Laurie on sun 8 apr 12
Back in my past career doing stage makeup I cast many an actor's face using
alginate. These were always backed up with a mother mold of plaster bandage=
s. I
always purposely made knobs and nodules of alginate on the outside to give =
the
plaster something to hang onto, but faces are relatively small compared to
bellys, so that wasn't a huge problem. One trick I always heard to make the
alginate and plaster stick together was to put strips of terry towel on the
alginate before it completely set up and someone even suggested using somet=
hing
like denture adhesive between the two if the alginate started to pull away =
from
the plaster bandage after it had set up. I used to cast whole heads using
alginate and plaster bandage two part molds and never really had a problem =
with
things coming apart where they weren't supposed to. A handy thing to have (=
if
they still make them) are hair clips, what we used to call "clippies" to ke=
ep
the edges together. Usually just keeping the outer edges together is enough=
.
Pour the plaster positive right away before the alginate starts to shrink a=
nd
make sure the mother mold is well supported in a nest of towels or somethin=
g
similar like packing peanuts (not the dissolving kind). And once you got yo=
ur
plaster positive you could carefully peel off the alginate and set it aside=
to
dry out and shrink and cast some real fun "shrunken heads" the next day unt=
il
the alginate tore to pieces.
We never liked using plaster to cast the faces directly because plaster was
heavy enough to distort features. Important when making thin old-age
prosthetics, but probably not so important when casting a belly.
Good luck,
Laurie in Sacramento
________________________________
From: Jeff Longtin
To: Clayart@LSV.CERAMICS.ORG
Sent: Sun, April 8, 2012 6:03:01 PM
Subject: Re: Bellying casting/belly casting
I've made face molds with both plaster and alginate. The alginate is best,
of course, but it tears easily. As a pregnant belly is not small my main
concern is removing it without damage.
Jeff Longtin on sun 8 apr 12
I've made face molds with both plaster and alginate. The alginate is best,
of course, but it tears easily. As a pregnant belly is not small my main
concern is removing it without damage.
My plan is to back it with a plaster mother mold. Alginate molds are
usually not backed with a mother mold but in this instance I think it would=
be
necessary.
The question is how to make an alginate inner mold with a plaster outer
(mother) mold.
There is also a non toxic rubber medium now available. I'm wondering if
that might be a better medium to use in this situation?
Thanks
Jeff
Snail Scott on tue 10 apr 12
On Apr 8, 2012, at 8:03 PM, Jeff Longtin wrote:
> The question is how to make an alginate inner mold with a plaster outer
> (mother) mold...
The plaster gets laid up just as soon as the alginate is set.
I use burlap dipped in plaster to get the maximum 'build'
quickly. It does not need to be thick, since the fiber gives
it high tensile strength. Just make sure that the burlap
is totally impregnated (ha, ha) by the plaster, with no dry
patches within the weave.
A tip: large surface-area molds with minimal surface
convolution tend to curl away from their plaster backer,
so it helps to lock the mold into the backer with 'buttons'.
Make a quickie mold of clay, with divots about 3/4" to 1"
in it, noticeably undercut. Cast these and pop them out.
When making the real mold, set an array of these around
the edge of still-gooey mold material so that they stick.
When the plaster backer get made, make sure the plaster
gets around the buttons to lock the two layers together.
Note: This is SOP for rubber molds with rigid backers, and
and allows for the mold to be 'unbuttoned' from the backer,
but alginate is very fragile, so I don't recommend trying
to separate the layers.
>
> There is also a non toxic rubber medium now available. I'm wondering if
> that might be a better medium to use in this situation?
I know that several of the big mold-rubber companies
sell mixtures specifically marketed for life molds. I would
assume that they would be optimized for this sort of thing,
but I haven't used them myself.
As for harm to the fetus, lots (seriously, huge numbers) of
pregnant-women clubs/groups, etc, do these out of plaster
all the time. It's a 'thang', these days. If there were any
likelihood of harm, someone would have noticed by now.
We don't need to speculate about hazards in unknown
territory. This has been done A LOT!
-Snail
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