So, I finally made the jump from small scale bit and pieces for jewelry, up to making armor pieces. I went ahead and took a fair amount of photos during the process so I could make a small tutorial. I am by no means an expert, but have received some very wonderful advice from fellow casters.
First, the Materials List:
- Plastalina clay (any non-sulfur clay can be used, including kleen clay and chavant)
- A base to sculpt on, in this case, a paper mache and foil shoulder form
- Rubbing alcohol
- Sculpting tools, whichever works for you
- Rebound 25 brush-able mold rubber
- Thi-vex thickening agent
- Smooth Cast 321
- Plaster Cloth
- Aluminum foil
- Disposable chip brushes
- Loads of mixing cups and stirring sticks
First, get your plastalina onto your form and into the very basic shape. This stuff is easily hand worked, never dries and very smooth. Once it’s into the basic shape, start forming it into a more refined shape. In this case, since I was making a very smooth sort of pauldron, my first order of business was to get it symmetrical and round.I did so by rolling the form and clay around on my cutting mat, rotating and pressing it until I had a nice, round surface. I also took this time to go ahead and trace the outer edge, ensuring symmetry. Alcohol can also be used to help smooth the surface, just apply some to your finger or the area you’re tooling to help lubricate things.
Now you can start working on details. In this case, I needed a raised edge all around the piece. Sculpting this to be round and smooth all around would have been a nightmare, so instead I rolled out some long, thin rods of plastalina and sliced them in half lengthwise with a hobby blade. These were then applied to the edge I traced earlier and gently pressed into place, taking time to smooth the joints.
Now it was time to start on her rank strips. These were cut from a rolled out sheet of plastalina and applied in the same way as the rim.
After all this working, there will inevitably be a few nick, dents and bumps in the clay, so be sure to deal with those before you’re finished. I also took the time here to press in guide holes for the EL-wire and for mounting to the costume.
Mold-making and casting:
Now, time to mold! Make sure your piece is smooth, free of flaws and the surface clean. Get all of your matierials into your working area, and have more mixing cups, stirring sticks, paint brushes and paper towels than you think you’ll need.Also, ensure you’ve given yourself enough time to finish. Brushable silicone layers need to be applied at a very specific time, and if you stop doing so and go to bed, the next layer is not gonna stick when you come back to it.Â I gave myself four hours for this particular silicone.
Before pouring, you’ll have to build a wall around the model, otherwise, the silicone will just run allover your table. I have a bag of plastalina solely for wall building, you can see the ridge I’ve built around the edge here:
Measure and mix your silicone according to the manufacturer’s instructions. Be sure to mix until there are no streaks, scrape the side often and mix gently. Don’t whisk, beat or frappe this stuff, you’ll incorporate air bubbles, which are very bad. For the first coat, don’t thicken the rubber, this coat is just to coat it thinly and get every nook and cranny of the prototype. Dab very gently with your brush, trying to not warm your sculpture or incorporate any bubbles.
(now enter the area where I have no photos)
Now, for Rebound 25, you leave this for about an hour, but start checking it at the 50 minute mark. It will be ready for the next coat when it’s tacky. Tacky means that when you touch it with a gloved hand, it’s sticky, but material does not come off onto the glove itself. The next layer can be mixed now, and I added Thi-Vex to this layer to thicken the rubber, since now I need more support. You only need a few drops.This thickened rubber should be the thickness of rich cake frosting, and can go on in a very thick layer compared to the first. Apply with strokes instead of dabs and smooth with a stirring stick if necessary. Allow this to cure for the same amount of time as the first, check for tacky, and repeat until your mold is at least 3/8th of an inch thick. Then allow the mold to cure for it’s full time, which in rebound 25′s case is 6 hours from the time of the final coat. Do -not- remove the mold from your prototype yet!
After it has cured completely, we need to make what’s called a mother mold. This is a rigid shell that will give the floppy rubber the proper support and shape when you cast in it. This is a completely rigid layer, which means on a piece like this pauldron with undercuts and such a deeply round shape, I would never be able to get the casting out if it were a one piece mold, so it must be two part. To do so, simply grab more of your plastalina and make a ridge on top of the cured silicone mold with your prototype still safely inside it. Make sure it is flush to the mold and then cover the ridge on one side with a bit of aluminum foil.
To make this mold, I chose to use a combination of plaster cloth and plaster, but any rigid, sturdy, moldable material is fine. First, I mixed up some plaster and painted a layer onto one side of the mold and up the ridge at least an inch. Once that cured, I wet my plaster cloth and added a layer of cloth atop the now cure plaster, then continued adding layers of plaster and cloth until I was satisfied with the thickness.
To make the other side, remove the plastalina ridge, but not the aluminum foil! This is the barrier between the two side of the mother mold. Now, repeat the process you used on the first side, bringing the plaster up onto the foil, also at least an inch. At the end, it should look a little like this:
Once all that dries/cures, it’s time to de-mold. First, carefully remove your mother mold, one side at a time. Next, grab one edge of the silicone and peel it off your piece. It should come off as easy as a banana peel, and you’ll notice it’s very floppy, this is why that mother mold is so important. Silicone molds do not support themselves. Clean the mold out with mild soap and water and allow to dry. You can see my three pieces here; mother mold, silicone mold and undamaged prototype sculpt.
Before casting, assemble your mother mold pieces together and hold them together either with rubber bands or clips on the ridge, place the silicone mold inside and make sure it fits snugly.
Now, for this piece, I did what’s called slush casting . This means I didn’t just fill the mold up to the brim with resin and let it set. I poured a small amount of resin (less than you think you’d need) and rotate the mold so that the resin rolls around inside and coats all of the edges. This particular casting resin has a pot life (time it remains liquidy) of about 8 minutes, so I sat there, slowly rotating and tilting the mold, making sure all areas were coated over and over, for the entire pot life. This give you a thin coat of resin inside the mold. Simply repeat this process until you have the thickness you’d like. I did there slush casts.
Here is the resin cast, next to the original sculpture in plastalina:
Now, pain, drill and distress to your liking! Here is my first practice piece. I painted it with hobby enamel and distressed it by hand. It’s not perfect (the edge rims aren’t supposed to be light green…whoops!), but everything is a leaning process in this workshop!
I hope this has been helpful to someone out there, and please do not hesitate to ask any questions you may have.