Using the acrylic pieces and glue gun, build a topless box for the sculpture to fit in. The box should be at least 1/2-inch bigger than the sculpture on all sides.
Fill the bottom half of the acrylic box with molding clay, pressing the clay solid, to avoid crevices.
Lay the sculpture on its back inside the acrylic box, on top of the clay with the base of the sculpture flush to one side of the box. Press the bottom half of the sculpture into the clay. Using the pencil, press the eraser end into the clay in four to six areas surrounding the sculpture to create a key.
Spray the inside of the box and sculpture with mold release. Pour urethane into the acrylic box, filling the top half of the sculpture and box. Let dry 24 hours.
Using the metal spatula, remove the acrylic side frame from the bottom plate. Remove the clay from the bottom half of the mold.
Spray the mold release to the bottom side of the acrylic box and sculpture. Pour the urethane into the acrylic box, covering the second half of the sculpture. Let dry 24 hours.
Remove the urethane mold from the acrylic box. Remove the sculpture from the urethane mold.
Place the mold back together. Place an acrylic piece sandwiching the left and right rides of the mold.
Use the rubber bands to band the mold and acrylic pieces together.
Pour the casting material into the bottom of the mold. Let dry 24 hours.
Remove the rubber bands and acrylic pieces from the mold. Open the mold, and pop out the new sculpture.