One of the major tools I needed for my casting supplies
is Modeling Clay, and I didn't have any until now...
A while ago I bought two 1lb packs of Crayola Modeling Clay
I was lucky to score the last two packs off the shelf at my
local CVS Pharmacy store... I paid full price for one pack ($4.99 USD)
and got the second pack for half-price ($2.49 USD)...yaaaay!
You'll also find this clay sold at Walmart, in the same aisle with the
School supplies/crafts section... yaaaay!
This clay will never dry, and is a medium density which is good for
modeling and sculpting. But it is not made for baking nor for ovens and kilns.
I use this to make a mold for rough mock prototypes by just pressing
the original object inside a slab of the clay, and gently pulling the object away
thus leaving a detailed imprint ("inwards embossed print"), and then pouring
the resin mixture into the imprint.
You must pull the object away GENTLY (do not wiggle the object out
of the imprint) or else you'll warp and bend the imprint out of shape and
your resin casting will come out warped as well.
The resin casting will result in a rough texture, but it can be sanded smooth.
A release agent for the clay mold is optional, but you can cast the resin
directly into the clay since the clay has some oily chemical composites.
Any clay residue on the resin can be cleaned off after the resin has cured
and de-molded from the clay.
You can only create a half mold with the clay; but this will also lend itself
to making a two-part silicone rubber mold by leaving the object embedded
half-way inside the clay and embedding 2 to 4 small marbles or ball bearings
inside the clay to form mold "locks", then slowly pour the silicone rubber mixture
over the object until it is covered and let it sit overnight or maximum time
for the silicone to cure.
But, FIRST, you must make a mold box around the object; and seal the bottom
edges and of the mold box down to a smooth flat surface with hot glue,
and seal the seam with clay. A strip of corrugated plastic cut to twice
the height of the object will work... bend and form the corrugated plastic
around the object, leaving some space around the object, and tape the
corrugated plastic closed and seal that seam with clay.
The mold box will keep the silicone from spilling all over the place.
Then after the silicone is cured, flip the entire mold box over and pull the clay
away from the object... then clean off any clay residue from the object,
and seal the mold box down to a flat surface again with the hot glue.
Then apply some release agent to the object and the first part silicone mold,
then pour the next batch of silicone rubber over the object and let it cure.
After the second part of the silicone rubber mold is cured, you can open the mold
and pull the object out and BAM! you'll then have your two-part mold for
casting a resin copy of the object.
I can't have enough modeling clay, for big jobs and minor jobs.
So, later this week I'll buy a couple more packs of this Crayola clay
to keep it in my stock.
Do NOT try these tips with Play-Dough, because the play-dough will
leave a powdery residue on your castings.