Hey stopmotimators, last June I made a dozen or so puppets. They turned out great. Now, a month and a half later, I'm having repeated collapsing issues using the same setup.


This is my setup:

  • Originals made out of Van Aken plastalina (sulfur free) and wood.
  • Plaster molds (densite plaster from dickblick.com)
  • Vaseline used in plaster casting process as release agent
  • Painted a latex skin inside the two part mold
  • Used a wire armature held together with plumbers epoxy for the puppets
  • Poured in Smooth On FlexFoam-It III

The only variable is the time - it is hotter and more humid now in August, though since I've started casting again this month I've experimented switching from AC to none AC, from a room with a dehumidifier to a none climate controlled room and had the same issue no matter what.


Today, I demolded my creations after only letting them sit in the mold for 45 mins or so (I've left them in for as long as over night before). They looked pretty good right off the bat, but they had a little bit of collapsing around the legs. I returned later to find that they had collapsed further since demolding... they all look like wrinkly old men and not plump little puppets! So this time, at least, the collapse happened not right away but over a period of time.


Also of note - the Smooth On foam that's left in my plastic mix cup does foam up and does not collapse. So it seems the issue is with my mold or setup. 

I called Smooth On, they were stumped. Any suggestions?? Very infuriating, especially considering my success in June.

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Dear Nick,

Thanks for your reply. I love your work. I have seen you use liquid latex ( which solidifies into the rubber) for a lot of your characters. Is there a way to use that latex in the plaster molding and latex casting technique? I have tried, but because the mold is air tight, the latex inside would not dry. Though I did not have a channel in the joined two part mold to pour in the latex but simply poured it in the one half, allowed it to cure a bit so it does not spill, and then put it on the other half of freshly poured latex. This for the entire body of a character( minus the head) which has a slightly detailed muscular structure. Can one achieve the desired result in latex casting, or should I use silicone for a better, long lasting result. I am new to the world of silicone, foam latex, having just used clay and natural latex before. 

There is another material which I read about was Soma-Foama from Smoth-on. It is a silicone based foam but has an extremely fast pot life of 30 seconds. Have you used it? 

Regards,

Pushan


StopmoNick said:

I believe the 2 part urethane foams have a shelf life, like most materials. I think that is what the smooth- on stuff is? But generally i find mine becomes unusable because the brown stuff has crystalised. If the 2 parts are still liquid it generally works. Don't know.
I didn't notice, when I posted a few hours ago, that this is an old thread.

Liquid latex can be cast in a plaster mould, but not to make a solid object. You use it to make a skin.
First, you don't use any release agent on the mould, you want the plaster to absorb the water from the latex.
You pour latex into the mould, and let it stand for a while. Could be 20 minutes, could be an hour. Then your pour it out of the mould, back into your latex container. The latex touching the plaster thickens up as the moisture is absorbed, so some of it is left behind, coating the plaster. The longer you leave it, the thicker that layer gets.
One you have poured out the excess latex, you leave it to dry. This might take overnight, or longer. Moisture will continue to evaporate from the plaster, and from the inside of the latex cast a little, until the latex is dry. The inside is very tacky and will easily stick to itself, so you need to squirt some talcum powder into it and shake it around. Then open the mould if it is a 2 piece closed mould. Peel the latex off the mould, and you have a hollow rubber cast, like a mask or rubber glove. If you want it solid, you can fill it with urethane foam before you open the mould, like I think the original poster was going to do.
Richard Swenson makes buildup puppets, but cast sections of latex skin to glue over the cushion foam. He has some tutorials at his Bluworm channel at youtube. He uses open, one piece plaster moulds for that. It gives him the sculpted detail where he needs it most.
I tend more to either build up by painting latex over the foam, without a mould. If I want part or all of it to be sculpted and cast, I do that part in foam latex or silicone. So my Cthulhu body is built up, but the head is foam latex. Foam latex is cast differently, it fills the mould and is baked, so it's a solid object, not a thin skin. But I do have a little tutorial at my StopmoNick channel at Youtube on making hollow liquid latex shoes by the method I was describing. Sorry, using iPad and can't figure out how to paste links in ios.

I have not been able to buy Soma Foama in Australia where I live, and suppliers in the US will not ship it, so I have not tried it. I don't actually like silicone much, I am much better with foam latex for most things. It is ok for heads, but a bit heavy for the whole puppet. And it is hard to paint, if I thin the silicone and pigment down enough, it sometimes fails to cure and has to be washed off. Soma foama would help with the weight problem if I could get it.

Dear Nick,

Thanks a lot for your prompt and valuable advice. I have already seen your latex shoe video and also have been following Richard Swenson's work on his channel. I guess the partial, open mould cast is the way out if I want to use latex. Will try it and see. It's just that on a project with a tight deadline the build up process is a bit slow. And since the weather condition, quality of latex also matter, the model making time is quite a bit. Whereas with silicone, I think it's faster. But I will try it and see. I tried the build up process with latex first. But found it difficult to control the volume of latex as per the character's muscular structure. The outcome was not good. instead of well finished muscles, the character's body was bumpy all over. I think a careful and slow approach to the open mould process will work better.

Regards,

Pushan 

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