Karen Sullivan on mon 13 aug 12
I changed the use of green soap (Murphy's)
for plaster old making when I became frustrated
with the streaks that resulted with
brushing/applying....
started using WD-40...
I could spray an even coat...
seemed much easier....
karen
JRodgers on mon 13 aug 12
Hmmm! Karen, I don't understand this. I use Humco Green Soap - actually
it's called "Tincture of Green Soap" almost every day for making molds.
Never have any troubles with it. I have used many mold releases
including most recognized mold soaps, and the Tincture of Green Soap is
my first choice.
A tincture is something dissolved in Alcohol. In this case a soft green
soap is dissolved in alcohol making it a soap solution. I buy it by the
gallon through the local pharmacy. I cut the soap to a 50-50 mix of soap
and water, which when working with it gives a nice soapy lather. With a
large natural sponge I lather up the surface with the soap and then
allow to dry but incompletely so. I then brush it out dry with a china
bristle brush. I repeat this process three times or until a drop of
water beads up like a water droplet on a waxed surface. At that point,
it is ready to receive a plaster casting. The calcium in the plastr
chemically unites with the stearate n the soap to produce a surface of
Calcium stearate. Calcium stearate is waterproof.
The plaster I use is USG #1 pottery plaster. I mix and pour according to
USG. Next I wait until the plaster begins to feel hot. The setting of
the plaster is an exothermic reaction and when it reached it peak heat I
remove the plaster cast, The reason being, the heat combined with the
excess water not being bound in hydration, softens the mold soap and
removal of the mold is very easy. If the mold is allowed to cool, the
soap hardens again and the excess water is re-absorbed, making the mold
stick very tightly to the form.
Other mold release agents can be used depending on the application and
purpose. I have used Polyease 2300 - a spray on silicon mold release,
vaseline, Murphy's Oil Soap ( not my fav) English Saddle Soap, and a few
others. I still like Tincture of Green soap the best.
If your molds must be water absorbent - then you must use a good mold
soap that will not seal the plaster surface of your mold. Tincture of
Green Soap is one of those.
John Rodgers
On 8/13/2012 12:29 PM, Karen Sullivan wrote:
> I changed the use of green soap (Murphy's)
> for plaster old making when I became frustrated
> with the streaks that resulted with
> brushing/applying....
> started using WD-40...
> I could spray an even coat...
> seemed much easier....
> karen
>
James Freeman on mon 13 aug 12
On Mon, Aug 13, 2012 at 5:59 PM, JRodgers wrote:
The calcium in the plastr
chemically unites with the stearate n the soap to produce a surface of
Calcium stearate. Calcium stearate is waterproof.
John...
Excellent and informative post. I think you just nailed the underlying
problem. A lot of folks believe that the soap itself is the parting agent,
not realizing that it is just the raw material that introduces the stearate
into the chemical reaction with the plaster surface, which as you point out
creates a layer of calcium stearate, the actual parting agent.
When I presented my last demo/workshop, one of the things I demonstrated
was how I make the sprig molds for my Industrialware from metal objects
using WD-40 as the parting agent. One of the students asked why I didn't
use mold soap, explaining that he was told it was better. I had to explain
how mold soap works, and why it only really works on plaster objects. I
believe it is a very common misconception, and the source of a lot of
problems and complaints. I think many people are simply brushing on a
layer of soap as one might brush on a layer of thinned vaseline.
All the best.
...James
James Freeman
"Talk sense to a fool, and he calls you foolish."
-Euripides
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JRodgers on mon 13 aug 12
James, I agree. It simply doesn't work. The soap must be worked on the
surface (sponge seems to work best) to get sufficient interaction
between the calcium particles and the soap itself. Doing this three
times and brushing dry in between seems sufficient to get the job done.
In all likelihood, the first application of the soap provides enough
stearate to make the calcium-stearate bond. Anything after just fills
any gaps that may have occurred as well as builds the soap separation layer=
.
The formation of the calcium stearate layer works on all plasters that
I'm most famliar and comfortable with. I know what to expect from the
hydrocal, ultra-cal 30 and 60 products, and #1 pottery plaster.
With Ultracal 30, the more molds that are puled from it, the better it
gets, if it is polished with a high cotton fiber rag between each
casting. The surface becomes harder, slicker, and more impervious, takes
less soap between each setup and release is enhanced significantly. Very
nice to work with. Of course if you have some object to be molded that
has high detail or very fine detail, then it's time to move on to rubber
molds.
My experience with press molds is somewhat limited, but the few I have
made were of the #1 pottery plaster for the purposes of getting a good
release. The plaster pulls the water nicely from the clay to get a good
release. No vaseline, oils, WD-40 of the like is necessary for what I
do. Just the typical plaster/clay relationship. There is one exception.
I have a special stamp made of steel that has fine detail. I press that
into the clay and I MUST use WD-40 or it will stick and pull plugs out
of the clay. But that is the only thing I have that works that way. But
this brings me to a point. The white appliques for the Wedgewood
Porcelain line are all done in steel molds. I've never seen it done but
have read of it. So there are other ways to do this work.
Regards,
John
John
On 8/13/2012 7:54 PM, James Freeman wrote:
> I think many people are simply brushing on a layer of soap as one might
> brush on a layer of thinned vaseline.
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