Well, here is the most current method of casting masks at Sans Souci Studios. In general it yields good results. The top pic shows the occasional mess up. This mask is too warped and wrinkled to bother finishing. The bottom pic shows a better than usual cast, nearly perfect, with just some blisters on one side of the muzzle and some missing tooth tips to repair.
So here's what I do. First I make a slip out of Paperclay. (Paperclay used to come in a prepackaged slip form, but it's been discontinued. I never got to try it.) I cut the Paperclay up into 1/2" cubes, place it in a plastic container, pour some water over it, squish it up with my fingers or mash it with a potato masher and then let it sit overnight. If the slip is still too thick the next day I add some more water and repeat the process. Sometimes it takes a few days to get the Paperclay a consistency I like.
I find it useful to have Paperclay slip of several consistencies handy. A slip the consistency of pancake batter is best for the first few layers of a cast, since it sticks to vertical surfaces and captures detail well. A slip the consistency of mashed potatoes is best for the subsequent layers of a cast, since it allows thickness to be built up more quickly. It is also useful for filling in big holes and divots in a finished cast. A slip the consistency of heavy cream, applied with a paintbrush, is good for filling in tiny airholes in a finished cast.
Paperclay slip stays fresh nearly indefinitely, as long as it's kept in a sealed container. Why? I don't think I want to know.
In case you're wondering, I use polyurethane rubber molds with plaster mother molds. I do believe slipcasting is *usually* done in plaster molds, so I thought I should mention this!
I don't use any release in the mold whatsoever when I slipcast with Paperclay, I want that stuff to stick! I've gotten some pretty lumpy, wrinkled casts out of molds that have been treated with release, as the pic above shows. It's helpful to wash the living daylights out of these molds- plain old dishsoap works well.
I apply a first layer of the pancake batter slip with a chip brush, dabbing it along the upper edges of the mask and letting it run down into the lower parts. The thinner this first layer is, the better- it really only needs to coat the rubber so that the rubber appears to change color. Any pooled excess can be carefully scooped out with a spoon. When this layer is dry I brush a coat of Sculpt and Coat over it. I resist the urge to fill in any cracks or separations in the Paperclay with more Paperclay until the Sculpt and Coat is dry, as re-wetting it can also cause it to wrinkle and deform.
I apply one or two more layers in this manner (pancake batter slip, followed by a coat of Sculpt and Coat) and then I switch to the mashed potato slip. I apply a layer about 1/8" -1/4" thick, let it dry, and then coat it with Sculpt and Coat, again resisting the urge to fill any cracks or separations with Paperclay until the Sculpt and Coat is dry. And believe me, it takes some resisting, as the cracks are large and plentiful at this stage!
Then, using more mashed potato slip, I build up additional thickness around the edges and other vulnerable parts of the mask, finally fill in the cracks and separations, and apply another coat of Sculpt and Coat. Some of the very deep cracks may require more than one application of slip and Sculpt and Coat. Once everything feels dry I remove the cast from the mold, being careful about parts such as noses and eartips that may have some hidden dampness.
This method of casting is susceptible to hidden air pockets in between layers of Paperclay, especially along the edges of raised areas such as eyebrows, noses, etc. These areas can be very weak and can cave in if the mask is dropped, etc. I check for these by pressing along suspect areas with my fingers, trying to cave them in myself, and filling in any resulting dimples with more mashed potato slip.
Then I clean and repair the cast. I clean edges and seams with an exacto knife, or a dremel if necessary. I resculpt anything that needs resculpting- lost wrinkles, lips, eartips, etc with Paperclay straight from the package. I hold the mask up to a strong light to find any thin spots, which I fill from the inside with the mashed potato slip. I fill divots with more slip and smooth them out with a wet elephant ear sponge. I let everything dry, sand down the outside of the mask (220 grit is usually sufficient, tho 100 grit can be useful for very stubborn lumps and wrinkles) and repeat the process as necessary. Once the mask is the way I want it, I apply a final coat of Sculpt or Coat, inside and outside.
I wipe off the outside of the mask with a damp paper towel to get off any dust before I put Sculpt and Coat on it, as otherwise it can ball up and make lumps in the finish. I brush it on, and then wearing rubber gloves, I smooth it down with slightly dampened fingers. Since the Sculpt and Coat dries very quickly, I apply it to smallish areas (about 2" by 2") and smooth as I go.
I have also experimented with using an initial detail coat of Sculpt and Coat, and my results are mixed. I've gotten some gorgeous casts, but when I get casts with the usual holes, divots, etc I have the extra step of cutting away the dried Sculpt and Coat from the edges in order to repair them. If you do want to try this, just apply the Sculpt and Coat thinly. If it's applied in big thick pools the top will dry but the bottom won't, since the top will have sealed the bottom away from the air.
