Lost Wax Casting

Lost Wax Casting is a simple process with a worldwide history that dates back almost as far as history itself. It is one of the most basic processes for casting, and is still in use to this day. Here is a short video covering the process as used in an industrial setting.

The video is a good overview of the process, but here are the steps laid out in a little more detail for a smaller project.

1. The first step is obtaining a wax positive, either by sculpting your original in wax, or from a mold of some kind.

2. Once you have the positive, the next step is to create a sprue and vent system. Sprues when added correctly allow for the metal to more easily reach parts of the mold, such as an extended arm on a figure, that would otherwise be difficult to reach. Vents allow for a flow of air out of the mold to prevent bubbles from forming and ruining your cast. The sprue and vent system is topped with a cup, to create a resevoir to hold any excess metal that is poured into the mould, and to add some pressure to allow for the metal to fill out the mold.

3. Once your wax positive is ready to go, its time to shake and bake, you dip your wax into a chemical slurry, and then cover it with ceramic sand, rinse and repeat. The trick with the slurry is to not form bubbles in the coating, and to get a thin but viscous layer on your wax. When applying the ceramic sand is to make sure to get the sand into all the fine details, or you will lose them in your mold.

4. When the ceramic shell has dried, your mold is now placed in a kiln upside-down and fired. This serves a dual purpose, first it hardens the ceramic shell, and warms it to high temperatures so it will not crack on contact with hot metal, and secondly to drain the wax out of the bottom. (In many kilns this can be collected and used again.) Some foundries use a separate firing for the draining, and hardening of the ceramic shell.

5. The final step in the casting process is to pour the metal, a metal pour requires a team of people working together, and is itself a complex process. However for small scale items (A small piece of jewlery for example) , you can do this yourself, with a smaller scale furnace. (They even have competitions for micro-furnaces that could fit in your hand when they aren’t hot.)

6. The very last step is just to break of the shell with a hammer, then clean and finish your piece by sawing off the sprue, then filing and polishing your finished piece.

Although commonly used for metal, as described above, the lost wax casting process can be used with just about any material that can be poured into the empty shell of a wax mold. (Usually just a plaster mold, when you aren’t pouring something molten hot.)

While pouring metal isn’t an option in most classroom settings, much of the rest of the process, of making a wax sculpture, then creating a mold from it, are excellent things to learn and can be done at many levels with kids. Paticularly connecting how artists affect industry (Which is in your state goals.)  and in ideas of making multiples. When looking for lesson ideas, one can draw from a wide range of information as well, as this is a process used in many cultures, finding a relevent example for your students requires only a little history research.

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