Howdy all! I'm new to the site, and been looking for a good community to learn from and perfect my stop-motion skills.

I'm working on my first short currently, and hit a speed bump recently with my casting. I have been following the steps on stop-motion magazine's site to cast in foam latex from my mold, and I'm using a foam latex kit from monstermakers.

Just tonight I attempted to cast my first character -- the smallest of four at 6 inches. Done at room temperature with about 50% humidity, my first batch of foam made within a minute was a solid, tough mass, and therefore couldn't be poured into the mold. Figuring to counter how quickly it set, for my second batch I spent a minute less time on the refining stage of the foam, (after the gelling agent had been added) and rushed to filling the mold. The foam latex remained liquid, and I was successful in filling my mold. After cooking it for 2 hours at 180 degrees, I took the mold out and popped it open to see how the puppet had cast.

To my dismay, the puppet looked rather collapsed -- some detail had come out nicely in the hands, but the foam itself was very weak and light. Upon poking areas of the puppet, its chest and face easily collapsed, and held their collapsed state rather than popping back to form. The in-between layer of excess foam was also INCREDIBLY frail and thin. However, the foam outside of the puppet on the mold itself had dried to a perfect consistency -- it held its form when prodded.

Due to my inexperience, I can't tell where I went wrong, and wanted to get some opinions before casting a third batch. Did I simply take the mold out of the oven too early? Or was my mistake perhaps somewhere during the mixing stages when I attempted to account for the first batch's toughness? Any advice would be extraordinarily helpful.

I've attached an image of the failed casting -- to get a sense of how the chest collapsed, that distorted ring on his belly is supposed to be a perfect circle.

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  It has been many years since I ran any foam. I'm no expert, maybe someone who does this more often will give better suggestions. I have had issues with much, much higher humidity than 50%, more like 90%! I had to run the A/C [ it was summertime ] wide open to chill the room down, and dehumidify. I was still having issues with the foam gelling too fast. It took me a week and lots of wasted material and time, not to mention ammonia-induced pneumonia and a ruined oven to finally get it right. I tried all kinds of variables, shorter mix cycles, less gelling agent, nothing worked [ for me ]. This was before the internet, and of course this website. I was lucky to have found where to buy foam latex in the back of a starlog press magazine #1 issue of " Horror Effects ". But I digress...

My solution - again, this worked for me, some may find it wrong or even appalling, to keep the foam from gelling too quickly, was to pre-measure, by weight, the amount of gelling agent specified in the recipe included with the kit [ R&D brand - no wait - it was Burman ] [ Burman's original brand before they bought GM ] [ they DID buy GM, didn't they? ] [ digress, digress... ] - - - My solution was to weigh my components with a postal scale in plastic sandwich baggies - the cheapie scales with the clip to hang the baggies onto, hang them up with clothes pins after weighing, have everything ready to go, then FREEZE SOLID just the GELLING AGENT, and pull it out of the freezer right before adding it to the mix at the right time. I ran the exact mixing schedules recommended, in the specified amounts, and the frozen gelling agent was EXACTLY what it needed to slow the reaction enough for me to be able to inject it into the molds before gelling. I never messed up another batch after that.

Like I say, some people with more experience may have better advice, or be furious with me for suggesting this method. All I can say is that it worked for me. Flawlessly. It always gelled perfectly, because it has the right amount of gelling agent. It only slows it down a LITTLE bit, just enough time to get it into the half-assed caulking gun I used for an injector, and into the mold. I was afraid to try chilling all of the components in the fridge, because I thought it might keep the foam from fluffing up right. I wouldn't dream of freezing the other ingredients. Maybe I should have refrigerated the gun first, that might have slowed it down further, but it also might have collapsed the foam, I don't know.

BUT, your problem is probably different. Did the instructions say to only bake for 2 hours at 180? The body of your puppet seems thick. It SEEMS to me that he wasn't cooked long enough. The flashing between the mold halves would be baked much more, because it's just thin.

Also, I used to bake at 200 for about 4 hours, then leave the mold in the oven to cool down. It just seemed to me, SEEMED, that is, that it would be easier on the mold, to keep it from cracking. You used an Ultracal or hydrocal mold, I presume? I have read on this site before that 180 is fine, preferable even, to 200. Good luck, and I'm curious what others have to say.



I've used Monster Makers foam for years and wonder if you've read the directions thoroughly. According to what you've reported you've made some serious errors.

> my second batch I spent a minute less time on the refining stage of the foam, (after the gelling agent had been added)

Gelling agent is added AFTER refining.  1) Whip to desired volume.  2) Refine at lower speed. 3) Mix in gel THOROUGHLY (and quickly, like 45 seconds or less for a small batch). 4) Put in mold.

> After cooking it for 2 hours at 180 degrees... the puppet looked rather collapsed

Sounds like it's undercured, meaning you didn't bake it long enough. How did you come up with 2 hours baking time?  A common rule of thumb is 3-4 hours if the mold walls are about 1" thick.

A way to never underbake or overbake is to cook at around 130F for many hours, like 8 or more.  I often throw it in the oven overnight and pull it in the morning, or start baking in the morning before I go to work and then pull it out when I come home 9-10 hours later.

> the foam outside of the puppet on the mold itself had dried to a perfect consistency

First off, foam doesn't DRY, it CURES. There's a big difference. We're not just expelling water, there's a chemical reaction happening that is accelerated using heat.

Second, the foam outside the mold cured because it was heated immediately. Any foam inside the mold won't get heat until the mold itself heats up. With UC30 and a 1" wall that can take about an hour. (Pro foam runners know these numbers exactly, I'm just ball-parking.)

