 13 apr 02

Vince, Snail and all
I was just reading some of Ted Randall's comments on his experiments
with testing freeze/thaw.
He did a test whereby he weighed a piece of fired clay, then soaked
it for a set period of time, weighed it again and got the % absorption.
He then boiled a piece of fired clay and compared wet and dry weights. I
believe he then arrived at a ratio, comparing the simple soak and the
boiling water soak measurements.
Before I paraphrase too much , I need to retrieve the notes from my
studio,so I can post a more accurate reporting of his tests. This was
different than the freeze/ thaw tests I had seen before, which involved
periods of Freezer induced freezing and thawing.
The notes also describe his observations ...he seemed to indicate that a
common view at the time was that an absorption rate of less than 4% was
considered 'safe' for outdoor sculpture in northern climates. He in
fact disagreed with that premise and describes quite well the view
that what is important is that the claybody have a certain porosity,
sufficient 'capillaries' for freezing water to expand into as it
freezes....I think Paul Lewing has also alluded to this in earlier

Of key importance is the design of your work. In designing outdoor
work , I would think about how water collects, and /or is drained or
shed from the work, and also think about the base and if/how it comes
into contact with the ground.
Also when dealing with a glazed surface, questions of glaze fit,
porosity are also factors , along with questions about clay body.

But this brings to mind another question.
What about sealants? Do you use them Snail? anyone else???
I apply a professional grade penetrating sealant (such as 511) on tile
and sculpture , indoor and outdoor.....the sealants made today are quite
amazing. Yet by using a sealant I suppose I am sealing and clogging all
those wonderful capillaries??!!! Also it would be interesting to
compare the results over time. Of course I am working at cone 04-02, not
cone 10, and glazes are satin mattes/semi mattes.
As Snail indicated though, over time even mountains will crumble...
that's how we get our lovely clay to begin with, (though we do try to
launch our babies with the best odds we can give them!)

I left many sculptures, outdoors all year for 9 years in Montana
(unsealed, some glazed, some unglazed cone 06 to cone 10 ). They really
did not deteriorate, though I rather enjoyed watching some of them get
claimed by spiders and sometimes seeds and moss would sprout in a
crevice where wind blown soil had collected

Yet the bar is set a bit higher when one is selling work to be
installed. I still shy away from recommending Alchemie and my own tile
and sculpture for certain types of exterior use in northern climates,
especially in such projects as outdoor walkways, wall caps,
basins....though it is appropriate for walls, vertical surfaces,
protected areas, pools, floors, showers etc., where water accumulation
and freeze/thaw is not a factor.

My own hope is that someday my outdoor sculptures are as gloriously
aged and weathered as the ancient brick and clay of old castles and
pueblos and other relics of bygone times. Gently fade back into the
landscape, surrender to the vines and the roots and the heaving of the
earth. Of course I want to give the customeras well as the sculpture a
few good decades before this begins to happen!!!!!

Stephani Stephenson
Carlsbad CA