The brass is melted directly (without a crucible) in the melting chamber of the furnace. The chamber is constructed so that its floor slopes downward toward a horizontal tap hole at its lowest point. During the melting process, this hole is plugged from the inside by a tapered iron plug sealed with fire clay. When it is time to run the bronze into the mold, an iron "crook" is pushed into the tap hole from the outside. The crook has a narrow point that shoves the plug into the furnace (where it floats to the top of the bronze). Behind the point, the crook has a tapered swell that follows the point into the hole, and, because of its shape, seals it. The flow of the bronze is then controlled by pulling the crook back out of the tap hole, retracting the swell from the narrowest point of the hole and opening it up.

The amount of bronze to be poured is calculated by a combination of volume and weight. Bronze weighs about 500 pounds per cubic foot (with variations depending upon the exact alloy). The volume of the mold can be roughly calculated using basic geometry. That can be converted to the weight of bronze required and that is a guide for how much to melt. The trick is to melt a bit more than needed, and, if necessary, run off any excess into an area near the mold designed to receive it. In the case of our mortar pour, we had just the right amount--a combination of stunning calculation and even more good luck!

Photographs of the pattern (or "model") making process can be found in "About the Project" section of this blog. It involves building up the shape of the casting around a tapered wooden spindle, wound with rope, covered with "loam" (a mixture of clay, sand, and other ingredients) and then wax. The final details are cut into the wax as it is turned using a "strickle," an iron tool cut to the desired profile. Afterwards, features such as the trunnions and flash pan are added. Once that is done, the model is then covered with more loam and built up until there is a shell around it.

Once it is dried, as you see in the posted photos, the tapered wooden spindle is pulled out, the rope follows, and the inside of the resulting hollow is heated. This melts the wax and the remains of the model can be removed, leaving a hollow in the shape of the desired casting. This mold is then buried vertically in the ground next to the furnace tap hole. A fireclay ramp is constructed from the tap hole to the open top of the mold, and, as the video shows, the molten bronze runs from the tap hole directly into the mold. Once the bronze has solidified, the mold is lifted out of the ground, and broken off the casting. This destroys the mold, and each casting therefore requires the remaking of the model and mold (processes that get faster as we gain more experience).