6: Pouring the Bronze
OVERVIEW | MODELING | MOLD MAKING | WAX CASTING | WAX CHASING | CERAMIC SHELL | POURING BRONZE | CHASING | PATINA
|Now that the ceramic shells have all the wax burned out of them they
are placed into the pre-heat oven. This is done to evacuate any moisture from the
ceramic shells, thus avoiding the creation of any steam during the pour. The bronze
melts at 1850¡ Fahrenheit but often is not poured until it is superheated to
2150¡. The pouring temperature depends on current ambient conditions and the design
of the sculpture being poured.
Bronze ingots are put into a bonded silicon carbide crucible and then melted and brought up to a pouring temperature in a specially designed furnace. When the bronze is ready to pour, the ceramic shells are placed upside down with the pour cups facing up and packed in sand to stabilize and insulate them. The crucible is then lifted out of the furnace by a mechanical device and hoisted over each ceramic shell as the bronze is poured from it.
As the bronze cools it shrinks about 1/4" for every 12". The ceramic shell cracks and is not reusable, for every casting in the edition you must go back to the rubber mold for another wax casting and start the process all over again. The shell is knocked off with a hammer and chisel and the casting is cleaned usually by sandblasting.