Oldschooler said use postal scales. Yes, anything that gives accurate gram measures. You can get the same thing in a battery operated kitchen scale for $20.

Never heard of anyone freezing gel before, only adjusting the amount of gel. I often use about 70-80% of the recommended amount to get a little more working time. Also, if it's really humid you use less.

I usually use GM or Burman foam, and always reduced the amount of gelling agent by about a third. Recently I cast two puppets in Monstermaker foam and it worked out pretty much rhe same. I reduced the gel the first time, and it was a very slow gel, 20 minutes, so I went up to the reccomended amount on the next one and it was a more usual 6 or 7 minutes working time.
I do often reduce the mixing time for small batches. The whipping action not only froths it up and mixes air in, it evaporates some of the ammonia, and a small batch has more surface area to volume, and evaporates more. The gelling agent gets rid of the remaining ammonia so the latex can gel. (Or converts it or something. I'm not a chemist. But it is the ammonia in latex which keeps it from coagulating, or gelling.) So the full mixing time needed for a 150g batch can be too much for a 50g or 100g batch. I do a minute less at high speed, and less on the slower speeds too, but it's hard to say exactly how much. A makeup prosthetics artist who had done more foaming than me said he went by smell, he could tell by how much ammonia was in it when it was time to add the gel. I do that too now, rather than going strictly by the clock, but it does take experience. Best to keep recording everything, and modify times and gel if it doesn't work, just as you have been doing.
If you take it out of the mould and when you press it it stays squished in, it is undercured and needed more baking time. For a 10 to 12 inch tall puppet in a plaster mould I usually bake for 3 1/2 to 4 hours at 100 degrees Celsius. I forget what that is in in Fahrenheit, in Australia we haven't used it for 40 years.
If the latex collapses in the mould, leaving a perfect thin skin and a big empty space underneath, it failed to cure. The difference between curing in the bowl before you can get it i to the mould, and not curing at all, can be a fine one. At least with it curing too fast, you know right away and can mix another batch with only half an hour lost. Not curing usually means you clean up the armature and try again the next day.

> The difference between curing in the bowl before you can get it i to the mould, and not curing at all, can be a fine one. At least with it curing too fast, you know right away and can mix another batch with only half an hour lost.

Do you mean gelling, Nick? (Jackson: The purpose of the gelling component is to force the foam to retain its foamy shape until the heat has a chance to vulcanize the rubber. That's the "cured" state. Without gelling agent the foam would collapse before the heat got a chance to vulcanize.)

Duh, yes I meant gelling.

Okay, I'm definitely getting a better grasp on the entire process now. 

Huge thanks to you all for your suggestions -- as someone completely new to casting, I think I've got a much better grasp on what exactly's going on in my oven now. 

Updates to follow on a third attempt tonight!

Hope it's going OK. It's many years now since I used foam latex, and it was Sherman or GM stuff then. I can only underline the good advice given above. As with everything, you develop a 'feel' for it working well after a time. I also reduced the gelling agent a bit, but never tried the freezing method.

Is your foam filling the mould adequately? Are you injecting or filling with a spatula? Do you have some holes for excess to escape? It's worth checking all these things as well.

And you will probably not get a good result every time anyway. I reckoned on about 20% failure for prosthetic make-up pieces. Practice, practice!

This third time I made holes for excess to escape, and was filling from the bowl with a spoon before brushing through the filled mold to get rid of bubbles in fingers and problem areas.

This casting had much better results! there was but two little areas of bubble damage where a chest detail and lip's corner had a bubble each, as well as a kind of "birthmark" seam made by the foam on one side of his face, but the foam's consistency is great and holds his detail. 

Currently I'm planning to fill in those small damages with some Cabosil mixed with pros-aide before I get to painting him, but I'll post pictures later when I get a chance to get advice as to whether this is a good idea.

Thanks once more for all the support and expertise! 

Great to hear you got a usable result!

I generally settle for less than perfect casts for my own films if they aren't too bad to patch, because stripping the foam off the armature and trying again could result in a worse cast.  With puppets for other people I have to be fussier.

What sort of things do you recommend doing for patching imperfection areas? I think I'm in the same boat of settling, where damage is small enough that I don't want to risk a worse cast, but on places like the face where I want to make sure he's lookin' good for his close-ups.

For the little pit caused by a tiny bubble on the surface, I just put on a drop of liquid latex. For a bigger air pocket under the surface, there may be a good skin over it but it would look funny when the head is turned or the jaw is opened. So I might cut a piece of the foam that squished out the sides of the mould with scissors to fit the hole, and insert it though a slit. Then patch the surface with a little liquid latex.
Sometimes I didn't have any foam latex offcuts so I used soft urethane foam instead (cushion foam). Occasionally I have rebuilt quite a big section with sheet foam, as if I were making a build-up puppet, though not usually on the face. But I did remodel the face of my 2 eyed Lioclops to be a Cyclops for my skeleton swordfight clip, by snipping away at the foam latex and building up with sheet foam and liquid latex on top. It needed the original eye sockets filled in, a new central socket carved out with scissors, and the jaw widened. Eyelids were built up over the eyeball by dabbing on little lines and dots of latex, in many layers.

(Full shot of the character -- "Grebble")

(Detail of "face seam" on the left side)

(Detail of "face seam" on right + bubble on his lip)

(A small bubble on the chest detail)

Apologies for the less-than-par phone quality photos!

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