Diane Winters on wed 5 nov 03
Llewellyn wrote:
>I made the Cottle boards out of pressed wood with formica surface in hopes
>that my plaster won't bond to this and will also use a mold release
--------------------------
That's how I made my first cottles, and it's a great idea. However, since I
think you said you wanted to make tiles, I've got a better one. I'm a tile
maker working with open-faced press molds for tiles which range from 2x2's
to 8x8's plus some odd shapes. I replaced the cottle system with RubberMaid
containers - these serve as one-piece, flexible mold forms that require NO
cleanup and make uniformly sized squarish plaster molds, easy to stack and
store.
Here's my process. For any given tile size I have a RubberMaid (or other
quality brand) food storage container or small dishpan that's generally
rectangular and roughly 2-4 inches larger than the dimensions of my tile, so
there's at least 1-2 inches of space around the tile. I put a pencil or pen
line on the inside of the container at the level I want to pour the plaster
up to; for my relatively thin tiles I'll only fill the container about 2 to
2 1/2 inches deep with plaster.
After modeling my original in clay (I use a light colored clay body, not
plasticene) I brush the flat back of the moist clay original with water,
then place it with the design side up in the container. The added water
allows you to initially slide the model if necessary to center it in the
container, and within minutes the water is absorbed into the clay "gluing"
it into place, preventing it from moving when the plaster is poured. I
figured out this bit after watching my first tile model float upward to be
completely, irrecoverably entombed in plaster. (Adding water wouldn't work
with plasticene, but that might stick well enough in place with a little
pressure - you'd have to test this)
Then I mix my plaster and pour in the corner of the mold container, not
directly on my model, and let it rise until it hits my pencil line. I do
some periodic agitation of the container to get any entrained bubbles to
rise (I'm going to start using that alcohol technique someone suggested).
After the heat reaction is mostly over and the plaster is cooled again, I
momentarily flex the sides of the container outward a little to get a
separation from the plaster started, turn the whole thing upside down and
stuff some wadded newspaper or toweling or foam in the container between the
work table and the plaster. Then, pulling outward on one side of the
container I press down on the center of the bottom of the container until
the plaster mold falls out onto the newspaper/towel. I scrape off any
flanges of excess plaster, gently dig out the clay model with a wooden tool,
(making sure not to gouge the interior of the mold with the tool), dry the
mold and it's ready to use. Don't leave the plaster mold in the RubberMaid
container overnight or it's hard to get out (or, if you do, pour water on
top of the plaster, let it hydrate, flex the sides to let some of the water
down and then follow the mold removal procedure above [I've learned all of
my Don'ts the hard way])
Hope this helps you or someone,
Diane
in Oakland/Berkeley
Llewellyn Kouba on fri 7 nov 03
Diane,
Many Thanks to you at Oakland for all the tile helps. See what books often
don't tell you are pitfalls like > when the plaster is poured. I
figured out this bit after watching my first tile model float upward to be
completely, irrecoverably entombed in plaster.
Ouch that would be a costly boo boo and one that I would not like to
experience first hand. Can you give me a reference point for learning more
about the alcohol techniques to help out the bubbles in plaster
phenomenon. Or do you just take a stiff drink and hope it all works out. haa
Llewellyn Kouba
Abbey Pottery
At 04:50 AM 11/5/2003 -0800, you wrote:
>Llewellyn wrote:
>
> >I made the Cottle boards out of pressed wood with formica surface in hopes
> >that my plaster won't bond to this and will also use a mold release
>--------------------------
>
>That's how I made my first cottles, and it's a great idea. However, since I
>think you said you wanted to make tiles, I've got a better one. I'm a tile
>maker working with open-faced press molds for tiles which range from 2x2's
>to 8x8's plus some odd shapes. I replaced the cottle system with RubberMaid
>containers - these serve as one-piece, flexible mold forms that require NO
>cleanup and make uniformly sized squarish plaster molds, easy to stack and
>store.
>
>Here's my process. For any given tile size I have a RubberMaid (or other
>quality brand) food storage container or small dishpan that's generally
>rectangular and roughly 2-4 inches larger than the dimensions of my tile, so
>there's at least 1-2 inches of space around the tile. I put a pencil or pen
>line on the inside of the container at the level I want to pour the plaster
>up to; for my relatively thin tiles I'll only fill the container about 2 to
>2 1/2 inches deep with plaster.
>
>After modeling my original in clay (I use a light colored clay body, not
>plasticene) I brush the flat back of the moist clay original with water,
>then place it with the design side up in the container. The added water
>allows you to initially slide the model if necessary to center it in the
>container, and within minutes the water is absorbed into the clay "gluing"
>it into place, preventing it from moving when the plaster is poured. I
>figured out this bit after watching my first tile model float upward to be
>completely, irrecoverably entombed in plaster. (Adding water wouldn't work
>with plasticene, but that might stick well enough in place with a little
>pressure - you'd have to test this)
>
>Then I mix my plaster and pour in the corner of the mold container, not
>directly on my model, and let it rise until it hits my pencil line. I do
>some periodic agitation of the container to get any entrained bubbles to
>rise (I'm going to start using that alcohol technique someone suggested).
>After the heat reaction is mostly over and the plaster is cooled again, I
>momentarily flex the sides of the container outward a little to get a
>separation from the plaster started, turn the whole thing upside down and
>stuff some wadded newspaper or toweling or foam in the container between the
>work table and the plaster. Then, pulling outward on one side of the
>container I press down on the center of the bottom of the container until
>the plaster mold falls out onto the newspaper/towel. I scrape off any
>flanges of excess plaster, gently dig out the clay model with a wooden tool,
>(making sure not to gouge the interior of the mold with the tool), dry the
>mold and it's ready to use. Don't leave the plaster mold in the RubberMaid
>container overnight or it's hard to get out (or, if you do, pour water on
>top of the plaster, let it hydrate, flex the sides to let some of the water
>down and then follow the mold removal procedure above [I've learned all of
>my Don'ts the hard way])
>
>Hope this helps you or someone,
>Diane
>in Oakland/Berkeley
>
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