Lost Wax Casting

Lost wax casting, also known as cire perdue (French for “lost wax”) is a method that has been used for centuries to make many of the intricate metal objects we see in museums today.

“People used this technique all over Europe, Asia and North Africa. It was used by the Sumerians in 2500 BC when bronze was first discovered. It was then used in Shang Dynasty China (1700 BC) to make goblets for sacrifices to the gods and in medieval Europe (1200 AD) to cast the bells for the cathedrals. Lost-wax casting seems to have been independently developed in West Africa around 900 AD, too.”

Lost wax casting is used to make objects in metal that can’t be made any other way because of how complex the form is. Wax is used to make a model of whatever object you want to ultimately be made from metal.

Wax models can be made by hand and then cast to make one object or a mold can be made to produce multiple copies of the same form.

Once the wax model has been touched up and is ready for casting, the first step the form undergoes (and the most important) is spruing. Spruing is a process in which sprues (wax rods) are permanently attached to your wax model which will provide paths for molten metal to flow and for wax to escape.

The sprued model must then be secured to the bottom a steel tin flask, keeping in mind that there must be ample room between the model and the walls of the can (about a half an inch from the top and a half an inch on the sides).

The next step is pouring in the investment. Investment is a type of plaster that won’t burn or crack when subjected to the extremely high temperatures that molten metal can get up to. The investment is mixed with water to form a slurry which is poured into the can to completely submerge the wax model.

The can with the sprued wax model and the slurry is placed in a debubblizer which sucks the air bubbles up to the surface of the investment so that when the model is cast there won’t be any cavities formed by bubbles.

The can is placed in a kiln to undergo the burn-out process. After this, all that remains of the original model is a negative space inside the hardened investment. Now molten metal can be injected into these spaces in the investment that were once occupied by wax.

Once the injected metal hardens, the cast piece must now be released from the can. This can be done by hammering or sandblasting the investment away.

The final cast piece will be dull and have many imperfections. The last process then is to polish the piece.

Since I have not actually cast something yet, I’m not sure if what I have written here is correct. This is a summary of my notes from class, some books and some websites on lost wax casting. As the semester goes on and I learn more about casting, I will edit this post.


Sources:
1. http://users.lmi.net/drewid/Lost_Wax_Casting.html
2. http://en.wikipedia.org/wiki/Lost_wax
3. http://www.encyclopedia.com/doc/1E1-cireperd.html
4. http://www.historyforkids.org/learn/arts/lostwax.htm
5. Modeling in Wax for Jewelry and Sculpture, 2nd Edition by Lawrence Kallenberg