The Art of Foundry Work, that of melting and casting of metals into shapes and forms, is a rare and difficult art to accomplish. The process requires intention, strength, methodology, and the willingness to press the boundaries of ones skills. The use of vastly different of materials and specific, and expensive machinery, can rarely be accomplished by a single practitioner. There are few foundries which still exist in the world today, and even fewer schools which teach such arts.
There are only a small handful of casting methods. Each processes requires pouring melted metal into a mold. Molds can be made of high-heat plastic, sand, or a fabricated cement/ plaster mixture. The Lost Wax method holds the greatest versatility when it comes to achieving a desired shape and design, and makes use of the cement/plaster mold method.
The first major hurdle in working in casting has nothing to do with metal but with wax. The process begins with shaping the desired works, that of the final piece or shape itself, out of wax. Wax is a difficult medium in itself, as it acts like clay in that you can remove or add as needed. You’ll specifically need casting wax for this, which is harder than candle wax and burns away cleanly. Additionally, you’ll also be required to work with hot tools, such as knives and scrapers, kept warm over an open flame, to shape the wax.
Once the desired shape is created, more often than not hollow in its design for weight consideration, armatures of wax are affixed with intentional placement so that a funnel effect occurs at one side of the piece. The concept is very much that of a well, where wax will flow out of one end, and metal into the same end to pool. The mouth of the well will need to be wide enough for liquid access, and the armatures will need to connect smoothly to ensure full access to all parts of the wax shape. Be sure to add at least one armature to extend out from the bottom of the piece, separate from and level with the mouth of the well, to be used as a sort of pressure valve.
The entire piece is then wrapped in chicken wire, or woven wire, to create integrity for the shell which will be formed around the piece. The wrap should be close but not snuggle. An inch wiggle room around the wax piece is fine. A framed wood box is then constructed leaving an additional few inches clearance around the wire shape. You want close fitting but again, not snug. The wooden does not need to be fancy but it should be sturdy to keep shape. The frame is then internally lined with a material like cardboard. You want something that can be easily destroyed, and will also hold water. Place the wire structure containing the wax shape inside the wooden structure with the mouth of the well and the valve armature faced up. A mixture of cement, plaster, and water is then mixed together and poured into the wooden frame, submerging the wire/wax structure with the mouth of the well and valve exposed. The entire piece should sit and cure for at least a day.
Once dry, remove the wooden frame and cardboard sheathe. You should basically have a block of cement with two wax arms sticking out of the top. It’s important to ensure that the cement block has no other holes in it or cracks, as molten metal will aim to escape. The block is then attached upside down to a pulley system and hoisted so the funnel arms face the ground. The piece is placed in a kiln which typically fires from the sides and has a base with a basin to catch the wax. The idea is that the heat from the kiln will melt the wax out of the block onto the ground leaving a hollow imprint of the desired shape inside. This is your mold. If done correctly the armatures should have made clear paths through the piece so that all the wax is removed. This process can take a few hours to achieve temperature, and then another few hours to cool down for handling.
Using the pulley system the block is lowered to the ground, flipped right side up, and moved to a casting well – typically a sunken sandbox build for this purpose. The walls and floor of sandbox are typically cement. A hole is dug into of the sand box and the mold is submerged, well facing up, so that the well is just below the level of the sands surface. Use the sand to create a wide funnel shape around the mouth of the well, carefully avoiding pouring any sand into the hallow of the mold. Molten metal will be poured into the funnel of the well and should pipe up through the armature valves if all has been done correctly.
At this point you’ve worked with wax, wire, wood, cement, plaster, pulleys, kilns, and sand. Needless to say, casting is an event! Foundry work up onto this point is long and hard, but not altogether expensive. Plaster, sand, clay, wire… all these things are relatively cheap. Even the kiln can be made with brick and wood, if desired. The costliness of casting comes next in two parts: The metal itself is relatively expensive, around $36 USD for a half pound, and the foundry itself, which melts the metal.
Foundry work is often done with bronze or aluminum because the melting point of each metal is low, around 950 °C or 1,742 °F . Aluminum is a bit lower at 660.32 °C or 1220.58 °F . It makes them both relatively easy to work with. A foundry itself is basically a jet engine sunk into the ground with a hollow hole in the middle. A rotating fan of flames encircles a hollow, run on gas. One is effectively trying to run a stove at 2000 °F, meaning it puts off a great deal of heat. Protective safety gear from head to tow is an absolute must at this point, as a person can’t even approach said tool any closer than 3 feet.
A stone crucible is sat into the hollow of the foundry and brought up to a temperature of around 500 °F. A metal ingot of either cast bronze or aluminum is placed into the crucible and brought to its melting point. A steward, at this juncture, will stir the metal and drag out any impurities which rise to the surface, dumping them with a steel or iron ladle into the sand pit. Once the metal is at temperature two workers in safety gear with giant tongs will lift the crucible of melted metal out of the foundry and pour the metal into the mouth of the well in the sand. There is an art and technique to this. One must not spill.
Typically a group of casts are done at once and the steward aims to melt only enough metal for what’s needed. It’s not ideal to cast a piece in two parts, and if it appears that a cast will be under filled the steward may opt not to cast it, but to return the crucible to the foundry and melt more metal. Typically ingot shapes will have already been pressed into the sand box for any excess metal left over in the crucible. This will form small ingots for future use.
The casts are then left for a few hours to cool.
Once at handling temperature the molds are recovered from the sand box and moved to a work station where the plaster/cement will be removed with sledge hammer, wire form included – don’t worry, its hard to hurt the piece within. At this point one will have the exposed shape originally done in wax, now before them in metal. The armature will then need to be removed, and a process of grinding and sanding will commence to bring the piece into its desired finished form.
The entire process can easily take up to a month, and requires the skills and attention of an entire team. Though the process can be hard and challenging, the over all product is immortal, and that, in itself, is worth the effort.