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artist's way guided intent (june)
June 5, 2006
making my first two-part mold
by sven at 7:54 pm
Thursday (June 2) I got back into the studio and made my first two-part mold.
The mold itself is made from ultracal 30 that I bought at Stephenson Pattern Supply. Ultracal is a gypsum product that's about halfway between plaster and concrete; it's designed to capture a lot of detail.
The red clay is "cherry creek red (no grog)" that I bought at Georgies. I needed a soft clay that wouldn't damage my sculpt; an employee recommended that I select any "low fire" clay without grog. I picked a red clay so there'd be good visual contrast with my sculpt while I was working.
This sculpt has a long nose and long feet. It really ought to get a three- or four-part mold. However, I opted to go for a two-part mold.
Why? I decided that I just couldn't leap from only ever having done one-piece molds to doing a complicated four-piece mold. The material I'm going to use for casting is flexible; I'm hoping that with a little effort I'll still be able to get it out of the two-piece. ...I decided that while this is most likely a mistake, it's a mistake that I need to make in order to understand the mold-making process better. I also decided that I've been being too precious with my sculpt; there will be more sculpts -- it's OK to screw this one up.
I think occasionally it's worthwhile to go ahead with a project even when you know at the outset that it's flawed. Mistakes are an important part of how we learn.
I made a cardboard wall to hold the liquid ultracal in place... I've watched Kathi Zung's video, and she doesn't do this. She slathers the material on by hand, then shapes it with a kidney-shaped pottery tool (sort of like frosting a cake).
It may well be that I wasn't mixing my ultracal thickly enough -- or maybe I should have waited for it to get stiffer before pouring... Nonetheless, the technique I used seems to have worked out alright.
For making "keys" for the mold, I tried two different styles. On one side there's a sort of clay trapezoid with tapered edges. On the other side there are two marbles that I pressed into the clay. Initially, the marbles didn't want to separate from the ultracal 30. A gentle knock with a hammer did the trick, though. ...The two sides of the finished mold seem to fit together very well.
I extended the top of the mold using what was at hand: cardstock. It worked OK when the paper didn't have to hold back too much ultracal.
I figured out when I made my second wall that you really do need the cardboard for strength -- but if you line it with cardstock, then the resulting mold has smoother and nicer sides.
When I mixed the ultracal 30 with water, I did so in these big paper buckets that I found at Ace Hardware. They seem to be meant for house-painters... However, they very quickly became soggy. Near the end of the day, I was carrying one of these paper buckets, full with water, away from the sink -- and it started gushing water out the bottom onto the carpet!
Grrr.... No real harm done -- but on my next plaster-making run, I'll definitely be using plastic buckets instead.
When the ultracal for the first side of the mold was hard, I removed the cardboard walls. Then, I flipped the whole thing over and stripped away the red clay. I had been worried that the clay would damage my sculpt... I was very pleased to discover that it really left no damage at all.
When I was flipping everything over so I could do the other side, I had an absentminded moment where I tried to pick up the work-piece by its wooden base. Oops! While it looks like everything is firmly attached to that piece of wood, really it's just the sculpt that's held in place with tie-downs. My flub created some tiny spaces beneath the feet of the sculpt that I had to fix -- otherwise, ultracal would have flowed into the feet-holes of the mold.
There were some minor smudges of red clay left on the sculpt. It was very easy to clean these off, just using a brush and water.
After I cleaned off all the red clay residue, I used a brush to apply vaseline to the ultracal. In retrospect, I think I probably should have applied vaseline to the sculpt as well. It was a nightmare picking plasticene out of the mold later.
Doing the second pour of ultracal is pretty similar, so I'm just going to let the pictures tell the story here...
After giving the second side of the mold time to harden, I opened it up... The sculpt didn't survive at all. I had thought that plasticene -- an oil-based clay -- wouldn't stick to the ultracal. I was wrong.
Maybe I opened up the mold too soon. I know that you're supposed to let ultracal set for at least two hours -- and I only gave it one. When I opened it up, it was pretty warm inside... The plasticene had the consistency of peanut butter. Maybe if I hadn't been in such a hurry -- if I had let everything cool down -- maybe then the plasticene would have come out more easily.
Or maybe I just needed to apply a release to the sculpt itself. Vaseline would probably work. I've also heard that a clear acrylic spray can do the trick.
(Here you see those terrible buckets that I mentioned earlier.)
Even after I'd scraped all the plasticene out of the mold using my trusty loop tool, there was still an oily residue. To get this out, I needed a solvent. What I had at hand was turpenoid. Scrubbing turpenoid around with a brush, the residue came out quite easily (although scrubbing ultimately ruined the brush).
...I'm a bit worried, though. Turpenoid is a petroleum distillate. Will it leave any sort of oily residue? When you cast liquid latex in a plaster mold, it cures because the ammonia content is absorbed into the gypsum. Will a petroleum residue prevent the ultracal from absorbing the ammonia? Or will the turpenoid, since it's a solvent, evaporate from the mold -- leaving it OK for use with latex?
And here's the finished mold! I took me a bit over eight hours to make -- kinda a long time, but not over my patience threshold.
Boy is this thing massive, though! Lesson learned: Another advantage of doing a three- or four-part mold would be that you wouldn't need nearly as much ultracal.
THE SURPRISING EPILOGUE
The mold is done; I'm ready to make castings. However, just this morning I had surgery on my back to remove a lipoma (a large, non-cancerous fatty deposit). Consequently, I'm not supposed to lift anything as heavy as a gallon of milk for 4-6 weeks. How am I going to work with my monster-sized mold?
