Making a silicone mask 2: Engineering the mold

When they tell that old silicone might not set, they mean it.

In this episode:

There’s many a slip twixt the yup and the ick.
Here today, goo tomorrow.
A moldmaker and her money are soon parted.

Models are easy. Molds are hard. Masks, I was discovering, are even harder. I had a model for Kat’s mask. Now I needed to figure out how to turn it into molds.

I spend almost as much time engineering a sculpture for mold-making as making the sculpture itself, so I knew the basics. I examine the sculpture for undercuts and fix those, fill in cavities that might cause casting material to get stuck inside the mold, rejigger thin tendrils that might not cast, and just generally make it as friendly as possible for making the mold, filling it, and removing the final product without breaking it.

This time is more complicated: I’m working inversely: Usually the final product is hard, brittle glass and the mold is flexible rubber. I only worry about getting an accurate rendition of the OUTside of the model.

This time my final product would be soft, flexible silicone, and the MOLD would be hard and brittle. Worse, I’d need an accurate rendition not only of the outside, but also of the INSIDE for my two-sided mask.

Further complication: The final product had to be wearable. Silicone doesn’t breathe, so it traps moisture and oils against the skin. Ever wear rubber gloves for an extended period of time? Yeah. Like that, only all over your face. We’d have to consider padding the inside slightly with a wicking material, such as cotton batting…and then make sure we could wash it.

How a mask fits is also an issue:

• If it flops around and slides all over Kat’s face, or it’s so tight it cuts off her circulation or breathing, she’s not going to be wearing it very long.
• She must be able to put it on, and take it off, which means either the mask has to flex enough for easy removal, or requires fastening apparatus that Kat can undo herself. (A mask that someone else has to remove is just asking for trouble)
• The eyeholes won’t do much good if they’re not aligned with her eyes, and the silicone over the ears shouldn’t be so thick it muffles her hearing.
• She’ll run out of oxygen pretty quickly inside a mask that blocks her nose and mouth.
• A mask that doesn’t fit (and even one that does), must move with Kat’s head. Otherwise, turning to look at something will knock the mask over vital orifices.

IOW, accurate detailing of the INSIDE of the mask is just as important as sculpting an effective exterior. It would be best to use Kat’s real head for sculpting and moldmaking, but not really practical. (I can’t get enough of her time to sit still for a couple of hours, let alone several days, and removing her head would pretty much eliminate the need for a cosplay mask).

I’ll need to make a clone of Kat’s head, AKA a “head armature,” and construct with that. This was my plan:

Hopefully, the illustration makes it easier to follow, because this is a pretty complex project. I’d start with an actual head (Kat’s), take a mold of THAT, then make what’s called a core mold, with a pipe going down the center. The pipe is flush with the top of the head, but protrudes three or four inches from the neck–that’s where we’ll pour silicone.

Once I have the core mold, I can go back to Kat’s head and start sculpting the real mask model. Once it’s finished and approved, I’ll make a second mold, this time a two-part mold of the actual mask. Both molds, as I’ve mentioned, should be rigid and NOT silicone, to avoid problems with sticking and separation.

We could save a lot of money and time using plaster of paris for these molds, but they’re heavy and fragile, hugely prone to breakage. I’ll probably make a core mold of plaster, since it can’t be hollow and hold the pipe, then make the outer shell mold in two-part resin or plastic.

That will give me a solid structure for pouring, and allow me to drill holes and screw the two masks together, essential for accurate positioning. The outer mold will be drilled again, to put bleed vents all the way up the structure. The mold is sealed at the top and essentially a closed system–silicone pours to the bottom from the pipe at the neck/top, and then rises, pushing out air.

Bleed vents serve two purposes: They provide paths for the air to escape, and they also signal when the silicone has reached a certain level, by spurting out the vent. I’ll need someone (Kat or The Resident Carpenter) standing by to help me plug the holes with soft clay or wax; otherwise the silicone will all run out on the floor. When the mask sets, I’ll take it out and finish it.

That little inner mask problem…

Plan in mind, I now needed a reasonable facsimile of Kaitlyn’s head. The process for making one is called “whole head lifecasting,” and it’s not for the faint of heart. You’re encasing your model entirely in moldmaking materials for at least 45 minutes, probably closer to a full hour. That doesn’t sound like much…until you’re breathing through straws in your nose, barely able to hear, and waiting for the getting-a-bit-hot plaster to cool down and solidify.

I’ve had battle-hardened soldier types start to crack after 30 minutes of lifecasting a FACE mold, let alone a whole head. We could save Kat the grief (and about a week of time) by using a commercial head armature.

Monstermakers sells one named Alanna for $75. Since we’d need close to $200 in materials to make a custom head armature, it seemed like a good tradeoff, so I ordered one. Commercial head armatures use average female head measurements reduced by about 5% so that, with luck, a silicone mask made with one will stretch just enough to fit over the average female’s head.

Naturally, there’s nothing average about Kat’s head. Sigh.

When Alanna-the-armature arrived, I got out the calipers and took both Alanna’s and Kat’s head measurements. Ideally, the armature’s should be 3mm-4mm smaller than Kat’s. And mostly, they were.

If Kat’s face was narrower than Alanna’s, I could pretty easily pad out the armature to the proper dimension. But where she was BIGGER than Kat, well…she’s a hard, hollow plastic shell. I couldn’t exactly carve her back. These were the measurements I got; the ones in red are where she was bigger.

The difference in nose width didn’t matter that much; Alanna doesn’t really have much of a nose and we need to leave the nose open anyway. The bigger concerns were the differences in the actual head dimensions. Alanna simply had a bigger head, which meant that the silicone mask was liable to be loose.

