Monday, January 23, 2012

Silicone Implants

Comedy, Tragedy
Since my meeting with Secaucus was cancelled the other day due to snow, I decided to work on some small Halloween projects (after shoveling, of course).

I had read on the Hauntforum discussion boards a post about making silicone molds to cast paper clay items in. The process was lifted from Instructables, a website that contains some interesting Halloween-related projects (and a lot of dreck too).

The mold ingredients
The idea is to take regular silicone caulk -- the cheapest stuff you can find (but its gotta be silicone) -- and mix it with corn starch. The reaction between the two creates a cheap, quick mold that can conform to any surface. On Hauntforum, Jaybo used it to make an impression of a small resin skull and then used paper clay to churn out a bunch of skulls (he got the molding technique from MacabreRob who found it on Instructables with the resulting mixture called "Oogoo").

The rubber masks
On YouTube, ramathltol did a similar thing but used the plaster plate mold process. While others have used the plaster process, most notably Allen H from StiltBeastStudios, ramathltol ended up making hundreds of the paper clay skulls in what must have been a truly mind numbing process.

In his original post, MacabreRob discusses how mixing the caulk with corn starch is a little difficult because of the stickiness of the caulk, but after awhile it yields up and depending on how much corn starch you use you'll have between a few minutes and hours to work with the mixture. At a 1:1 ratio of caulk to corn starch, it you just a few minutes; at 5:1, you have 2 hours.

Pressing mask into Oogoo
I recalled, though, Allen showing how to making a silicone mold for a mask he was making, and he had mixed the caulk with naphtha -- about 50-50 he said -- which broke down the caulk and made it possible to paint on with a brush. I figured I would combine the two processes and see how that turned out.

So I squeezed out about half a regular size tube of silicone into a plastic container and eyeballed about a quarter of the amount of naphtha. I put the lid on the container and shook it vigorous back and forth and it obtained a much more liquid consistency. I mixed it with a bit of corn starch (I figure it was about one quarter the amount of caulk) and using a popsicle stick mixed it all together until smooth and flattened the surface.

The resulting mold
What I wanted to mold was a rubbery set of zombie heads I had found at the dollar store. The container was big enough for two of the small heads so I pressed two of them into the Oogoo and let it set for about 15 minutes or so (maybe a little longer, I was futzing around and wasn't really keeping track). The skulls, though, readily pulled out of the mold without any residue whatsoever.

I had intended to use paper clay, but really didn't feel like mixing up a batch, so I used plaster instead. I mixed up a batch and poured it into the mold, which had only been setting for about a half hour total. I left them in there for an hour or so and pulled one out and found the plaster was still wet. Maybe because of the silicone it stays wet longer than otherwise. While it gave the face an interesting texture, I decided to let the other head cure overnight.

The mold pops out easily
I'm not sure if it was because of having it sit in the silicone so it absorbs some of the chemical or what, but several days later now and I still find the casts slightly damp to the touch. I also notice the faces have some very small bubbles that are very brittle and easily brush away. So I'm thinking there is some absorption going on here.

Since I didn't take photos of the process, I did it tonight and noticed the plastic packaging of the rubber skulls has their reverse image molded into the plastic. So I just poured another casting of the faces, but this time using the packaging. I want to see if they cure faster than the silicone mold ones did. I'll report back my findings.

Plaster casting
Regardless, it was a fun little project that should enable me to churn out hundreds of small finials for my graveyard fence I plan to make. I think I'll make those out of paper clay (not sure how well plaster will hold up to the elements over the long haul, even sealed and painted).

The other mini project I did was used Great Stuff expanding foam to make a brain. I saw Steve from Steve's Haunted Yard (Yardhaunter5 on YouTube) do this and it seemed like a quick and easy project. And it was! Using a plastic Jell-O brain mold, I filled it about half way up and let it set over night.

Unfortunately, the results were disastrous. Although the outer portion dried to a hard shell like Great Stuff does, the inner portion -- the part that would have the brain design on it -- didn't dry, even after 24 hrs. When I pried the "brain" out of the mold. it split in two revealing a still damp interior. Now here it is two days later and the part that I left in the brain mold is still damp in parts, though mostly cured. I'll have to go back and review Steve's project to see what I did wrong.

With a Make & Take group meeting yesterday (Talking Boris Skull hack) and another scheduled for next Saturday (Coffin Creep, but we'll be working on the lid mechanism) it's great to be back in the swing of things building props!


  1. You need to spray a fine mist of water inside your mold for urethane. It needs water to cure, and the water won't travel more than about an inch through the foam.

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