Hey everyone! Newbie here on the site but well knowledgeable in animation.

So I am working on stop motion project that I am certain I want to cast my figure in Silicone (what kind I still have to research). I originally had thought of Silicone Mold with a Silicone Figure and through some research found out that it can stick to it self so make sure it's properly covered so casting can separate from the mold.

Then with more extensive research, I been hearing stop motion studios using polyurethane molds. Durable, long lasting, rigid, something that is catching my interest in using. However a lot of polyurethane is usually clear when applied, so now I'm a bit confused (maybe a different kind of polyurethane?). Noticed Smooth-On sells Urethane Resin, so I started looking into that. Just by look, it's kind of close but I'm still confused, don't want to blow money and end up wrong. So now I'm thinking "was something else added to the mix like a powder?".

Best example of the mold is from ParaNorman and found that Adam Savage has visited Aardman Animation Studios where what looks like they use the same material for the mold. The guy that Adam talks to even states it's a polyurethane mold. Both images are included below.

Again, I would like to go in that direction for a mold because I might have to make more than one cast in the future. So any advice for what material I should do or look into for a silicone figure would be helpful. Thanks.

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I have cast silicone puppets in moulds made from plaster (Ultracal), from fibreglass with polyester resin, and fibreglass with epoxy resin.  All of them work fine.  The fibreglass moulds are able to be thinner and lighter, but still strong - shells rather than blocks. Was good when a client wanted me to post the mould to him overseas.  Polyester resin is cheaper, but stinky while mixing it and applying it, and may take a few days for the smell to go away.  It can be used with either chopped strand fibreglass matt, or with the woven fibreglass fabric. Epoxy resin is more expensive but does not stink, and it only works well with the woven fabric.  It does not seem to be able to soften the binder that holds the chopped strand mating together, as polyester resin and wet plaster both do.

I haven't used any rigid polyurethane materials.  I am about to use some flexible polyurethane to make a mould for the first time, because apparently this particular mix can be painted onto the vertical surface of my plasticine sculpt, where silicone would just flow down and pool on the bottom.  It is too large to make a box and pour big thick pieces, so I want to make a thin flexible mould and back it up with a fibreglass case mould (aka Mother Mould) to keep it in shape.

The platinum cure silicones mostly used for puppet casting  (Like Platsil or Dragonskin or Ecoflex) are sensitive to many materials, so I would test to make sure the polyurethane does not inhibit the cure.  But I doubt that it would be a problem.  Especially if studios are using it. Mostly it is the sulphur present in some plasticine, or in latex that has previously been cast in a plaster mould, that stop it curing.  

I usually add some Q-cell glass micro-balloon filler to the first coat of a fibreglass resin mould, which thickens it a bit and makes it look white.  That is instead of using a gel-coat - saves buying a second container of resin.  For solid casts I add some as well, as much as I can get away with without making the resin too thick to pour into the detailed bits of the mould.  It is very light weight, being made of tiny hollow spheres.  Unfortunately I have no experience doing this with hard urethane. (Or doing anything with urethane, other than the 2-part urethane foam.)  I don't know if the urethane would be used with fibreglass reinforcing or not - those moulds in the photos you posted just look like big solid blocks, so probably not.  So sorry, not quite the specific help with polyurethane you were looking for.

The urethane mold material that studios like Laika and Aardman are using is (or at least virtually identical to) BJB Enterprises' TC-816 and TC-1630. They're a mineral filled urethane, usually borosilicate glass, which makes it a lot stronger than just plain polyurethane resins. Smooth-On also makes a somewhat similar mineral filled urethane resin called Smooth-Cast 385, which is very different from their other casting resins. Standard casting resins that aren't filled are pretty brittle and would crack fairly quickly if used as a mold material, the mineral filled urethanes have loads more compressive and flexural strength.

