Annie Chrietzberg on sat 25 mar 06
Hey Plaster-Casters,
US Gypsum does provide information on how to use their products - all
of 'em: pottery plaster #1, hydrostone, hydrocal, etc. If you call
their customer sercice department, and ask for specific product
information regarding use of plaster for ceramics, they will send you
a packet with all the information you can eat. Be sure to request
the Volume and Mix Calculator/ Slide Rule. The calculator will take
you from measurements of the actual space you will be filling with
plaster through to the amount by weight of plaster and water you will
need. The information package will also tell you how to soak and mix
the plaster & even tips on pouring. The calculator doesn't cover
small molds, but it does cover how much water you'll need for 5# of
plaster & less. The recommended ratio for Pottery Plaster #1 in
standard application is 70% water by weight to weight of plaster.
Let me now emphasize the following: There are lots of fabulous
studio artists who have developed their own way of using the material
that works for them. Both Elenora & Notkin mix their plaster by feel
or intuition or experience or whatever you call it, and I don't argue
with the results - looking right now at the fabulous pieces of theirs
I have the good fortune to live with.
Both Jonathan and I have made molds using 100#'s of plaster per mold
piece - and we definitely follow the formula that US Gypsum provides
when mixing up two bags of plaster for a pour.
Here's some of our studio mythology: (not necessarily by the book -
this is where Jonathan's use of materials has evolved to over years,
and what we have to say about it TODAY) Set a timer for 3 minutes.
Sift the plaster into the water, let it soak till there is only a
minute and a half left on the timer. Mix untill 10 seconds are left
on the timer, let the plaster rest for those last 10 seconds to let
the bubbles rise. We try to pour over a sharp edge - he has these
little pouring things he has made from sheet metal - essentially a
pitcher spout. The sharp edge helps pop bubbles on their way into
the mold. We try not to pour the plaster directly onto the surface
of the model, because that creates a spot on the casting surface with
a different absorption rate. This can show up as what Dude calls a
hot spot that won't take glaze. Dude says, "Pour into the corner
of the mold box. Let the plaster flow up and over the piece."
Another thing we do is let the molds dry for days, or weeks if it's a
big one, before taking the first cast. Also, if a mold has sat
around for more than a day, we dip the pieces in water to get the
capillary action going before pouring. For the big molds, we use the
hose to soak it. We live in an extremely dry climate - that might
not be the thing to do elsewhere.
I just asked him about making ram dies from pottery plaster #1, and
his opinion is use the right materials for the job. Pottery plaster
#1 isn't formulated to handle 30, 60, whatever tons of pressure.
That doesn't mean you can't do it, but he says, "why take all that
time to make a ram die if you are not going to be able to get the
maximum number of presses out of it?" that being said - I know that
he has created his own personal mix of ceramical and hydrostone that
is not a recommended mix. Also, he says pottery #1 will not purge
correctly for sir release dies/molds.
Who knows? Most likely the people who actually make the materials
for industry. Since these are materials made for industry, there
will always be information available from the manufacturer. This
information is the result of scientific tests of the material, and I
personally always think that is the best place to start, and then let
your own methods develop over the years you use it in your own practice.
We currently have about 10 information packs from US Gypsum that
Jonathan gives out when he does a plaster workshop. Send me 4 bucks
to cover cost of shipping & the envelope, and I will send one to you.
Ceramic Design Group
attn: plaster caster's club
PO Box 775112
Steamboat Springs, CO 80477
As always, Jonathan is available to teach a mold making workshop at a
theatre near you. Or, if four or more of you can get together, we
can arrange a weekend workshop at CDG for our standard weekend
workshop price of $250 per person. We give good workshop - ask around.
So, it's off to the studio this Saturday morning to remove the model
from the mold I made yesterday, so it can dry & be poured Monday.
I'm working on an oil and vinegar set, and will post a picture of it
to my website when I get one finished. I'll let you know.
If you have questions/complaints about this post - please be sure to
send a copy to me off list as well, so I'm sure to get it. I'm an
archive scanner now.
best ever,
Annie
Annie Chrietzberg
Ceramic Design Group
Kitty-Wrangler - Artist - Adventurer
www.earthtoannie.com
www.ceramicdesigngroup.net
that's all folks!
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