I have gotten numerous emails recently, asking for tips with making armatures out of foil. I promised loyal Horde members, that I would write up a brief tutorial (and I use the phrase "tutorial" very loosely) on the topic, so here we go!
First, I start off with standard aluminum foil. It doesn't have to be anything fancy, you can use uncoated wire, too (operating under the assumption that you are working with a polymer based clay; folks using Apoxie, or other air-cure products, it doesn't really matter if the wire is coated or not). One common theme that I have read in those emails, is that folks like to twist the foil. I never twist the foil (wouldn't the Hanson brothers be ashamed?). Twisting it, leads to weakening it, which may not seem like a big deal, but it can be a very big deal, if your seam/joint breaks, and you have to try to go back and fix it. I simply mash the foil together in the relative shape that the piece is going to be in. Also, keep in mind how this you want your piece to be, and work your armature to be quite a bit thinner. There are few things as frustrating, as not being able to carve in details deep enough because you made your armature too thick.
I then take a little bit of the clay (I swear by KATO Polyclay), and I fortify the joints, so that I don't get any cracking in the armpits or in the crotch of the figure (should I accidentally apply too much pressure. And yeah, I totally realize all of the "crotch pressure" jokes that I just stumbled into. Anyways...).
After that, I go ahead, and apply a thin coat of the clay to the rest of the armature, to help keep it from warping while baking. I can't tell you how many times in the past, I went with just a foil armature, and had legs/arms warp while baking under the weight of the wet clay. I do a thin layer over the torso and the legs, and anything I want to add on top of that, I can be confident will stay where I put it before placing it into the oven.
Finally, while the clay is still uncured, I take an edged tool, and I score the clay. This helps any clay I add on after baking the armature, grip to the frame. Otherwise, you can find that your clay slides around on the smooth surface of the already baked clay.
Anyways, that's basically it. As you work with different products, you'll find methods that best suit the methods that YOU feel comfortable using. Definitely go with what helps you work. For me, the durability of the sculpt is very important to me, especially pieces I know I am sending off to other artists.
Always feel free to message me with questions... Making toys isn't a secret society, at least it shouldn't be in my opinion. Periodically, I'll respond to frequently asked questions with words and pictures that I think may prove helpful. Good luck with your sculpts, mighty Ironhaus Horde! I look forward to seeing the universe that you fill with your imaginations!