Lost wax casting is a process of creating a metal object by making a wax model, encasing it in a heat resistant material, melting away the wax to create a single use mold, and pouring molten metal into the cavity left behind to create a metal object. The mold is then broken to reveal the object created. The metal object is then cleaned up.

“Lost wax” refers to the fact that your original wax carving is destroyed during the mold making process. I usually do direct lost wax (described below) rather than indirect lost wax. An nice overview of how indirect lost wax is done is here, from the National Gallery of Art in Washington, DC.

1. Design Stage: First, I come up with an idea for what I want to make. I like to sketch and refine my ideas on paper. A full design may include multiple parts and require a variety of techniques (in addition to the lost wax casting) to create the final object.
2. Model Making: Next, I make a model of the design using a material like clay or wax. For lost wax casting, I carve my design in a special type of wax called “casting wax.” This wax is easy to sculpt and can capture fine details.
3. Add Sprues: Small channels called sprues are attached to the wax model and the mold. These channels will allow the wax to melt out, and the molten metal to fill the resulting mold. The wax model and sprue assembly is called a “wax tree”, as it resembles a tree (wax model) with branches (sprues). The wax tree will create the shape of the mold into which molten metal will be poured during the casting process. Note: Not having enough sprues or not having them in the proper location can cause your piece to not turn out.
4. Calculating Metal Amount Needed: Before melting the metal, calculate the amount needed to fill the mold. This is estimated by weighing the wax model and sprues. Multiply this by the metal density (specific gravity) of the metal you are using. Metal shrinkage during cooling is also a factor to consider in this calculation.
5. Attach Sprue Base: After weighing the waxes, attach the sprue base, or button, to the model. The sprue base is where the sprues are attached to the mold. This also creates a small reservoir for molten metal to flow into the rest of the mold that will be created once the wax is burned off. After casting, this piece and the other sprues will be removed on the final piece.
6. Encase Wax Model in a Mold: The wax model with all sprues attached (wax tree) is then encased in a heat-resistant material like plaster or ceramic slurry. This embedding part of the process is called “investment”. Once the investment material hardens, it forms a rigid mold around the wax tree. Later, the wax is melted or “lost” from the mold, leaving behind a cavity in the shape of the desired object, into which molten metal can be poured. This typically involves a form (like a cylindrical flask) that I put the wax tree into, then fill with a liquid investment material. This material needs to dry before the next step. Note: Modern castings tend to make use of a man-made vacuum to force any air bubbles out of the liquid investment material. These air bubbles can cause all sort of problems with the casting.
7. Burn Out the Wax: The investment (wax tree surrounded by the hardened heat resistant material) is heated until all the wax is burned off.
8. Melting Metal: Metal, such as bronze or silver, is heated until it reaches its melting point. This usually is done in a furnace or kiln to be able to reach the necessary temperatures, but can be done in other ways. Different metals have different melting points, so the temperature must be adjusted accordingly.
9. Pouring Metal: Once the metal is completely melted and reached the desired temperature, it is carefully poured into the empty mold through the sprues. The mold is often preheated to prevent the metal from solidifying too quickly. Note: Modern castings tend to make use of a man-made vacuum to force the molten metal into the tiniest detail of the original model.
10. Cooling Down: The metal cools and hardens inside the mold, taking the shape of the design and the sprues. Depending on the metal and mold, you quench the piece after a few minutes (while red hot) or an hour or so later. Note: Quenching is a heat treatment process used to rapidly cool a material, typically a metal or alloy, from a high temperature. This rapid cooling is usually achieved by immersing the material in a quenching medium such as water, oil, or brine. Quenching alters the internal structure of the material, resulting in changes to its mechanical properties, such as hardness and strength. It is commonly employed to harden metals and alloys.
11. Breaking the Mold: Once the metal has cooled completely, break the mold to reveal the metal object with sprues. I sometimes find the item didn’t turn out the way I wanted, so I end up melting it down and starting again. If it did turn out, I continue on to the next step.
12. Removing Sprues: The metal object, still attached to the sprues, is removed from the mold. Using shears or snips, cut the metal at the sprue attachment points. Grinders may be needed to remove excess metal.
13. Finishing Touches: The metal object will likely have rough edges or imperfections from the sprues and/or casting. Once the majority of the sprue material is removed, sandpaper or sanding tools can be used to smooth out any rough edges or remaining marks left by cutting or grinding. Then, the surface can be polished to match the finish of the rest of the object.
14. Adding Details: Additional details or decorations can be added at this stage. This could mean engraving, adding patina or attaching other parts, etc. Niello would be added at this stage.
15. Final Inspection: The piece is inspected one last time to make sure everything looks right.

Wax Laurel

Wax annular brooches carved for class samples

Wax of Backward-Looking Bird Brooch

Wax buckle, carved from hard wax (designed for carving, ready to move forward with the casting process

Buckle plate, built using flat sheet wax.

Strap end wax with silver pieces in place to test fit