Copied from my thread on the subject on Den of Angels:
This tutorial example is done using a bjd. If you are doing this on a plastic or vinyl doll, you don't necessarily have to make a casting of the body part that you're working on. You can form it directly on the doll since plastic and vinyl are not as sensitive to heat as resin is. Resin can discolor or weaken if exposed to too much heat. If you do not need to create a form, you can skip steps 1-3, although you may still want to do steps 1 and 2 to make sure the thermoplastic does not stick to the doll and/or to create some padding under your armor piece so that the armor will fit over clothing.
A few months ago I discovered Worbla, a thermoplastic with some amazing crafting capabilities! Comes in sheets, you can heat it and shape it and when it cools it hardens back up again. It also adheres to itself when in it's heated state. There's already some tutorials about the basics of using the material that are worth looking at, but since we're working on a smaller scale for dolls we generally don't have to worry about foam layers or doubling up so much.
Wonderflex is similar, but not quite as easy to work with. It has a mesh backing so it doesn't stretch well and it doesn't adhere to itself as well as worbla does. But it does have it's uses.
What I'm going to write in this thread are some tips about things specific to working with worbla on dolls since dolls don't have squishy flesh that can fit into rigid shapes. But it would be good to first take a look at these pages that show some things about how the material works:
And the best place that I can find to buy it is from Cosplaysupplies.com:
If you want to try this process my way, you'll need:
paper masking tape
white elmer's glue
paints and/or spray paints
spray lacquer or varnish
small cardboard box
some packing materials
My first fairly successful attempt (2nd attempt overall) a few more pics of it further down in the thread:
Here was my first semi-successful attempt which taught me a lot about what not to do:
I learned from that first attempt that you can't use a cotton stuffed duct tape dress form because it doesn't hold the doll's shape EXACTLY. Since worbla is solid, any bumps inside it will keep it from fitting on your doll properly so you need an exact shape of your doll's body to for your pieces on. You don't want to form thermoplastic directly on your doll since it involves heat and a bit of adhesive. It's not super hot since you're handling it with your hands, but still, I hesitate to form thermoplastic directly on resin just in case.
The 2nd thing I had tried was filling the duct tape form with resin, but even though the taped form was tight, it still deformed when filled with the liquid resin
3d try took a few steps and succeeded! So here's what I did:
Wrap your doll in plastic wrap. Just a single layer because you don't want to bulk things up. You're actually sort of making a cast of the torso.
Use small pieces of paper masking tape to make as smooth a cover all over the torso as you can. You use small pieces so that there aren't wrinkles, particularly around curves and small details and crevices.
Veeery carefully cut the wrap up both sides of the torso and the tops of the shoulders so that it can be removed as a front and back piece. But DON'T remove it yet.
Measure and cut pieces of Wonderflex to form over the tape, doesn't matter if you do the front or back first, but remember to maintain the seams at the sides. Use more masking tape on the edges of the Wonderflex at the sides to make sure that your front and back templates do not stick to each other. You want to make sure that you form it as close and tight as possible.
Wonderflex is good for this step because it's just strong enough to hold it's shape while still fitting in the details.
You should now be able to remove the front and back torso templates and have something like this:
If the tape and plastic wrap came apart from the Wonderflex, that's ok, because it should still be in the same shape and be able to be pressed back into the Wonderflex "mold".
Smooth out the insides of your mold pieces a bit. If there are some pieces of plastic that are a bit too puffy or wrinkled and sticking out, you can use some light heat to shrivel and remove it. don't use too much heat because you don't want the mold to soften and deform. If needed, use more paper tape inside.
Put the 2 sides of the mold together, tape the sides up on the outsides, no need to worry about the inside. Cover the neck hole and the arm holes, leaving the bottom open. To make sure that the mold halves stay together tight, you can either use rubber bands, or wrap more tape all the way around the mold at the shoulders, waist and at the hem.
Set the mold upside down with the open bottom up in the air, inside a small box and set packing material around it to ensure that it will stay in place and not fall over.
Mix the plaster. Since plaster can be pretty crumbly, I add elmer's glue to the mix, about 1 part glue for 3 parts plaster should make it a bit more solid. Pour into the mold and wait for it to harden. The Elmer's glue will likely make the plaster take longer to harden than the directions of the plaster will say. If it's a plaster that hardens quickly, it is likely a heat curing plaster, so you want to make sure that you let it cool completely before demolding if you want to preserve your mold pieces in case you want to or might need them in the future.
Remove the extra tape and demold. Now you should have a nice facsimile of your doll's torso! Just use an exacto blade to trim the seams off the sides and the shoulders and you're ready to form some perfectly fitting pieces on it! I used some putty to round out around the nipples a bit because I didn't want the armor to have pointy nipples built into it -_-
Now for the fun stuff.
create your base pattern pieces on paper to make sure that they will fit right on your form before you cut your worbla. The worbla has some elasticity, but it's fairly thin, so you don't want to stretch it TOO much. You can press some wrinkles down too, but that's not always easy either if it's bunched up too much, so cutting proper patterns is key to making good fitting pieces.
tape your pattern to the worbla and cut the pieces.
Use your heat gun, to heat one piece at a time and form them on the plaster torso. Careful not to heat it too much and burn yourself. Worbla sticks to itself VERY easily, so you have to be careful not to let it touch itself accidentally if you don't want it to stick. You can use various tools to press any edges together. I have some sculpting tools with flat edges that I use to press things.
Now that you have your base shape, you can cut the shapes for your 2nd layer details and press them on top of that. Both surfaces have to be heated to stick properly. I like to use a hot knife and hoover it over the place where the piece is being added, and then heat the piece and press it down. You CANNOT put the details on BEFORE the initial forming because the edges where the thicker details join the thinner layer become weak points and when you try to stretch, it will stretch at those weak points and tear. If it needs to be pressed, it will wrinkle and be difficult if not impossible to smooth back out again. A hot knife is really great for smoothing out things and working on small details.
Prime the pieces to make them smooth for painting. I like Rustoleum's Painter's Touch 2x coverage primer: http://www.amazon.com/gp/product/B002BWORRW/ref=oh_details_o00_s01_i00?ie=UTF8&psc=1. You will need several layers of this. Follow the directions and add as many layers as you feel you need. You can sand between priming sprays if you like.
Unfortunately on the piece that I'm working on, I tried out a different Rustoleum primer that I thought was similar enough to the one I had been using, but apparently it's not! Because it cracked like crazy! T_T I had to try to sand it out some which is crazy difficult in such crevices. I just hope it's salvagable and the new primer will cover it well:
After this point, it really all depends on how you want to go about it. I like to use automobile spray paints because I want a finish kind of like Iron Man's armor. I think it's easiest to first spray the whole thing the color that your raised details will be. I would wait at least a day to make sure that it was completely dry and then use masking tape to cover those raised details so that you can paint or spray paint the recesses whatever color you choose. I feel that masking the raised details is easier than masking the recesses and I think that it comes off easier that way as well. But that could be subjective.
Sealing, you could use various materials, laquer, laquer spray, matte finishes, whatever is compatible with the painting materials you used. Again, wait at least a day to try to make sure the finish is hard enough for you to handle it in the next step without finger prints getting pressed into it.
Line the inside with felt. You can use various types of adhesives to stick the felt to the inside of your piece. I used hot glue on my first piece, but I was a litttle worried about any little deformations happening so I think I may try a spray adhesive with the piece I'm working on if I can get it to focus in the right area properly.
And youre done! Here's a few bad pics of my piece: