August 28, 2013

So, if a picture is worth a thousand words, let's see how many words this
takes me...

There are two different kinds of vacuum thermo-forming systems. I have chosen
the "negative-mold" kind, for various reasons that I won't go into here. There
are several major parts to our mask-making system:

1) Sheets of thin thermo-formable plastic. These are what get transformed into
the masks. They are 12 inches square. They are about as thick as a business
card. They could be clear, white, or colored. We (or the recipients) could
color them with markers, paint, sequins, etc. -- just like the traditional "Dia
de los Muertos" sugar skulls that I made with my family while my son was in
elementary school.

2) A solid sculpture of the mask. I call this the "positive mold".

It's like the front half of a bust, from the temples just forward of the ears,
to the tip of the nose; and from the chin to the top of the head.

It's life-sized. So we need to size it for our intended audience: Little kids,
not "grups".

The equipment will allow a sculpture that is up to ten inches tall, up to ten
inches wide, and up to six inches deep. Maybe we could sculpt two or three
half-masks, separated by one-inch gaps, that would all fit into that 10 x 10
space; then we could make two or three half-masks from each sheet of plastic.

It can't have any "undercuts" or "overhangs", which means that a witch's long
drooping nose would not be possible; nor would the Red Skull's hollow temples
(because his eye socket ridges stick out beyond his temples).

The sculpture has to be solid, because it's going to get smothered with heavy
Plaster of Paris. So papier-mache or eggshell-thin clay won't work, unless
we fill it up with something solid such as more Plaster of Paris.

The sculpture can't be valuable, for two reasons: First, we will smear Vaseline
all over it, so that it doesn't stick to other parts of the equipment; and
second, we might have to break it apart as part of the process.

Having seen what Jeff can do with modeling clay, I would recommend that he
"simply" (hah!) sculpt the positive mold out of modeling clay.

And finally, the sculpture can't be very heat-sensitive, because during the
process it will get heated up a bit. So, before anybody spends a lot of time
and effort on sculpting a masterpiece out of modeling clay, tofu, mashed
potatoes (remember "Close Encounters"?), or whatever, we need to test the
process on a sample.

3) A set of wooden frames, used in casting the next piece, which is...

4) A negative mold. This is the tricky bit.

It takes a couple of days to make this negative mold, after we make the
positive mold. No last-minute designs! Do it as soon as possible, in case there
are any problems!

Basically, when done the negative mold will be a large block of Plaster of Paris
(actually, we'll use something similar but stronger). There will be a
depression in one of its faces, and that depression will exactly match the
shape of the positive mold.

In order to make the negative mold with its depression, we'll put the positive
mold into the wooden frame, smear Vaseline all over it, and pour in Plaster of
Paris. Once that hardens, we'll either lift the positive mold out and set it
aside reverently, or break it apart with a lot of cursing, or scoop it out with
our fingers... depending upon how it was made.

Then we'll drill a few tiny holes into the negative mold, from the
deepest parts of the depression down into a hidden void inside the block.
We'll fit a vacuum port to the block, so that we can connect the next piece
of the system to the hidden void. That next piece is...

5) A vacuum pump. This doesn't have to be very big or high-quality. One of you
(I think it was Nicholas) has already volunteered to donate a floor-style
bicycle pump for me to hack into a vacuum pump.

6) A heater. You have already heard rumours of the terrible thing that I am
going to do to the used toaster that I bought. the nice lady at the SPCA Thrift
Shop looked a little sad when I told her that I was going to take the toaster
apart... permanently.

Anyway, the heating elements of the toaster will soften the plastic sheet
(which will have been clamped to the negative mold) and then the vacuum pump
will suck the air out from between the plastic sheet and the depression, via
the tiny holes, the hidden void, and the vacuum fitting.

That will let normal atmospheric air pressure push the hot, softened plastic
sheet down into the negative mold. When the hot plastic hits the cold mold, it
will cool into a shape like the original positive mold: a mask. We'll pull the
mask out of the negative mold, trim away the excess plastic, and cut in
eyeholes and nose vents so that the little ones can see and breathe. And we'll
attach some elastic so that the masks stay on their heads.

And that will be that.

-- Tim F