Current iteration, as of this writing–subtler ridges, whisker-like set of front nose indentation, and better ear integration.

In THIS episode of Making a Silicone Mask: The Rules of Moldmaking

  • #1: The simpler, the better. The fewer stages and components required to create your mold, the fewer opportunities for disaster.
  • #2: The effort required to correct a casting defect is inversely proportional to its point of introduction. The more perfect your mold (and, by extension, the fewer points of failure), the less work you’ll be doing to finish the piece.

After finalizing my engineering plan for Kat’s silicone mask, I discovered a much simpler approach. Bit late, right? Fortunately, there’s now time to change: Kat’s decided that she doesn’t really NEED that mask for Halloween, and her next cosplay conference isn’t until April.


As you might have read in Part 2: Engineering the Mold, I’d planned to pour silicone into my double-walled mold, giving me a perfect reproduction inside and out. I’d created a fifth-scale maquette, a mockup of the model we’d use for Kat’s child-of-Catwoman-and-Batman mask.

Last week, this video popped up in my Youtube feed and changed everything:

As you’ll see, these folks paint the silicone into a two-part mask mold, a bit more than needed. They plunge the head armature into the face half, screw the back on tightly, and let the excess silicone seep out through the mold join. When set, they open the mold, trim off the excess, and roll the mask off the mold. Done.


That method would be MUCH easier to manage on my own, with fewer points of failure. I wouldn’t need to create the core mold with a pipe for silicone introduction, I wouldn’t have to worry about silicone setting up too fast and blocking entry, I wouldn’t need someone monitoring and plugging bleed vents as I poured, and I’d probably use less silicone, with fewer tiny air bubbles needing patching.

In addition, painting silicone into an open mold would give me more control over those big, shouldn’t-be-floppy ears. I could insert stiffening wire, use a stiffer silicone..whatever I needed without all the complicated plans to embed premade ears.

My proposed plan was breaking those Moldmaker rules: TOO complex, with too much that might go wrong early in the game, requiring a whole bunch of extra finish work at the end. I was already compromising with a commercial, head armature instead of an exact copy of Kaitlyn’s head, so my new plan needed to reduce complexity as much as possible.

New plan

  1. Build the full-sized mask model directly on the commercial head armature.
  2. Build a two-part rigid mold, joined at the side of the head, around the mask model, keyed and held together with screws, and spray with release.
  3. Remove the mask model from the armature and clean it up, then spray with release.
  4. Debubbelize and tint about twice the volume of silicone needed.
  5. Paint the silicone into both sides of the mold and insert stiffeners into the ears, making sure they’re covered with silicone.
  6. Push the head armature into the face side of the mold, press the back on and screw down tightly, refusing to freak out when the silicone pushes out the side.
  7. Let it set, remove, and repair any flaws.
  8. Paint the mask.

I have 8 lbs of silicone, enough to make at least 3 masks with this method. If it doesn’t work, I’ll have enough to revert to my original plan and try again.

Choosing modeling material

Creating the actual mask model is the FUN part but…creating it with what?

Sculpey, which forms the little maquette, is too soft and heat-sensitive for large-scale sculpting and moldmaking. Nope.

Earthen clay? My beloved Hanjiki porcelain is a dream to sculpt and my most-practiced sculpting material. It dries hard, and is easy to spray with lacquer for a smooth, beautiful surface. Unfortunately, it’s going to dry, shrink, and crack when used in such thin layers over a hard plastic surface (in many places the mask will only be a few millimeters thick), and those ears and nose won’t stand erect without internal armature. Nope.

Plastilina (or similar oil-based clays)? That’s what large-scale sculptors typically use, it’s available in the hardness I need, and I absolutely can’t stand the stuff. The odor is nauseating after awhile, it leaves an icky residue over everything that’s hard to remove, it’s sticky and nasty and ruins your clothes. And it typically contains sulfur, which prevents a full silicone cure. Nope. 

Wax? Probably my second-most experienced material. It’s extremely sculptable, I can control the hardness and thermoplastic qualities by mixing multiple waxes (all of which I have on hand), and I can always sculpt the softer wax (probably Victory Brown), then paint a layer of very hard wax, such as French Red, over the top to preserve it.

On the other hand, it’s messy, tends to wander all over the house and stain your white carpet (ask me how I know this), my wax pots are buried in a bunch of boxes, and I’d have a devil of a time removing it cleanly from the head armature (especially if I don’t want to scrape up an expensive head armature). So nope.

I did have a couple of new (to me) options:

CX5, Adam Beane Industries, is a thermoplastic molding material that is about like maple syrup when hot, hard as a rock at room temperature. It’s used for semi-permanent models in the special effects industry, and can be sanded, carved with very sharp tools, and painted. It doesn’t dent or scratch.