The BJB urethane resins are really great mold making material. Pretty nasty stuff to work with though, in my opinion worse than working with epoxy resins. It's very irritating to the skin, eyes, and lungs, so you'll want all of the proper PPE (cartridge respirator that filters organic vapor) and have a dedicated workshop space with lots of ventilation. I will say that for as nice of a mold material as it is, it is quite expensive. Loads more than Ultracal-30 and a fair bit more than epoxy resin and fiberglass molds. Polyurethane resins have to be poured as a block mold (like plaster molds), so you will go through a fair amount of material. Like Nick said, fiberglass resin molds can be run a lot thinner, which means a lot less material and cost compared to urethane resin molds. I really like using epoxy fiberglass molds and would probably recommend that route over rigid urethane molds, especially if cost is an issue. I really like Smooth-On EpopxAmite 101 and 6 or 8 ounce fiberglass fabric.

If you're in the states check out Brick in the Yard Mold Supply, they carry BJB and Polytek primarily, and have really great use case information and videos for all of the products. I've used their Platsil-Gel silicones a ton for animation and recently tried the TC-1630 from them for some molds. Polytek Platsil-Gel silicone WILL cure against TC-1630, but a lot of other platinum cure silicones (like some of Smooth-On's for example) won't cure well (or at all) when used with it. In general platinum silicone compatibility with urethane molds varies a bit from manufacturer to manufacturer so be sure to read up on particular products if there is any doubt.

Great info, Ethan!

But let's hear it for good old Ultracal, or Crystacal R. You can certainly take multiple casts from a decent plaster mould. It is cheap, fairly low hazard, dust being the major irritant. And it is relatively easy to get good results. I wouldn't go for anything else, unless I absolutely had to.

Thanks for this great info! I was in contact with a guy in Chicago that sells and specialize these kind of materials to toss around some ideas. I originally was going for Smooth-On Urethane Resin 300, the guy suggested 310 for longer work time since it'll be my first time making a resin mold so it kind of make sense. 

I'll be sure to check these stuff out! Thanks again!

Ethan Bartholomae said:

The urethane mold material that studios like Laika and Aardman are using is (or at least virtually identical to) BJB Enterprises' TC-816 and TC-1630. They're a mineral filled urethane, usually borosilicate glass, which makes it a lot stronger than just plain polyurethane resins. Smooth-On also makes a somewhat similar mineral filled urethane resin called Smooth-Cast 385, which is very different from their other casting resins. Standard casting resins that aren't filled are pretty brittle and would crack fairly quickly if used as a mold material, the mineral filled urethanes have loads more compressive and flexural strength.

The BJB urethane resins are really great mold making material. Pretty nasty stuff to work with though, in my opinion worse than working with epoxy resins. It's very irritating to the skin, eyes, and lungs, so you'll want all of the proper PPE (cartridge respirator that filters organic vapor) and have a dedicated workshop space with lots of ventilation. I will say that for as nice of a mold material as it is, it is quite expensive. Loads more than Ultracal-30 and a fair bit more than epoxy resin and fiberglass molds. Polyurethane resins have to be poured as a block mold (like plaster molds), so you will go through a fair amount of material. Like Nick said, fiberglass resin molds can be run a lot thinner, which means a lot less material and cost compared to urethane resin molds. I really like using epoxy fiberglass molds and would probably recommend that route over rigid urethane molds, especially if cost is an issue. I really like Smooth-On EpopxAmite 101 and 6 or 8 ounce fiberglass fabric.

If you're in the states check out Brick in the Yard Mold Supply, they carry BJB and Polytek primarily, and have really great use case information and videos for all of the products. I've used their Platsil-Gel silicones a ton for animation and recently tried the TC-1630 from them for some molds. Polytek Platsil-Gel silicone WILL cure against TC-1630, but a lot of other platinum cure silicones (like some of Smooth-On's for example) won't cure well (or at all) when used with it. In general platinum silicone compatibility with urethane molds varies a bit from manufacturer to manufacturer so be sure to read up on particular products if there is any doubt.

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