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casting in urethane foam
April 11, 2007
foam latex - first attempt
by sven at 10:25 pm
Monday (4/09) I did my first run of foam latex. It was a complete failure. Not unexpected, but demoralizing nonetheless.
Yesterday I did my second foam run. The results (pictured above) are unusable -- but still an improvement.
Here's the original sculpt, which I did back in May 2006. Sort of a wingless bird creature.
And here's the mold that I'm working with, which I made last June. It's just been sitting around, waiting for me to get back to my line of research on casting materials.
Why am I getting back to this project now? Because I wasn't happy with the tentacles on my first elder thing puppet. I want to test some different materials -- and rather than go through the whole process of making a new mold, I figured I'd get through my first mistakes more quickly by just using the mold I already have.
For the same reason, I decided not to bother with making an armature right now. This is purely about figuring out how to get the foam latex to do what I want it to.
I bought a new mixing bowl and whisk attachment for my kitchen mixer that will be dedicated to foam latex. I covered the mixer's head with a plastic bag to help protect it from splashes. A plastic bag underneath the bowl would be a smart addition, too, next time.
I looked around several stores for a a cheap, digital combo-thermometer/hygrometer (humidity detector). I finally found this one at Walmart, which just what I was looking for. It cost about $8. (Radio Shack was a real disappointment -- they only carried a $40 model.)
First thing to do: dust the inside of the mold with mold release. I need to remember to pick up a big batch of cheap acid brushes at Harbor Freight... You go through a lot of them in most casting processes.
After the mold release dried, I took it out on the front porch and dusted out the extra with a chip brush. You know it's dry when it's turned from clear to white.
FIRST RUN
For my first foam run I decided to do a standard batch -- 150 grams of latex base -- so I could get a feel for how much that makes. The room temperature was 69 degrees, and humidity was 40% (it rained earlier in the day). I decided to go with the "normal room schedule" (68-72 degrees F).
The bad smell of foam latex is legendary. I wasn't all that impressed, though.
When you open up the canister, you get a strong smell of ammonia. If you've worked with liquid latex before, it's about the same.
When you bake the foam you get more of a sulphur smell, like eggs. It lingers in the room... But after airing out the studio and lighting up some vanilla candles, I think we'll be OK.
When I poured the first three ingredients into the mixing bowl, their level was about an inch below the bottom of the bowl's handle. When the foam reached peak volume, it had risen about halfway up the bowl's handle.
The foam gelled before I could get it into the mold. This was probably within a minute of turning off the mixer. I was trying to quickly brush some foam in with an acid brush, and then...
As I tried to see if I could quickly get at least some of the foam into the mold, it collapsed into a gummy wad, about the consistency of bread dough.
I noticed that the room temperature shot up to 72 degrees just during the last minute or two of the run (the thermostat turned on). That was probably a contributing factor.
SECOND RUN
Before I could do the second run, I had to clean out the mixing bowl, the whisk attachment, and the mold. I reapplied mold release.
The temperature was 68 degrees; humidity was 40%. I decided to decrease the refining period from 3 to 2 minutes, and the ultra-refining period from 3 to 2 minutes. I decreased the amount of gelling agent from 14 to 11 grams.
This go around I had enough working time. I quickly brushed foam onto the mold walls, then poured more in until each side was full. The foam had the consistency of whipped egg whites.
I strapped the mold shut... My straps are 13 feet long -- which is way too long. I used twist ties to try to keep the spare length out of the way.
The flightless bird is fairly bulky puppet; even so, I only used up between half and 2/3 of the material that I made. I estimate that there are between five and six 150 gram batches in my kit... So I've already used up a fair amount.
There was an area of foam at the very bottom of the bowl that never gelled. This suggests to me that there's an area there that the whisk doesn't reach... Good to know!
I baked the mold for four hours. I was aiming for 190 degrees. My oven thermometer revealed that it was difficult to get this temperature. The oven tended to hover at 180 degrees... And then if I turned it up to 200, it would sometimes go up to 210.
The initial demolding looked promising. The rear of the bird had a big air bubble -- but was otherwise pleasantly springy to the touch.
The nose, however, was another matter. Not only did it have a huge air bubble in it -- when I demolded it, it collapsed like a bad soufflé.
I should have let this mold bake for at least 6 hours... And maybe more. Not only is this a rather puffy character -- the mold is also ridiculously huge. I think the stone must have been doing a lot to insulate the nose from the oven's heat.
The entire thing has shrunk a little bit... But the rear end has maintained a consistency that I believe is what cured foam latex should feel like. So: progress.
This morning I washed the foam in soapy water, as you're supposed to do. It was pretty neat to watch the foam suck up water.
After squeezing out the water, there are wrinkles in the foam that I don't think are going to come out. I know that it's the nature of foam to wrinkle... Still, this doesn't make me love the material more!
I'm slowly getting the feel for this stuff... But I'd rather be using a material that involves less guesswork and witchcraft in its preparation.
I'm reminded of the silicone vs. foam latex comparison I did last May. Back then I concluded that I'd probably wind up using silicone as my primary casting medium. Now that I've had a little experience foam, silicone is seeming pretty appealing once again.
posted by sven | April 11, 2007 10:25 PM | comments (13) | categories: stopmo
Comments
i understand your frustration! feeling like my materials included an unsettling proportion of "guesswork and witchcraft" is one of the reasons i decided to put calligraphy on hold for a while. not that i think you're giving up, but i understand the troubles. :)
Posted by: gl. at April 11, 2007 10:37 PM
Aww man!! I feel your pain~~~~ it took me and shel a good 3 batches to get a decent casting.
smart move lowering the curing agent.... we have all our own measurements which are totally different than the directions on the instructions.
also cut time out of your mixing time.....this gave us a lot more time to work.
