Gregory F. Wandell on thu 29 may 97
Hello!
Over the weekend, I placed several (near dry) plaster stamps on the top
of my kiln to dry while firing a bisque (Cone 06). The intent was to
speed the drying process prior to carving and using. All the pieces are
now dry; however, to my dismay, the side that was in contact with the
kiln is very soft. It easily carves and crumbles with minimal pressure,
not good. Conversely, the other side is hard, not easily carved and does
not crumble, perfect.
Why did heat cause the plaster to loose its strength? Thanks in
advance!
Gregory F. Wandell
GWandell@USECRE.ORG
Bethesda, Maryland
Louis Katz on fri 30 may 97
Why did heat cause the plaster to loose its strength? Thanks in
advance!
Here is the address for a short article I wrote on Calcium, the answer is
there. The article was printed in the NCECA Journal about a year and half
ago. http://www.tamucc.edu/~lkatz/calcia.html
I am still working on a responses to all your questions for the NCECA
board. Trying to get my life back up to speed down here in S Texas.
Louis
Louis Katz
Texas A&M University Corpus Campus
lkatz@falcon.tamucc.edu
http://www.tamucc.edu/~lkatz
Bill Walker on sat 31 may 97
>Why did heat cause the plaster to loose its strength?
When you mix a batch of plaster some of the water chemically combines
with the plaster and causes it to set. If you heat the plaster to
too high a temperature, the chemically combined water is driven off
and the plaster looses its strength. The maximum safe temperature
for drying plaster to avoid driving off the chemical water is about
120F (about 50C).
Bill Walker
Alfred NY
walkerw@bigvax.alfred.edu
Joseph Herbert on sat 31 may 97
Gregory, as many others will tell you, no doubt, plaster of paris is a
HYDRATED material. The water in the plaster is chemically combined with the
other materials in the plaster and contributes to the crytals that form in
the plaster mass. Too much heat drives off the water and the part without
the water is not plaster of paris any more. the plaster power you started
with was made of calcined (heated) ingredients. You have returned part of
your stamps to that state.
Joe Herbert
JJHerb@aol.com
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