Tuesday, June 06, 2006
The Skin is in!
My Dragonskin and related products have been coming in from various sources for a few days now, and I've been doing some testing. My main supplier has been www.smooth-on.com, but a few assorted odds and ends have come from www.burmanfoam.com (including the incredible resource Silicone Art, a book giving exhaustive detail on casting, molding, tinting, painting, and finishing silicone, as well as a few other tricks). My first test was very simple... I just wanted to test compatibility of the platinum-cure (extremely touchy) Dragonskin silicone with Chavant NSP (a wax-based, non-sulpherated plasticene, designed for use with platinum-cure silicones) and my preferred super-sculpy/premo blend. So I made up two little thimble-sized cups, one from each material, and mixed up a small batch of Dragonskin that I divided into them. I also wanted to test the difference between Silicone Oil and Slacker as a softener, so I added about 50% Slacker into the NSP cup and a similar (actually a bit larger I believe) amount of Silicone Oil into the Sculpy cup. Patrick Zung told me that he's been mixing up his silicone additives lately with "ever increasing reckless abandon", which sounds good to me, as I'm really not a meticulous person and I tend to work rather sloppily. In fact I was a bit worried that my lax working methods (and not exactly clean room environment) might inhibit the cure of the Dragonskin, but I wanted to find out, so I set to work with some reckless abandon of my own. Let me put it this way... if a platinum cure silicone requires me to transform from Oscar Madison to Felix Unger, then it's not for me. The results.... both batches set up perfectly overnight (Dragonskin takes like 8 hours to set up at room temperature). And I do mean reckless abandon... I only used one cup and just poured out approximately equal amounts of parts A and B, and I just totally estimated on the amount of pigment and plasticizer to add. Both samples came out really nice and soft, in fact once you pick them up it's hard to put them down... you want to just idly squeeze and knead them and stretch them out again and again.
So here's my second test. I wanted to sculpt and mold a simple arm shape with a wire armature inside, to check a number of things:
1) will three strands of 1/16" armature wire be strong enough against the resistance of the silicone? (yes, no problem at all)
2) I wanted to test using a stone mold (Ultracal-30) and waterbased clay dividing wall and make sure neither material adversely affects the cure of the silicone, and to just make sure I was using the right mold release etc. (again, no problems. My mold release was 1 part dishwashing detergent in 2 parts isopropyl alcohol. Happily, no matter how vigorously you mix, it won't foam up!)
3) To see how the silicone acts when animated... will it wrinkle and fold bizarrely, or flex smoothly? (see below for the answer)
4) I also wanted to try the simplest casting method I know of, just filling both halves of the mold with silicone, laying the armature on top of one half, and then slapping them together. Pat Zung voiced reservations about this method and has developed a complicated injection technique that scares me to think about. Happily, my initial test of this simple technique worked like a charm, with one problem that can be easily addressed. See below.
Simple 2-part Ultracal-30 mold.
The arm casting is hard to see clearly because I didn't use quite enough white pigment and it came out translucent. I want my puppet parts to be opaque white, over which I'll paint in a technique that I hope will end up looking like the Scott Radke heads.
You can see the silicone bends very nicely with little or no wrinkling. Very fleshlike in fact. I'm loving this stuff! There are a couple of holes where the armature was touching the mold, in fact there's one right at the elbow joint and a couple at the wrist, and these cause some odd wrinkling and puckering. But I think when I try a two-step process that involves painting a "skin" of silicone into each mold half and onto the armature and letting this set up before filling with more silicone and clamping it together I should be able to conquor this problem. There's also a large air pocket on the underside of the forearm... another problem that should be solved by the skinning technique.
One of the important things I learned from ToxicPapa is that you can speed up the cure time of Dragonskin dramatically by putting it in a 150 degree oven. It will cure in half an hour rather than overnight. I really like this, better than the idea of using an ultra-fast catalyst, which would have the negative effect of giving me less time to work with it before it starts to set up. This way I get the full 20 minutes for mixing in all the various ingredients and carefully painting it in or filling the mold, then I can demold in 30 minutes. I tried the oven cure thing, and it works like a charm.
Next I intend to try another casting, but using the skinning method I described. I also want to try sanding the seam lines with wet/dry sandpaper and icewater as ToxicPapa recommends (Tom McLaughlin recommends sandpaper and alcohol I think). I'll also try ouit painting techniques and some patching for those inevitable mishaps where you trim the seam lines a little too closely.