[Clayart] Ivor's proposal

Vince Pitelka vpitelka at dtccom.net
Sun Mar 23 08:38:49 EDT 2014


Douglas Fur wrote:
"How do my other design assumptions sound? Specifically, that there is no
shrinkage between black hard and bone dry.
I've measured this casually and it seems to be so. What's your experience
been?"

Hi Douglas - 
We just had an experience with this. My intro students do life-size
head-and-shoulders busts, and one student did a pretty fine Medusa with hair
of snakes.  The snakes looped out from the surface - in other words, there
were loops that were attached at both ends. She dried the piece slowly under
plastic until hard-leather-hard (is that what you mean by black-hard?), and
then uncovered it.  I recommended that she paint wax resist onto all of
those loops that extended out from the surface - this is a technique we use
frequently with appendages like handles that are connected at both ends and
are problematic if they dry first. The moisture from the handle or other
connected appendage wicks into the main body of the piece and dries at the
same rate. It works amazingly well.  She did that, but missed a few. Those
ones dried before the main body, and then when the main portion dried those
loops cracked at the outside curve of the loop.

My feeling is that if you can still see some darkness from moisture, then
there HAS to be shrinkage, because the water is taking up space between
platelets. I am sure it is minimal compared to the shrinkage that takes
place earlier in the drying process, because there are water layers, which
contribute to plasticity and are responsible for the drying shrinkage, and
then there are water spaces between the irregular particles.  I suppose it
is possible that most of the "moist" color of hard-leather-hard clay is due
to the water spaces rather than layers, but I do still sense a little
shrinkage between hard-leather-hard and bone-dry.
- Vince

Vince Pitelka
Appalachian Center for Craft
Tennessee Tech University
vpitelka at dtccom.net   
http://iweb.tntech.edu/wpitelka/  





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