Step 16 - Pouring the Bronze Alloy
The bronze alloy used in many modern foundries is made mostly of copper with trace amounts of silicon and other elements. The bronze alloy is delivered to the foundry in the form of ingots or bricks.
This bronze alloy can be heated in a furnace to various temperatures but never lower than 1900°F when preparing to be poured. Once molten, the bronze is carefully poured from a crucible into the heated ceramic shell. When the bronze has cooled, a couple hours later, the ceramic shell is "devested" or removed to expose the bronze cast.
Step 17 - Welding and Finishing
Once the different parts of the sculpture are poured they are welded together. The metal is "chased" by grinding down unwanted metal and sandblasted and buffed to remove any lines and imperfections. Once the metal chasing process is complete the artist is invited back to inspect the bronze sculpture. Photographs of the original clay sculpture are used to make sure that the bronze is an accurate reproduction.
Step 18 - Patina
A patina is color that is applied by heating up the metal and applying various chemicals. Three water soluble chemicals form the basis for most patinas: Ferric Nitrate produces reds and browns, Cupric Nitrate creates the greens and blues and Sulphurated Potash produces black.
Bronze patination is an art form in itself. Ms. Mongeon often watches and gives artistic direction in the patination process. Once completed the bronze sculpture is ready for delivery and installation.
The art foundry that I use is:
Art foundry - Houston, Texas
Contact Scott at 713-686-5567
(More about the mold making process can be found on the artist's forum and in the online Newsboy Journal.)