Annie Chrietzberg on sat 25 mar 06
Plaster-Casters:
A few more things I thought of at breakfast....
I don't think the mix of plaster and the water ratio would be as
critical for press-molds as it would be for slip casting molds, but
if you are having to use a releasing agent to get the clay out of the
plaster - well, it just doesn't have to be that way - so you might
try weighing your plaster and water next time & doing the 3 minute
soak & mix I outlined in my other post today, or if that doesn't work
for you, try someone else's method.
Never ever use heat to cure or to dry out a mold. It causes the
plaster to break down. Plaster does like to sit in front of a fan,
though. When you are letting a mold cure or dry, sit it up on two
sticks so the air can get underneath.
If you are making a one piece mold, the mixing of the plaster & water
isn't as critical as it would be for a two-piece mold. Once you get
into multiple pieces, though, I would think you would want each
plaster piece to have the same ratio and therefore expand at the same
rate. Myself, I also want each piece to have the same absorption
rate once it is put into use.
Clean and put your molds back together after each use. Demold
promptly. Don't let clay dry in them. Use clean water and a clean
sponge. Plaster is delicate, and the nicer you treat your molds,
the longer they will stick around. Jonathan likes to use sea
sponges, but I prefer the orangey-yellow round little synthetic
sponges - the ones that come in that first basic tool kit. I have an
idea that the sea sponges have harder areas in them, which cause
faster deterioration of the mold, and the synthetic ones do not.
They feel softer and uniform to me. This theory has not been
scientifically proven.
If there are animals around the studio - don't let them into the
plaster area. If they gets it on their feets and licks it, it ain't
gonna be good.
If you wear contacts, you really don't want plaster dust to get into
your eyes. Trust me on this, it's not comfortable. I confess that
if I'm mixing 5# or less just once I can get away with it, but if I'm
in the mold room mixing again and again, or we're mixing a whole bag,
I get out the full face respirator. And, we have a vent fan in the
mold room to remove the cloud.
I have a sneaking suspicion that I could have weighed out the water
wrong on my first pour yesterday, so I'm going to re-pour that part
now, before I remove the model, which, this time, was made out of
Klean-Klay, which is an oil-based clay.
oooooo - another tip - if you are going to use a bisque piece for a
model, do a soft bisque - like ^018. Then, soak the piece in a
bucket of diluted mold soap overnight or longer. It beats coating
and re-coating a piece of bisque that can just suck the releasing
agent right in.
later,
Annie
Ceramic Design Group
blah blah blah
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