Shel and I both can do the foaming....but she really has the CRAFT down....she creates perfect puppets in one go
...while it still takes me a couple to get it right...Ha!
Dont give up though....foam is incredibly good once you get it right.
jriggityPosted by: justin rasch at April 11, 2007 11:11 PM
@gl: Yeah -- as I was wrestling with the foam, I totally had your struggles with the calligraphy materials echoing in my head. There was even (at some quiet, only semi-conscious level) a tiny bit of pleasure at getting to "share your pain." Weird, I know. :-P
Posted by: sven at April 12, 2007 12:05 AM
@Justin: Hey -- I really appreciate the encouragement!
You and Ubatuber get most of the blame for tipping me over the edge, making me finally think that I could do foam latex...
Foam latex is the stuff of the gods in my imagination... It's that magical manna from stopmo heaven that only Harryhausen and Tippett have the power to conjure. Me try foam? Unthinkable!
Thanks for the tip about the mixing time -- I'll have to try that. I've still got 3/5 of a kit left, so it'll happen... Although, with the pressure to be making progress on Let Sleeping Gods Lie right now, it's unclear when the next round of foam experimentation is going to be.
Right now I'm hankering to try painting a batch of DragonSkin silicone into the mold. I know that sulphur (from latex) can inhibit a silicone cure -- but it would be extremely cool if I can try out three different materials in one mold. [There's a post going up about urethane foam tomorrow!]
Incidentally, one really cool tip about silicone that Strider passed on: If you bake it at 150 degrees, you can cut the cure time down from 6 hours to 30 minutes! That, plus the ease of getting the chemicals to work, plus Henry Selick's conversion from foam to DragonSkin -- has me thinking it really deserves a good try.
Posted by: sven at April 12, 2007 12:18 AM
Ah Sven.... tireless experimenter extraordinnaire!
I wonder if the shape of the mold caused part of the problem? That front area where the casting just needs to compress and slide out might destroy the foam cell structure if it wasn't fully cured? Not sure.
But I think you're right about the thickness of the mold also being a contributing factor. In fact, I'd recommend making a new mold, one that separates where it needs to so you don't have any parts submerged down in solid Ultracal, and where the outer shell isn't more than an inch thick anywhere. Of course, watch Kathi's video before starting in!
You might also want to try a half-batch or even a quarter-batch next time.
Posted by: Darkstrider at April 12, 2007 2:42 AM
Oh, and also you want to lift the bowl and make sure the whisk is making contact all the way to the bottom. I don't know if your machine allows it, but if possible you can also turn the bowl backwards from time to time by hand, or maybe use a spatula to push foam from against the sides/bottom into the whisk.
Posted by: Darkstrider at April 12, 2007 4:02 AM
You definitely need mystery pods to extend the work time of the latex. That gunk'l'dunk always hardens too fast.
Posted by: Shield at April 12, 2007 6:24 AM
Hey man, you're progress lately has been fantastic....I was so excited when I saw the title of your post, but I'm sorry it didnt work out and that you are discouraged :( Keep trying!
My first instinct was that you cut down the gelling agent too much the second time? from 14 to 11 right? (sorry if i'm reading that wrong) I would suggest trying smaller increments, 14 to 13, to 12......not enough gelling agent could be why the cure didnt happen right and why there was still some ungelled foam in the bowls bottom....
but then, Im mostly a newbie so who knows? I definitely think Shel is the expert here :)
Posted by: ubatuber at April 13, 2007 8:07 AM
@Mike: Good advice to rewatch Kathi's video... Actually, I did re-watch it on the day I started foaming -- which prompted a quick shopping trip to pick up straps (for lashing the mold halves together) and a digital humidity detector.
I really do think that the mold thickness was the biggest problem on this run... I needed to bake for a lot longer in order to get the heat into the center of the mold.
If I really needed this puppet right now, then I'd consider doing a 3-part mold. The back side is OK -- but that nose ought to be dealt with as two separate pieces.
But, oy... Learning three-piece mold-making will just have to wait for another day!
Posted by: sven at April 18, 2007 1:09 PM
@Shield: Ah! That was exactly the problem!
Hoka hoka hey!
Posted by: sven at April 18, 2007 1:11 PM
@Ubatuber: Thanks for the encouragement!
I'm really torn about foam latex... I have moments where I can totally imagine the tentacles on the Elder Things being made out of this stuff... But then again, the studio still smells kinda funny -- which isn't so good when you have a shared space.
I'm going to have to do some trials with the DragonSkin for comparison... The problem of what material I should be using is just going to keep nagging at the back of my mind until I've exhausted every possibility.
I'm really looking forward to the day when I've figured out my personal casting strategy, and can just forge ahead with puppet fab whenever a character occurs to me. :-)
Posted by: sven at April 18, 2007 1:18 PM
Recently used latex to create a monkey mask for a theater production. I must have got lucky for the first time worked like a charm with the exception of a small air bubble. We had been using that mask for a while and when I set off to remake the mask yesterday I never thought I'd run into so many issues. I'm on my third batch and have come to the conclusion that I'm not baking long enough.. but was hoping for some feedback on some things I ran into.. when mixing a 150g batch of gmfoam it mentioned to whip for 10 minutes, but I noticed that it frothed up pretty quickly and by sticking to the 10 minutes the mixture shrank. Sort of like making whipped cream - you gotta stop or you will unwhip the whip. So this time I did not stick to the times. I lowered the speed on my kitchenaid and made sure the consistency looked even. Then I began adding the gelling agent. I just put it into the oven, so I should know the results in about 6 hours.
Joe
Posted by: Joe Rosato at June 14, 2007 10:12 AM
Hi Joe! Thanks for sharing your experience with the foam!
Posted by: sven at June 14, 2007 11:59 PM