Lost Wax Bronze Casting

An illustrated review of our lost wax bronze casting process.

First we modeled the pieces we wanted to cast out of modeling wax.  The wax becomes malleable when heated - we heated metal tools over an open flame and applied to wax.  We each cast three pieces.  My goal was to make a pair of earrings.  The form is that of a samara (the fruiting structure of a maple tree, shown with the modeled wax above).

A mold is constructed for each of the wax forms.  In this process we create a plaster mold in a tin can.  A metal rod is inserted in the bottom of our wax form and into a mound of clay.  The clay mound will become the well for the wax to melt.  Then the form is coated with a thin coat of plaster to insure the fine details are preserved. 

Surround form with can and seal with modeling clay.  Fill form with plaster.  Allow plaster to set about an hour.

Turn over dried mold.  Remove clay mound.

Use pliers to remove rod.  The mold is allowed to fully dry (about 4 days).  Then the molds are fired in an electric kiln, I think to cone 4, and the wax melts out of the form.

The mold is removed from the kiln when it has cooled to about 200 degrees.  The mold is inserted into this tub of sand to keep it stable while heating.  A couple of bronze nuggets are placed into the well and heated with the blow torch until they begin to bubble.

Bronze nuggets.

Once the bronze turns liquid heat is removed and the top of the mold is plunged to force the bronze down into the mold.  The bronze and mold is then allowed to cool.

Cooling bronze.

The process is very time sensitive, everyone in the class had a different job they were responsible for.  Two casting stations were set up.  About 40 molds were cast in 2 hours.

Cooled molds.

Bronze nuggets.

Once the forms are cooled you knock out the plaster mold.  Because bronze is much stronger than the plaster there is no danger in damaging the bronze form while destroying the plaster around it. 

Only one form was successfully cast out of three.  I guess no earrings!  Bronze castings are always a risky venture.  Sometimes the bronze only partially fills the form if not properly plunged.  1 out of 3 seemed to be the class average... to finish the piece you scrub off the remaining plaster, and I would have sawed off the stem I added at the top to cast the form and drilled a small hole to attach to the earring.  This was a really interesting process... despite the poor results.  It amazes me that an artist could invest so much with such risk of failure.  I guess the same could be said of ceramics...