Comment by Hugo on October 19, 2012 at 4:03pm

Hi all,

I'm trying to get an articulated hand but I'm having trouble with the process.
To start, I've made a hand with clay after what I did a plaster mold able to be filled by liquid latex.
The first time, I filled it with latex only and the result was quite good so I made a wire armature base on this latex hand.
I used standard wire for fingers and miliput for the palm. I placed it in the 2 part mold before pouring the latex.
After few days, I opened the mold, cut the extra latex on fingers and did this animation test.

Problems :

- Once the 2 pieces of the mold separated I used a toothpick to take off the clay stucked at the fingertips. What a mistake !
I did cuts in the plaster. What should I use to take it off without ruining the mold ?

- The armature is "moving" in the latex. Since I've bent a finger and put it back in the first position, the wire is no longer at the fingertips.
Same problem (but in the other way) with another finger which has been perforated. To fix it I put latex on it but as it happened once, I'm not sure it will be enough.
Should I put miliput on fingertips to avoid this ?

Thanks !

Comment by grecodan on October 20, 2012 at 8:34am

Did you coat the inner surface of the mold with some sort of release agent? That would help the sticking problem. Maybe try slush molding it instead of pouring all the latex at once? Before you put the wire armature in, paint a couple layers of latex into the mold, letting it dry after each coat. That will give you a buffer layer so when you put the wire in and pour the final latex the wire won't poke through the liquid and hit the plaster. When it's all cured you shouldn't have any holes.

I just recently started using silicone for latex slush molds, which I read wasn't supposed to be done. It worked fine, though. And the cured latex just pops right out.

Comment by grecodan on October 20, 2012 at 8:37am

EDIT ^^ 

I guess some release agents can destroy latex. I used to paint the inside of plaster molds with a couple layers of polyurethane, the stuff you use to finish furniture. Get the clear gloss polyurethane and coat the inside of your mold, letting it dry thoroughly between coats. I never had a sticking problem with that.

Comment by Dean B on October 20, 2012 at 11:11am

If you're using liquid latex, you're best option is to make a build-up puppet - e.g. using cushion foam for the basic shape, then layering the latex up gradually by either brushing/dabbing it on, or dipping your puppet in. Using a hair dryer or heat gun will speed up the process. You can probably make a decent practice hand from scratch in an hour or 2. Using athletic bandage/underwrap as you go will help to build quicker and adds stability to the puppet, preventing unwanted folding in the rubber.

Making a solid liquid latex puppet in a 2-part mould will produce a rather dense, heavy, hard-to-manipulate puppet. And, like you mentioned, it will take forever ("few days") to set.

Sir Hilligoss has great liquid latex build-up tutorials for a body and a head.

Comment by Dean B on October 20, 2012 at 11:27am

Can't see an edit option on video comments..?

The slipping armature wire could also be helped by using cushion foam or atheltic wrap, as it gives the smooth rubber something to adhere to. Similar to when making a silicone puppet. I think adding milliput to the fingertips would help prevent the wire piercing the rubber.

If your plaster mould is damaged easily by a toothpick, it sounds like your mould isn't strong enough. You should try increasing the powder to water ratio or consider a stronger plaster, like dental plaster, Crystacast, Crystacal R or Herculite Stone (assuming you're in Europe).

Comment by Hugo on October 20, 2012 at 4:26pm

Thanks for your help guys !

Grecodan -
The problem isn't the latex stuck in the mold but the clay of the model stuck in the fingertips of the mold. Maybe I can put some vaseline on the clay, what do you think ? I'll probably put some layers of latex in the mold rather than pouring all of it.
The milliput palm was touching the plaster mold and as you can see it on the video (the white spot), it's almost out.
Maybe, painting layers of polyurethane in the mold could be a good thing too as the plaster seems fragile.

Beyond Craft -
Thank you, that's great videos (thanks Nick !). Though I'm not sure I can get the shape I want with this technic. At least I'm more confortable with cuting clay than adding latex, but maybe I'll try it some day.
I don't know what's wrong with the plaster, maybe I did wrong with proportions... If the next mold is not stronger I'll certainly buy another one and pick in the list you gave me.

Comment by grecodan on October 20, 2012 at 8:02pm

Yes, you need to coat the clay with something before making the plaster mold. That could be as simple as water, or talcum power. Here's a good resource:

http://www.polymerclayweb.com/tools/supplies/releaseagents.aspx

I'd still paint the mold with polyurethane. It makes a nice smooth surface. Just be careful it doesn't puddle up in small bumps and wipe out fine detail. 

As I mentioned, the benefit of doing a few latex layers first, letting them dry, and then putting in the armature and doing the rest of the latex is that it will eliminate the problem of wires perforating a finger. 

Comment by Hugo on October 21, 2012 at 4:56am

Ok next time I'll coat vaseline before pouring the plaster for the second part of the mold. I think water wouldn't be enough.

Comment by grecodan on October 21, 2012 at 8:04am

If vaseline is too goopy, you might try a spritz of canola oil non-stick spray. The stuff you use for cooking. I did that a couple of times.

Comment by Hugo on October 21, 2012 at 11:26am

Wow never heard about this non-stick spray. I think we just don't use it in France

I don't even know where I can get one of these, but thanks for the tip.

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