Downsides? It has a very short working window–it softens around 125 degreesF, becomes liquid about 135, and it stiffens rapidly as it cools, which would be a problem with those thin areas. The low viscosity makes it ideal for casting, especially slush-casting where you pour in the molten material, let it sit, and pour out the excess to leave a hollow shell, but I suspect I’ll need a lot of practice to sculpt with it.

It’s expensive, the company may have gone out of business, and I only have a few boxes of the stuff so I doubt I’ll be able to find more. But the real blocker? It’s a rigid material, shaping a rigid mold. Removing the mold from the model without damage will be difficult, especially since the design will almost certainly have locking undercuts. I COULD change plans and make a soft silicone mask mold with a supporting mothershell, but see the moldmaker’s rules about complexity…nope.

Monster Clay has the workability I need, a nice, light color that makes it easy to see detail, and can be poured, carved, and sculpted.

Monster Clay? (Monstermakers) I suddenly remembered I’d bought a big block of the stuff, recommended by a claymation sculptor friend. I dug out the box, pried a little bit out to test…and fell in love. YES!

This is also a thermoplastic, oil-based clay, but it’s made specifically for special effects artists making masks. It’s sulfur-free and doesn’t have the nauseating petroleum smell of most oil-based clays. Its color–pale chestnut–makes it extremely easy to see detail and flaws.

Best of all, at room temperature it has almost the exact texture and feel of leather-hard earthen clay, which may be the most wonderfully, nearly orgasmically workable material in the world. It will become extremely soft–like melting butter–with heat, so it works for slush-molding, but it’s stiff enough that it doesn’t need internal armatures for support.

It’s got a much longer working window when warm; it softens easily (almost too easily) with heat but quickly responds to cooling. I can use all my wax tools with it, without modification.

Monster Clay it is. Now all I need is a clay oven to soften it.

The clay oven uses a 150W incandescent light bulb, shone into a foil-lined box, to heat clay to somwhere between 125-150 degreesF.

Making a clay oven

Monster Clay is pretty workable in small amounts just by softening it in the hands, but it would take too long to cover a full-head mask that way. Clay ovens let you soften large quantities of thermoplastic material without melting them, and then hold them at that temperature as long as necessary. A clay oven is easy to make, usually with stuff you already have around the studio:

  • A lidded box big enough to contain your clay (a cardboard banker’s filebox is ideal)
  • Cheap 150W clamp light (about $9 at Home Depot)
  • Roll of heavy-duty (BBQ grill) aluminum foil
  • Silver/metallic duct tape
  • Pencil or marker of some kind
  • Sharp Xacto knife, scalpel, or box cutter
  • 150-watt incandescent light bulb (for obvious reasons, LED and fluorescent lights don’t work)


  1. The clay oven is lined with aluminum foil on all six sides of the interior, to reflect the heat from the bulb. It takes maybe 45 minutes to an hour to soften largish masses of clay to workability. (here, Monster Clay (brown) and CX5 (grey)

    Banker’s boxes usually come flat and have to be assembled, so assemble yours.

  2. Find the exact center of the lid of your box, mark it, and center the clamp light shade over that mark.
  3. Trace a circle around the light shade, onto the top of your box lid. Remove the shade, and draw a second circle inside, a quarter to half-inch smaller.
  4. Cut the smaller circle out of the lid and remove.
  5. Line the entire inside of the box, lid and all, with aluminum foil, wrapping it around the cutout in the lid, and secure with tape.
  6. Position the clamp light exactly over the box hole and tape it down. Screw in the light bulb.

To use, stick your clay in a heat-proof container, put it inside the oven, close the lid and turn on the light. It’ll take 30-60 minutes to soften the clay.

CAUTION: It’s really tempting to grab the nearest cheap 60W lamp, stick a 150W bulb in it, and use it in your oven. Don’t! The fixture will overheat and could catch fire. Use a fixture rated for 150W incandescent bulbs; if your clay is getting too soft you can always step down to a less powerful bulb.

Taking the mask model to full size

I’ve never yet made a maquette that doesn’t change a lot in in the translation to full-size; when you enlarge a smaller sculpture it tends to look bare, mechanical and a bit naive in full scale. The maquette simply brought Kat and I to agreement on the general idea of the mask; now I got serious and started filling in all the blank spaces left by enlargement.

Sure enough, the mask is evolving as I add detail. There’s still a lot of work (and Kat’s approval) to get through before I call this a final design, but this is what it looks like as I go through design iterations.

This slideshow requires JavaScript.

Next up: Finalize the model and start making the molds!