Hardest plaster?

Dear Orchid people–

I have a project in mind that would involve pressing thin copper
sheet into molds of various body parts, on a sculptural rather than
jewelry scale. Ideally, I would like to do the pressing with a
hydraulic press.

What I would like to know is, is there any plaster-like material
that would hold up to pressing if the casting were, say, inside a
steel form/box?

I know metal-impregnated epoxy is sometimes used this way, but the
molds I’ve seen made that way were quite small. Doing, say, a whole
hand (one side, that is) would be an awful lot of epoxy… a face
would seem out of the question, even if molded off a plaster
positive rather than a human being. Or maybe not?

Wax would be easy to shape into any mold, but I don’t want to cast
the pieces I have in mind-- I want the immediacy of working directly
in metal, if possible.

Any ideas or experiences would be very welcome. Thanks!


I don’t know if it work, but I have used rock hard water putty for
making one time use molds. I don’t know it it would stand up to the
pressure of a press. I used it with hand forming pressure only.


Hi Noel!

How about using protoplast? (or jett sett, or one of the other
thermal plastics—I simply have more experience with protoplast,
which is used in medicine for customized casts, and to help hold
things still for radiation, and more…) Protoplast is available by
the pound from aquaplast.com. I bought 10 pounds 10 years ago, and
have made many tools, molds, and jigs from it. This sounds exciting.
I’ll look forward to seeing it some day!

Cynthia Eid

Noel you might try hydrastone, a casting media for decorative
outdoor art.

Failing that I have a thought about making your die. Make the mold
of the body part out of plaster and then shoot a plaster positive
using a seperating agent. After you have the positive you can then
take a very precise impression with Protoplast, ( a plastic that
softens when placed in hot water). Use this negative protoplast
inpression with a plaster back fill in your steel box form. The
protoplast is the contact area and serves to spread the pressure more
equally over the plaster as well as provides a very durable surface
for the metal to contact. Reinforce the plaster with strips of burlap
soaked in plaster and laid up criss cross on the back of the mold,
much like laying up fiberglass.You can also use the plaster
impregnated material that the medical profession uses to make casts
for broken bones. Protoplast provides a very durable surface for
working metal I use protoplast to cover wooden forms for making
forming stakes as well as covering steel stakes to change the shape
of them. Protoplast is available at Aquaplast Corp. 1-800-526-5247. I
have also made impressions of ceramic doll head molds for casting and
the detail is quite amazing, it will even mold fingerprints. When you
are finished with the protoplast it is reusable. You just place it in
hot water and it returns to its original form. If this makes since
and you need more info or if it doesn’t make since and you need more
info you can email me at @frank_goss2 (usual disclaimer
goes here)

Frank Goss

I have a project in mind that would involve pressing thin copper
sheet into molds of various body parts, on a sculptural rather
than jewelry scale. Ideally, I would like to do the pressing with a
hydraulic press. 

I would highly recomend Devcon’s Plastic Steel Liquid (B), you can
get this in pretty large quanitities and flows extremely well. The
down side are two fold, 1) spendy, and 2) long cure time. It is used
for light duty mold making. 4 lbs will run just over $100.


I will give one bit of advice when making molds of body parts. You
might have to make the master with something that doesnt have a high
thermal reaction, like latex. Then create the pressing mold by
filling that with the epoxy. Reason being, almost all plasters and
epoxies have an exothermic reaction (ie: gives off heat). In some
instances this heat generated can be hot enough to burn the skin,
especially with large amounts of plaster/epoxy.

In anycase, good luck, sounds like a fun project.


Hi, Noel. I knew an artist once who made art nouveau and deco lamps.
For the bases he used a plaster called “Hydrocal”. I don’t know if
that’s a trade name or the type of plaster. Anyway, as he described
it, it works and feels like plaster of paris, but sets like concrete.
Actually, I Googled it since I wasn’t sure of the spelling, and it’s

Hi Noel;

Decades ago, when I was an art student, we used to use a plaster
called “Hydrostone”. It was pretty tough stuff. I don’t know if it
would work for what you want to do, but you could try it and maybe
try reinforcing it by mixing in something fibrous. First thought is
fiberglass, but it’s probaby too dangerous to work with. Maybe you
can get shredded styrene or maybe layer it with gauze.

David L. Huffman


I have not tried using any type of plaster but I have made 6" X 12"
molds using an epoxy/steel made by Anchor Seal. I have a 6" X 12"
forming box for the Bonny-Doon press. This was used to form thin
copper sheet, as I recall, about 24 ga.

Joel Schwalb


When I need to make a duplicate of something to fill in as a stone,
I make a mold out of the stuff the dentist uses for making
impressions of the mouth. The plaster is quite hard and is made to
hold form without shrinking. Metal can be worked around it, and It’s
not very expensive either. You won’t have a problem with bubbles.
The impression material is kind of rubberize and easy to work with.

Incidentally, if you’re interested, I’m busy cutting some scenic
black opal from Lightning Ridge. Got some nice pieces.

Derek Levin