Good safety gear is a must. Goggles that can handle the heat, welding gloves, respirator.... the main risks are fumes and flying molten metal so dress appropriate. This is not a safe process and i don't recommend you do it!
1. The bust built in wax. note the vent from the chin and the large reservoir to get a mass of metal pushing in.
2. nails are put in to make blind vents.
3. Plaster is painted over the entire piece and then the nails are pulled.
4. after pulling the nails it is wrapped in rags soaked in plaster. and a small can is attached to make an easy spot to pour.
5. the can is cut to allow for the wax to flow out and the can is put in the boiling water.
6. a coffee can holds the heat on the mold. The wax that flows out needs to be constantly removed to stop it from exploding with steam under a continuous surface of wax.
7. The wax burned out a little longer over the fire
8. video of the pour. The zinc from Rotometals is heated in a normal can that food comes in. it is bent with pliers to make a nice spout. As you can see the burnout was inadequate and lead to a metal volcano.
9. after the pour some wax was not burned out and caused steam to prevent full filling of the mold.