I did a plaster strip belly cast of my expecting wife. I am hoping for a simple solution to create a positive relief form using the plaster wrap now as the mould. I'm thinking a simple application of a coating to the desired impression surface to protect and harden it(?). Then hopefully applying a liquid/ fiber(?) layer to cast a positive finished impression knowing the plaster casting is the temporary and soon destroyed surface.I've found complex expensive solutions and hope you might offer the obvious couple of products I could use for a simple solution...
Assuming that you won't need a perfect reproduction of every small feature (which would require more expensive and elaborate methods and materials like latex or mould silicone), I recommend paper maché:
- Seal the cast so it cannot stick to the materials you apply to it.
You could opt for cling film or a big trash bag cut along the seams. You'll want to reduce wrinkles as much as possible, so be careful when laying out the plastic foil.
If you happen to have a tub of latex, brush a thin layer over the entire surface and let it dry completely.
I also contemplated covering the inside of the mold with packing tape, because glue shouldn't stick to the plasticy outside. Cut the tape into small segments to reduce wrinkling and make sure you cover every small bit of the mould.
- Form the surface of the soon-to-be cast.
I recommend ripping segments of toilet paper into 4 pieces each and applying them with a solution of 2 parts water and 1 part PVA glue (known by many names like White glue, Elmers glue or wood glue). I'v used kitchen towel before, but found that it retains it's dimpled structure too much.
For a nice surface, you'll want to lay a dry piece of paper down and then lightly push it into the mold with a brush containing some of the glue mixture. Air bubbles and wrinkles will be visible in the final product.
Lay down at least 4 layers of toilet paper, each glued securely together and completely dried, before continueing with the next step.
- Stabilize the shape.
Rip newspaper (no glossy magazines!) or thin (preferably slightly absorbant) paper into strips. These can be longer than the toilet paper peices to speed up the process. Glue down at least 3 more layers using a thicker solution of 50% water to 50% glue.
- Fill the shape.
If you were to continue this way, the final object would become extremely stable, but also quite heavy. So now it's time to fill the shape with some air.
The "traditional" way is to loosely ball up entire sheets of newspaper and glueing them on with the same strips and glue as used before. You could also incorporate modern materials like packaging peanuts, bubble wrap or pieces of styrofoam. Use whatever you can scavange from the trash.
It's important that these fillings are not much larger than a human fist. You'll want to glue each bit of filling down by completely covering it in paper strips and glue mixture.
Fill the mold up to aprox. 3 cm / 1 inch below the final capacity that way.
- The final stabilizer.
The center of your cast should be nice and sturdy by now, but the edges can easily pull and twist out of shape. To add a scaffolding to the edge, spread some of the glue mixture onto a big sheet of newspaper or packing paper. Then roll it up into a messy tube and twist the tube into a spiral. Press this spiral onto the edge of the cast and glue it in place with more paper strips. If you want to be extra sure, you can repeat the process and add a second ring or you could add struds that cross from one side to the other.
- Finish your cast.
Well, get it out of the mold somehow... not much to say here.
If you don't like how the surface turned out, you can add a final layer of toilet paper on top to smooth out some irregularities. Smaller pieces of paper create a smoother surface.
After it's completely dry, you can paint it with any type of paint that isn't too watery, like acryllics or wall paints.
I once made a shark head for a halloween costume that way. It was formed over a baloon and became rigid like a helmet (it also sounded like one when knocked).