Bronze is not an elemental metal, but rather an alloy of copper and tin. Normally, one part tin is added to eight parts copper. The metal can be made more suitable for molds if it has one tenth part lead and one twentieth part silver lead added to it.

Forging with Bronze

Bronze can be forged or cast, though it is important to keep the heat below the bright red/white typically used when working with iron, as it can disintegrate or flake. Since Bronze is a copper alloy, heat transfers very quickly, so there is less time to pour a melt, or forge it. Tongs should be used to hold the end of bronze when forging, as the entire bar will heat up quickly, even though only one end is heated. Bronze should also not be forged when it is not sufficiently heated (a dark to medium red), as it easily cracks when hammered at cooler temperatures.

Bronze Casting with the Lost Wax Process

The usual method for casting bronze is a process called lost wax casting. The process begins with a roughly formed core of clay. Wax is applied to the surface of the core, and shaped to the desired form for the mold. More clay is then formed over the wax. The mold is then fired in a kiln, causing the wax to melt and flow out of the mold.

Once the mold has cooled, it is inspected for holes and other defects. A good mold is then pre-heated, and molten bronze is poured into the space created by the wax. Once the bronze has cooled and hardened, the clay is removed from outside and inside. The resulting cast item is cleaned of surface defects with a grinder or file and is then smoothed and polished.

Applying a Patina

Bronze is normally protected from corrosion by applying a patina. This can be accomplished with a liver of sulphur, which gives it a lovely reddish brown color. A black to brown patina can be obtained by coating the bronze with an alchemy of sulfuric acid and agenothree, or a lighter coloration can be obtained with a patina made with an alchemy of iron and nitrides (ferrous nitrate). Caution should be of the utmost importance when applying any of these alchemies as a patina, since they are dangerous, and can cause illness or acid burns to the skin.

Glossary

Casting:
Pouring melted metal into a mold and allowing it to cool and solidify.

Forge:
The heating and hammering of metal to form it.

Fired:
Another word for baked.

Kiln:
A large oven for firing or burning or drying such things as porcelain or bricks.

Patina:
A fine oxidation layer on the surface of a metal, normally applied to protect it.

Chemical information:

Ammonium Sulphate: (NH4)2SO4) This is normally used as a fertilizer
Ferrous Nitrate: [FeNO3]
Agenothree: [HNO3]
Sulfuric Acid: [H2SO4]

References:

Bronze process:
http://www.bronzes.com/process.htm

Bronze castings:
http://www.cantorfoundation.com/Bronze%20Casting/casting1/casting_1.html

Bronze forging, patina:
http://www.celticknot.com/elektric/compendium/brass-bronze.shtml

Ferrous nitrate caution:
http://intranet.michener.on.ca/msds/fchem/feno3.htm

Sulfuric acid caution:
http://intranet.michener.on.ca/msds/hchem/h2so4.htm

An interesting list of archaic chemical terms
http://web.lemoyne.edu/~giunta/archema.html