Gretchin has generously offered to help... Still, I'm having a moment of discouragement.
posted by sven | June 5, 2006 7:54 PM | comments (10) | categories: sculpture, stopmo
Comments
Yay! Sven!!! Such fantastic progress. Congratulations!! You did brilliantly! You really delve into these processes with intelligence and great gusto! It's so impressive. I think your mold looks fantastic. Don't be too hard on yourself, I'm convinced the Ultracal will not maintain a barrier due to the solvent, not in any way that would inhibit your cast in any case. Go forward confidently (when safe for your health.)
You could have Gretchin help you hoist the mold--if you changed the objective in your mind to one of "GretSven play together"--and don't get frustrated with the newness and having your mate act as your hands. The mold is reuseable, after all.
Posted by: shelley Noble at June 5, 2006 11:43 PM
Lookin' good, congrats on your first mold! Looks much more professional than any that I have done :D but you're more meticulous than me...will be watching for the casting, hope you're well soon...
Posted by: ubatuber at June 6, 2006 8:29 AM
Thank you both for the compliments and well-wishes!
I guess for a little while I'll be doing research projects, reclining on the couch... After that, maybe I'll pick up the steel armature project again?
Posted by: sven at June 6, 2006 11:32 AM
Nice work on that mold Sven. That thing really is a monster! Yeah, let it sit for a while... I have a feeling your casting won't come out anyway, and it'll really piss you off. I see you built in a chisel edge to help pry the halves apart... good thinking!
Have you heard of a "cutting edge" mold? I think I'm going to try one for my silicone puppet parts. Basically you make the edge right up against the sculpt at a sharp angle, at least 45 degrees or so, and just beyond that you create a sort of reservoir that excess casting material can drain into. It's supposed to keep sem lines to a minimum and help the parts of the mold fit tightly together even if you spill some material onto the mold as you're pouring, as in the case of my press-mold approach.
Posted by: Darkstrider at June 6, 2006 5:33 PM
Hey, that Lipoma... is that's otherwise known as a sebacious cyst? I've got one of those... just oil under the skin apparently, it's just a little lump on my back. Not to be the bearer of bad news, but I've talked to some people who also had them. They all had them removed (a painful process involving having a large open hole in your body) and in every case it came back somewhere else.
I was on a big health kick a few years back, lots of exercise and a very lowfat diet, and it all but disappeared. Came back though when I started ingesting the fats again. I decided it's not too bad, and I'd rather just live with it rather than play roulette with where it might decide to re-appear. I saw a doctor about it once, just to decide whether i wanted to remove it or not, and he got all arrogant about it... when I said something about nopt being sure if I wanted it removed or not he said "Oh, I think we'll be removing it...". I just put on my shirt and walked out. Who do these people think they are? As if they can tell us what to do about our own bodies! I think he came pretty close to having to remove my foot from his ass!
Posted by: Darkstrider at June 6, 2006 5:40 PM
Hey Mike --
I hadn't heard of a "cutting edge" mold before... Right now the main sources for mold-making info that I'm studying are the Kathi Zung DVD, Nick Hilligoss' site, and LIO's 4-part brontosaurus mold over at stopmotionworks. ...Any suggestions about good places for furthering my mold-making education?
Re the lipoma: it's different from a sebaceous cyst -- but in the early stages they can look very similar. I had my "lump" checked out some time ago, and was assured that it was not dangerous... However, it had reached the point now where it was maybe 5 inches across -- and harmless or not, I didn't want it getting anywhere near my spine.
I can sympathize about pushy, arrogant, invasive doctors. I've been fairly fortunate recently -- but nonetheless, I always put on my "I don't take no shit" attitude before walking into an office.
MY body. And I'M the only one who gets to make decisions about it. (Unless I'm unconscious -- in which case Gretchin is in charge. So sayeth the legal paperwork we went out of our way to create.)
Posted by: sven at June 6, 2006 7:48 PM
I've only seen one mysterious reference to a cutting edge mold, and that was in a nice detailed article Doug Henderson wrote at Monster Lab about an animatronic T-Rex he was making. He just briefly mentioned it... basically said the same thing I did above, but I could imagine how it would work. Pat Zung says one problem with silicone "squish molds" like I'm trying to make is if you get silicone onto the mold outside of where it's supposed to go, it's thick and can keep the mold halves from going together properly. Even in my first arm test I had a little of that.... just a slight spillage that I tried to wipe up with a paper towel, but it still made things a little difficult.
But it seems the Silicone Gods have bestowed a strange and wonderous gift upon me that might be the solution.... more in my next bloggage.
Posted by: Darkstrider at June 6, 2006 9:15 PM
another way to make a nice key way is to take a spoon and use the tip of the spoon rotate it in a circle, this carves out a very nice well. Nothing to remove.
Posted by: sandy at February 3, 2007 6:41 PM
I am so proud of you for what you did with your mold! Great work, Sven!!!
Posted by: kathi Z. at February 2, 2008 6:51 AM
Thank you so much, Kathi -- you're too kind!
There are things I'll do differently on the next mold... But the things that I did right are mostly attributable to you.
Your DVD is the single best learning aid that exists for making foam latex puppets. Over at StopMotionAnimation.com, whenever there's a newbie asking about how-to, I tell them the best thing they can do for themselves is to go purchase your DVD.
It's a tremendous resource for the stopmo community -- thank you, thank you so much, for producing it!
Posted by: sven at February 2, 2008 5:59 PM