(You can read How to Cast a Head: Stage 1 here.)
(This is part of the process of casting parts for Sabela, the main character of the film.)
I’ve heard a few pro puppet-makers poo-pooing Urethane foam. Apparently latex foam is far superior in its texture, density, air bubbliness, etc. But it seems like it takes months, or even years, to learn how to use it! You have to keep detailed logs on the humidity, room temperature, and how they affect the mixing times and gel quantities. You have to go through many, many trial and error batches. And with each batch you have to juggle 4-component chemical mixtures, adding each one at specific times in specific measurements. Plus 4 hours of baking time per batch! Stop motion animation takes some extreme patience, but for some reason I just don’t have the patience to be a mad scientist mixing batch after batch of noxious chemicals.
So I decided to use the inferior foam. Which, in my opinion, isn’t really that far inferior. It has its problems, but I’ve found workarounds. I’m very pleased with this technique.
The down side to urethane is that it can possibly sometimes shrivel a bit. Not sure why. Also, the bubbles are not fine enough to pick up all the details of the mold. My solution to both problems is described in the stage 1 process: line the mold with liquid latex. The details remain, the casting doesn’t shrink, and everything works out great!
So, without further ado, here is how I cast the urethane foam head for Sabela.
I use Smooth-On Flex-Foam-it! III Urethane Foam. It’s a 2-component foam that mixes in 30 seconds, pours as a gel, and foams in the mold in about 1 minute, to expand 15 times its original volume. It cures in 30 minutes. Easy! There are various densities of this foam… III is the lightest, airiest one.
To make this head, I only used 1/2 oz. of Part A and 1 oz. of Part B, mixing it vigorously in a hummus container used only for this purpose. (Clearly I eat a lot of hummus!) I also have a plastic palette knife dedicated to the purpose of mixing these components, because this stuff is messy — it sticks to everything.
There is a very small window — after the 30 seconds of mixing — to get this stuff in the mold. That window is about 20 seconds or so. I like that the foam spends its first moments as a gel so it can be poured, rather than injected. Note that the hole at the top of the mold has to be fairly wide — I had to carve this one wider, otherwise the gel would cure on its way down. It’s a 1 cm deep by 4 cm wide rectangle, approximately, carved out below the shoulders.
It rises like a soufflé… and smells somehow sweet, like mirangue.
30 minutes or so later, I peel away the foam from the outside. It is impossible to totally remove it all from the plaster, so a couple coats of release agent is a good idea for the innards of the mold, just in case any creeps in. (This happens in stage 1, of course. Hopefully I mentioned that already.) The latex lining should keep it from sticking to the inner mold, though, overall.
Carefully peel away the mold parts…
And here she is! She looks a little mottled because the latex is thicker in some areas than others… which isn’t a big deal. Once she’s painted and the seams and eyes are cleaned up, she’ll look great.
Here she is (mostly) painted and cleaned up!
* An unrelated side note: I’ve found out that this blog looks horrible on PCs. The type is ginormous and the header is too big. Sorry about that, for anyone who’s reading it on a PC… I’m not a whiz at CSS, and have no idea why it’s looking so crap. I could put “site looks great on a 1680 x 1050 monitor using Mac OSX and Firefox” at the header because that’s what I’m using but I realize that’s not practical so I’ll have to figure out how to fix it, eventually…