Lost Wax Process for Bronze Casting

The lost wax process for creating bronze sculptures is thousands of years old (pieces 6000 years old have been found in the ancient Mesopotamian and Egyptian regions). Also known as “investment casting”, this method of art was widespread in Europe until the 18th century. Although bronze sculptures are still being done, they are often through a foundry. I had the challenge and pleasure of learning the lost wax process and pouring several of my own pieces.

Sculpting in Clay

Each sculpture starts with a clay original. This piece was done in WED (Walt Disney Clay) with a metal armature inside. Painstakingly sculpted by hand this can take 1 to 3 weeks to complete depending on the subject.

I also use plasticine/plastelina (Roma Clay) which is oil based and never dries. I sometimes work also in polymer clay.

Once the sculpture is completed they must be sealed with shellac or acrylic sealant to prepare for molding.

Creating a Mold

From the clay original sculpture, a mold is made. They are often separated into several “sections”. The first layers are liquid rubber and the outer layer is hard “mother mold” which is composed of plaster or other hard mold materials. This process takes 1 to 2 weeks to complete.

Create a Wax Copy

Next a wax copy is created from the mold. Jeweler’s wax (very hard) is used so the piece is detailed, workable, but durable. The finished piece is hollow with the wax 1/4 to 1/2 inch thick.

Sprue the Wax piece

Sprue: a channel through which metal or plastic is poured into a mold.

The Sprue has to include a pour point (cup), lines for pouring into the mold, and vents for the air to escape back up. The sprues can be either direct (as shown) or indirect.

The sprue system is in wax also, and is time consuming and an art unto itself. It may also include cutting the sculpture into “segments”.

Creating the Bronze Sculpture

Breakout, Welding and Chasing

The bronze is broken out of the ceramic shell with sledge hammers, air-tools, chisels and hammers. Then the piece is cleaned and welded back together. Next the bronze sculpture must be “chased” using grinders, sanders, dye grinders with metal bits and Dremel tools to clean, repair, smooth and correct details lost in the casting process.

Sandblasting and Patina

The sculpture is then sandblasted, polished, sanded, and checked over for any final corrections or changes. Finally patina is added; chemicals that react with the bronze like “liver of Sulphur”. The bronze sculpture must be heated and the patina is applied “hot” by spraying or painting it on and then torching it. The sculpture needs to be waxed or sprayed with a sealant afterwards.