Carve or purchase a sculpture of David equal in size to the bronze statue you will create. If you carve the sculpture, use wood or foam to create David's form.
Coat one side of the sculpture with polyurethane rubber. Place plasticine clay over the polyurethane rubber mold to create an armature for the mold. Rotate the sculpture and coat another side of the sculpture with rubber and then plasticine. Continue to coat the sculpture until you have created a mold of the entire sculpture. Carefully remove the sculpture by peeling away the seams of the mold.
Coat the mold with molten wax to create a positive of the sculpture. The wax must be approximately 1/4 inch thick to accommodate the bronze pour. Clean any imperfections from the wax with a file or soldering iron.
Wrap the wax positive with tar paper and pour plaster into the tar paper tube. Allow the plaster to dry for 2-to-48 hours. Remove the tar paper. Place the wax and plaster assembly in an autoclave to melt away the wax.
Pour the bronze into the plaster mold and allow the bronze statue to cool for several hours. Remove the plaster from the bronze with a hammer and chisel or sledgehammer.
Clean and repair any imperfections in the surface with an electric grinding tool and a welder.