So I got some materials online, a (mostly) willing volunteer, and some helpers, and we set about things.
I got a lot of help from this instructable, but we modified the process enough that I think it deserves its own step-by-step.
Why did I want a cast of my face? It will all be explained in time. But rest assured, I have further plans for it.
Step 1: Materials
plastercloth (it comes in rolls- get a couple of rolls)
alginate* (a 1lb jar of dermagel is plenty for casting a face or two)
plaster powder (I used something like three cups per face? I didn't really measure.)
the above things can be bought at Douglas and Sturgess online.
a mixing vessel- I used a biggish yogurt cup (see pictures later)
scissors you don't care too much about
a cardboard box or sheet of cardboard
ideally, a box-cutting knife (for cutting the cardboard)
a shirt you don't mind ruining (to wear while getting your face cast)
a couple of bowls for water
*A note on the alginate: I've plaster cast my face and those of others before, but I always just used plastercloth with some Vaseline on the eyebrows. So why use alginate? Two good reasons. Firstly, the internet now warns me that people have lost bits of themselves to plaster molding themselves- plaster heats as it sets, and can get quite warm. It can burn you right to pieces, apparently. I think this is more of an issue if you're pouring mounds of plaster on something that if you're just using plastercloth, but good to keep in mind. The second reason is more important to me: you get wonderful detail with the alginate. Plastercloth is going to make you a mask that fits nicely to your face. Alginate is going to give you a mold that really looks like you.
Step 2: Prepare workspace
Pre-cut some strips of plastercloth.
Put some water in bowls so that you'll be prepared when it's plastering time.
Step 3: Cut cardboard splash guard
Basically, cut a hole in the shape of your face. This will define the edge of your mask. Start by cutting your hole too small, then work it out bigger and bigger until you fit in snugly and are satisfied.
I highly recommend leaving a cardboard bib to cover your body.
In the pictures, I struggle to size my face guard. Kiteman demonstrates proper guard-wearing technique.
Step 4: Prepare subject
Have them lie down on the prepared newspaper surface. Make sure they're comfortable; they'll be there a while.
Put Vaseline on any hairy bits: eyebrows, eyelashes, beard if that's an issue for you.
Also put Vaseline around the edges of the cardboard, to seal it.
Put straws in their mouth (and possibly their nostrils, as demonstrated by Conker-X). The straws are for breathing, so make sure they will be comfortable breathing ONLY through the straws.
Step 5: Mix & apply alginate
You should mix it to the approximate thickness of porridge. Or, that's what Kiteman and Conker-X said. I'm American, so I went for a Malt-O-Meal type of consistency, or a little thinner.
Try pouring some on your subject's face. If it drips right off, it's too thin. If it globs up, it's too thick.
Carefully pour and glop the mixture onto the subject's face. Advise the subject to be calm and breathe deeply through the straws. There is a bit of a panic response when your nose and mouth are both covered, and it can be instinctive to inhale through your nose. Don't do that! Be calm. DO NOT ACCIDENTALLY POUR ALGINATE INTO THE STRAWS.
Since the alginate is a bit runny, it will tend to gloop down off of the face, particularly the nose. Just push it right back onto the face where it needs to go.
It sets pretty fast.
Step 6: Apply plaster
This part is really easy. Just take your cut strips of plaster, dip them in the bowls of water, and apply them to the face.
The point of this is to provide a rigid form for the alginate once it comes off of your face. My plaster-face was pretty thick; from the inside, it felt like I had about an inch of stuff on my face. This was probably more plaster than was strictly necessary.
Step 7: Let it harden
Step 8: Alternate methods 1: squash your face
We used Conker-X as a guinea pig, before we figured out the splash guard and how alginate should be used. So unfortunately, his alginate mold didn't turn out too well. And we were out of plastercloth. But we already had a plaster in the shape of his face, so we thought of a couple of ways to use it:
- Stick breathing straws through the plaster
- Carefully fill plaster with alginate, avoiding straws
- Put straws in mouth
- Squish face down into alginate
- Hold it until it hardens
Step 9: Alternate methods 2: Pour-down
- Put splash guard on subject
- Put plaster mask on subject
- Duct tape effusively (subject can take a break during this step), leaving a hole at the top
- Put contraption on face
- Pour alginate into hole at top (subject may need to leave some space between face and plaster)
Step 10: Remove face
Assuming the plaster is reasonably firm, you can flip the piece over and let the plaster support the alginate.
Step 11: Set up face for plastering
Carefully set up your mold somewhere contained and supportive, e.g. on crumpled paper in a box. It should be as bowl-like as possible in order to hold the plaster.
Step 12: Mix & pour plaster
Step 13: Let it sit
Step 14: De-mold and touch up
Look, a face emerges!
There are probably a few weird bumps. For touch-ups, a file and some sharp chisels would be nice. Barring that, I used a flathead screwdriver, a rough file, and a small hex key to get into the cracks. Worked okay.