Working Potter on wed 6 feb 02
Good point that bears noting, the sulfur issue.It ALSO comes up in
claybodies with ingredients like the favorite goldart, too.If you do
another sculpture to be cast from clay you might want to check ou the sulfur
free clays like he ones CHAVANT carries.They have a website WWW.CHAVANT.COM
online. It has been a standard in the automotive modeling industry and
more.I have no connection other than as a customer.
Misty
In a message dated 2/6/2002 8:00:54 PM Eastern Standard Time,
snail@MINDSPRING.COM writes:
> By the way, if your plasticine contains any sulfur (as
> some of the 'old reliable' brands do, it will react
> chemically with most of the modern synthetic rubber
> compounds, and prevent them from setting properly. So
> you'd still need the ol' spray shellac. (Since you made
> you own, I'm guessing you didn't add any sulfur, but
> I don't know...what's your recipe?
>
dayton j grant on wed 6 feb 02
Hi Penny,I used to work for a bronze sculptor(Robert Graham)and theres
this light blue(about$100 a gallon) rubbery epoxy stuff (I forgot the
name but any art foundry should know of several similar products) that is
used to make very strong reusable two peice molds (for wax or plaster)no
undercuts are needed (usually) because the stuff is so elastic that you
can literally rip it out of the little corners and stuff(destroying the
original)and it faithfully holds detail as small as a fingerprint so I
guess you would make a rubber negative off of the original clay or
plastelene then you pour a rubber positive into the rubber negative (they
dont stick once one part is dry)and then you make a plaster negative that
should be pretty much clean and absorbent and since plaster wears out you
can always make more from the rubber positive.Im sure there are other
ways but thats what Ive seen so far,good luck..<8-)
d.g.
Snail Scott on wed 6 feb 02
At 12:04 PM 2/6/02 +0000, Dayton wrote:
>Hi Penny,I used to work for a bronze sculptor...theres
>this light blue (about$100 a gallon) rubbery epoxy stuff...no
>undercuts are needed...I
>guess you would make a rubber negative off of the original clay or
>plastelene then you pour a rubber positive into the rubber negative (they
>dont stick once one part is dry)and then you make a plaster negative...
I also work in bronze; the stuff Dayton refers to is
probably RTV silicone, one of many two-part 'rubber'
mold compounds. Yes, it will give very precise detail,
and is very forgiving of undercuts. But, if you are
slipcasting, your form WON'T be, so I'd try to avoid
undercuts anyway. True, the slip as it shrinks will
allow slightly deeper texture than is possible with
plaster poured into plaster. I'd try other methods of
mold-making if you really need to do a positive-negative-
positive reversal, though. ALL of the synthetic mold-
making 'rubbers' are very expensive; ($50/gal and up;)
they're designed to meet mold-pouring requirements for
foundries, including repeated pours with hot wax. If
you ever need a flexible inter-mold to make a plaster
from, try moulage or latex. They're less durable, but
cheaper for one-time use. Personally, I'd avoid the
necessity by making forms free of undercuts, and working
strictly in plaster for slip molds.
(You didn't say you had an undercut problem anyway,
did you? But I figured since Dayton brought it up,
I'd address it.)
By the way, if your plasticine contains any sulfur (as
some of the 'old reliable' brands do, it will react
chemically with most of the modern synthetic rubber
compounds, and prevent them from setting properly. So
you'd still need the ol' spray shellac. (Since you made
you own, I'm guessing you didn't add any sulfur, but
I don't know...what's your recipe?
In a nutshell: for slip molds, stick with plaster,
even if you have to do a negative-positive-negative
process to replace a contaminated negative mold. (I
sure hope you don't have to!)
-Snail
p.s. for our francophone buds: I think that in French,
'moulage' just means 'mold', but in English, it refers
to a specific type of meltable, reusable 'rubber'
mold-making compound. -S.
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