MAKING A NEGATIVE CAST

MAKING A NEGATIVE CAST

The first thing you want to do is lay down a drop cloth or tarp to protect the floor. (makes clean up a lot easier = )

You may add a layer of Vaseline if you wish. It will make the plaster come off of the clay easier but it is not necessary.

Next gently rub or paint on the first layer of plaster. (I'm using Ultra-Cal again, the same stone used in the Body Casting section) Be sure to get the plaster into all the crevices and be sure that there are no air pockets beneath the stone.

After you have a good thick layer built up apply 2 or 3 layers of burlap strips to the surface to reinforce the mold. (same plaster bandage process as shown in the Body Casting section)

Here I have completed one half of the cast, now even if you chose not to use Vaseline on the clay you should apply a good coating on the edge of the stone on the completed side. This will keep any excess plaster that may spill over the divider from sticking to the finished side. Now repeat the steps for the other half of the leg.

Here is the finished leg. Since the plaster I'm using has a self curing agent (self heating) I will let the cast set overnight before I try to remove it. (this will let the clay get cold and hard again and make cleaning out the mold much easier ; )

The next day I first begin to remove the barrier wall from around the top of the cast.

Next with a large flat head screwdriver (or chisel) I work my way around the divider line making sure that the two halves are not connected.

Now I gently pry the stone away from the clay. If you don't have any undercuts (interlocking areas) in the sculpture it should come off fairly easily. If you have a problem getting the stone from the clay you will definitely have a problem later getting the positive's out of the negative's. When sculpting always remember, if possible NO UNDERCUTS in your sculpture!!

Here is the cast as I pull it away from the clay and inspect it for bubbles. However if you do have any bubbles (pits) in the cast, just mix up a small batch of plaster and patch them. (similar to what was done to the inside of the Body Cast before the fiberglass was laid in)

Here is a picture of the finished negative cast for the right calf.