Llewellyn Kouba on tue 18 nov 03
Question: I made a plaster mold for tile (really a paver as it is 1 1/2
inch thick- approx) out of plaster and used a mold release agent to get the
plasticine model free. Maybe I would not have needed this? I have done
some reading and some texts seem to imply that one should not use a mold
release as it seals the plaster and doesn't allow it to be absorbent. Now
when I go to press or (pour) the tiles will my mold be less absorbent for
drawing the water out of the tile works etc? I have also read there are
different plaster ratio pours and I could have also used a plaster mix that
would be more absorbent but may have also affected the hardness or strength
of the working model. Mold release or not to mold release? Will I still
need to use mold release now to free the tiles as I make them (largest
9x13inches). Thank you.
Llewellyn Kouba
Abbey Pottery
Snail Scott on wed 19 nov 03
At 02:49 PM 11/18/03 -0700, you wrote:
>Question: I made a plaster mold for tile (really a paver as it is 1 1/2
>inch thick- approx) out of plaster and used a mold release agent to get the
>plasticine model free. Maybe I would not have needed this?
Plasticine does not need a mold release; that's
correct. Mold soap will do no harm to the plaster,
though, and will actually harden the contact
surface. But stay away from greasy mold releases -
they're for other (non-clay) applications.
>...I have also read there are
>different plaster ratio pours and I could have also used a plaster mix that
>would be more absorbent...
If you use #1 Pottery Plaster, it will have a good
absorbency for your purposes if mixed as suggested.
If you are using plain Plaster of Paris or Casting
Plaster, a more porous mix might be useful. But
while these subtleties matter a great deal in slip
casting, they matter hardly at all for press
molding. Don't worry about it.
-Snail
Laurie on wed 19 nov 03
Hi Llewellyn,
For plaster press molds I use either Green Soap or one of the other
soap-based releases like Pure-Lube. That way there isn't a
pore-clogging film left on the plaster. I'm not sure you need to use a
release on plasticene since it already has oil in it and I seem to
remember it was always pretty much self-releasing. I used to work as a
makeup artist and made many sets of foam and slush latex prosthetics
using plasticene and plaster molds. With slush latex (which makes a
hollow rubber prosthetic) you want to plaster to absorb the water from
the liquid latex which is poured into the mold much like ceramic slip
is. Same idea. You don't want the plaster to be "sealed", needs to be
"open". Foam latex is a different animal. In the "old days" (been out
of it for a few years and don't know if there are new technologies), it
was baked in the plaster molds in a warm oven to cure the latex. The
molds needed to have a release applied to them or the foam latex "skin"
would stick in the mold. We used to paint a very thin coat of castor
oil inside the mold and dust it with talcum powder. Sort of like
greasing and flouring a baking pan.
But that is for latex, not clay! Clay doesn't need a release agent.
Normally when enough water is absorbed by the plaster from the clay
surface you can turn it over and it will drop out of the mold. if it
doesn't, then lightly tap the back of the mold and the tile should come
out. Unless you have deep undercuts, but those should be avoided in the
original tile or you will never get a clean reproduction that doesn't
need some sort of repair where it stuck in the mold. Undercuts will not
prevent the plasticene from being removed from the mold, but remember
the clay you press in will be more rigid and the undercuts could be a
problem.
One very important thing is if you are making a multi-part mold make
sure you put the release agent wherever plaster is going to contact
plaster! Or you will never get your mold sections apart except with a
hammer.
Good luck!
Laurie
Sacramento, CA
On Tuesday, November 18, 2003, at 01:49 PM, Llewellyn Kouba wrote:
> Question: I made a plaster mold for tile (really a paver as it is 1
> 1/2
> inch thick- approx) out of plaster and used a mold release agent to
> get the
> plasticine model free. Maybe I would not have needed this? I have
> done
> some reading and some texts seem to imply that one should not use a
> mold
> release as it seals the plaster and doesn't allow it to be absorbent.
> Now
> when I go to press or (pour) the tiles will my mold be less absorbent
> for
> drawing the water out of the tile works etc? I have also read there
> are
> different plaster ratio pours and I could have also used a plaster mix
> that
> would be more absorbent but may have also affected the hardness or
> strength
> of the working model. Mold release or not to mold release? Will I
> still
> need to use mold release now to free the tiles as I make them (largest
> 9x13inches). Thank you.
> Llewellyn Kouba
> Abbey Pottery
>
> _______________________________________________________________________
> _______
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
> melpots@pclink.com.
>
Kathy Forer on wed 19 nov 03
If you're going to use Green Soap for a mold, the best way is to make a
mixture with water and apply it to the mold with an old-fashioned
shaving brush. Lather it up well, let dry and rinse well. Do it once or
twice more until the water beads off. Better than any mold release,
though it's not permanent.
Vaseline cut with kerosene is good for mold seams and other non-object
parts that need good release.
Kathy Forer
http://www.kforer.com/
| |
|
