Plaster Moldmaking

This 23 inch piece by student Nancy Avergun is finished and ready for moldmaking and casting. It is based on the composition of a small Roman bronze original, and took about 18 sessions to finish.

Here it is 'shimmed'. The parting line has been determined and pieces of thin brass have been carefully inserted, separating the piece into four distinct sections. Ordinary masking tape is applied to the outer edge of the shim to extend the shim line, protect the shim from damage when the edge of the mold is scraped and shaped, and to hold the shim tightly together and prevent plaster from bleeding through and locking the sections together.

The plaster has been applied to the front of the mold in three batches. It is helpful to have a thick, strong edge built up on the seam line to add strength and rigidity to the mold. This allows the surface of the mold which covers the piece to be thinner, lighter, and easier to remove later.
Here the front of the mold is finished, and a steel tube has been lightly embedded in the surface of the front piece to add additional strength.

The front of the mold being finished, the sculpture is turned for work on the back.

The back has been covered with the initial, thin, 'splash coat'. This layer is actually thrown (or 'splashed') on the piece to eliminate air bubbles and fill every detail.

After two more thicker layers are added, the mold is now completely finished. The original clay is encased in the plaster, and the seam lines have been carefully scraped to reveal the masking tape all the way around, assuring that no pieces will be inadvertently joined together.

After the plaster is completely cured, the pieces are carefully disassembled. Here the top, back section has been removed. It was designed to be a simple shape that would come off easily. After it's removal, the other's are easier to separate.

The four sections of the mold have been removed and the clay cleaned from the inside. The original clay can sometines be removed without significant damage if the composition is very simple. But the complexity of this piece meant the original needed to be destroyed during removal.