Lost Wax Bronze Casting Processes 9

Lost Wax Bronze Casting Processes 9 - 13

Lost Wax Bronze Casting Processes 9 - 13

10) The ceramic shells are reheated in the kiln, which hardens the ceramic patches. At the same time, bronze is being smelted in a crucible in a very hot furnace. When the bronze has reached the appropriate temperature, the ceramic shells are removed from the kiln and placed cup-upwards into a tub filled with sand, or stood upright in some other manner. Of course, workers involved in this part of the process must wear layers of protective gear against the potential of being burned. Carefully, the crucible filled with liquid bronze is lifted from its furnace and the metal is poured into the ceramic shells. It is important that the shells are also highly heated during the pouring, or the difference in temperatures would shatter the shells. The bronze-filled shells are allowed to cool.

11) Now the ceramic shell is "lost" as well as it is hammered and/or sand-blasted off of the bronze. The cup and sprue system, which are also faithfully recreated in bronze, are cut off. They will be re-melted and become part of the next series of bronzes.

12) In a similar manner as the wax copies were "chased," the bronze copies are also worked on until the tell-tale signs of the casting process are removed, and the sculptures again look like the original artwork. Metal-chasing usually consists of filling any pits, which were air bubbles in the molten bronze, and recreating the original surfaces where feeder or vent tubes had to be attached.

13) When the bronze copies have been perfected, they are colored to the artist's preference using heat and chemicals which change color when they are painted onto the surface of the reheated bronze. This coloring is called patina, and is often green, black, white or brownish to simulate the surfaces of ancient bronze sculptures. (Ancient bronzes gained their patinas from oxidation and other effects of being on Earth for many years. Yes, this may include chemical changes from pigeon droppings.) However, many artists prefer that their bronzes have brighter, paint-like colors. Today, these effects, too, can be achieved through the application of patina chemicals rather than painting the bronze. Patinas are less opaque, generally, than paint, and this allows the luster of the metal to show through. After the patina is applied, a coating of wax is usually applied to protect the surface. Some patinas change color over time because of oxidation, and the wax layer slows this down somewhat.