Hmmm. Easiest way to make sure it will fit is to make a testcap of Alanna, ending where the mask would end, let Kat try it on, and see how it fits. That will also let me check the nose and figure out how THAT will be constructed. While I’m tempted to just make a solid structure that covers the whole nose (and let Kat breathe through her mouth), that’s not very kind.

I suspect we’ll wind up making a solid nose anyway, then cut and fit to Kat exactly.

I had some leftover silicone from my last real moldmaking about 4 years ago (pre-Saving Elmo). I mixed it up, adding some test colorants, and brushed it on Alanna. Typically, you thicken silicone when brushing, but I was out of thickener. I figured I could simply push the drippy stuff back UP onto Alanna for the 10 minutes it would take to set.

Famous last words: When they tell you that old, already-opened silicone may not set, they mean it.

Two hours into pushing saggy silicone back up the model, my arms gave out. It was midnight, so I threw in the towel and went to bed. 24 hours later, Alanna was STILL dripping a giant puddle of midnight-blue silicone on the worktable.

Ever try to clean a lot of old, drippy, sticky blue and purple silicone off your model and work area? I don’t recommend it. Sigh.

Fortunately, the new silicone arrived the next day. Worked great. Mixed up a little, colored it and painted it on, let it cure, and pulled it off Alanna. Took maybe 20 minutes. Humpfh.

Choosing silicone

Anyone working in silicone will tell you there are about as many types of silicones as there are artists using them, each suited to a particular type of work. There are four properties of silicone I needed to consider:

• Shore hardness
• Work, set, and cure times
• Viscosity
• Silicone type and durability

Shore hardness determines how far a probe can push into a mass of cured silicone, and it’s a measure of the softness and elasticity of the material. It’s measured in different scales; the softest uses the ShoreA scale, and that’s what I’d use. Masks and skin prosthetics are typically made with a very soft silicone, that is, one with a ShoreA hardness less than 25 (the higher you go, the firmer the silicone). The material is extremely compressible, very elastic, and adjusts pretty easily to changes in shape.

I’d stick with somwhere between ShoreA 10 and 20, which would make the mask very stretchy, almost a tough gel, and easy to remove without tearing. The real Batman masks appear to be far more rigid, probably at least ShoreA30 or 40, but we were going for comfort.

Because we’re pouring into a double-walled mold, the silicone also needed to be on the thin, runny side to make it past narrower spots in the mold. Brick in the Yard, one of my favorite moldmaking sites (another is Smooth-On) suggested using an inexpensive power pump from the hardware store to provide extra hydraulic oooomph when pushing the silicone in.

I’d want a relatively long working time–some lifecast silicones set up in as little as 5 minutes–to prevent the silicone from solidifying before the mold was completely filled. OTOH, after pouring, it needed to set up within an hour or two. I have a pretty demanding dayjob and it’s hard to get enough time to complete a task after work–you can’t leave moldmaking materials halfway through a process.

Therefore, the mask molds would need to be completed over one weekend, and the mask made over the next. A short cure time would help me work within that 48-hour window.

There are two primary types of RTV silicone (RTV=room-temperature vulcanizing): Tin-cure and Platinum-cure. Tin-cure is (much) cheaper, but tends to shrink and deform over time. If I’m going to this much trouble, I want the bloody mask to last, so platinum it is.

Further, I want the silicone as transparent as possible, which gives me the greatest control over color depth. If I don’t want translucency or the shine of silicone, I can add “deadeners” and “opacifiers” to either the silicone or the paint to alter the final mask.

In the end, I picked a PlatSil Gel-10 silicone. It’s translucent, almost transparent at less than 1/4 inch thick, flows well, and extremely soft and flexible. It should give me some rigidity at the thick parts (around the nose and brow) but be extremely comfortable to wear. The softness should make it a tad sticky against the skin, which should help with the mask’s tendency to slide forward with the heavy jowls.

Kat is debating sewing long black hair into the back of the mask, so the low tearability and softness should help that, too. I calculated needing about 3 pounds of silicone for the entire system (you must account for the silicone in the pipe and coming out the bleed vents, too), and wound up buying 8 lbs; that should give me enough to recover from disasters.

Coloring the mask

Generally, you tint your silicone to the lightest, least textured part of your mask. Kat chose black, purple, midnight blue (and potentially a strong yellow-orange for the triangular nose), which meant that the base silicone tint would be a rather deep, cool purple.

You can mix pigment directly into translucent silicone and get a really nice, almost glowing shade; I already had a basic pigment palette that would give me every potential shade she wanted. Mica powders would saturate the color, and add depth with glittery swirls of the same tones.

I’d hold back a little bit of unmixed silicone, tinted to the purple shade, and mix it up to fill in any pinholes or gaps from the mold. Once it dried, the REAL painting would begin.

Silicone paint must be applied while the silicone hasn’t fully cured; otherwise it tends to flake off. It’s actually a type of silicone itself, and can be mixed like oil paints, then either airbrushed on or painted.

I don’t trust my airbrushing skills, so I’d be painting with a very soft brush. I can add more mica to the paint for a boost in the glitter factor. I want the black areas to be more matte and light-absorbing; there I could add black flocking–finely chopped fibers.

The mask would retain the shine of silicone. Most of the Batman and Catwoman masks have a satiny finish. We could achieve that with “deadener…” if we want it.

Engineering done. What’s next?

That’s the plan…so far. Like any project, the above is liable to change as we get into it. Next up, though: Make the core mold.