Diagram depicting a version of the main steps in sand casting:
1) a chef-modèle or pattern is a specially designed model for sand casting made of a hard material—often metal—to withstand the repeated handling and ramming of sand within a multipart, stacked metal or wooden frame called a casting flask;
2) the pattern is buried about halfway in backing sand in a first section of the flask called the cope; piece mold sections are built up over the model with carefully rammed special casting sand whose naturally occurring binder, clay, helps the compacted sand to hold the desired shape;
3) once the exposed part of the pattern is covered with mold pieces, the second section of the flask, or “drag,” is affixed to the cope and the piece molded side is back filled with carefully rammed sand;
4) the tightly packed flask is flipped; the cope and backing sand, now on top, are removed to provide access for a similar piece molding process to be performed on the other side of the chef-modèle;
5) the two-part casting flask is parted and the mold pieces carefully disassembled to remove the pattern;
6) to make a hollow cast, a core must be created to define the thickness of the bronze walls; this is made by ramming the same special casting sand into the hollow impression left by the chef-modèle; metal core supports are incorporated into the new sand; the cope and drag are joined, thereby creating a sand replica;
7) the flask is opened again and the sand replica is removed and shaved down evenly overall to form the core; white areas indicate hollow spaces for metal to fill; the thin legs in this case will be solid, and so will not need a core;
8) the sand mold and core are baked, then carefully reassembled in the cope and drag; the core supports projecting from the core serve to suspend the core in place; channels are cut strategically into the mold to ensure the efficient distribution and flow of the metal and venting of air;
9) the cope and drag are reassembled and locked together, and the metal alloy, which has in the meantime been liquefied, is poured into the mold;
10) once the metal has solidified and cooled, the sand mold is broken open and the bronze cast removed; the metal sprues that have formed in the channels are cut off; and the surface is cleaned and repaired as needed;
11) if a bronze is cast in numerous sections, or separately from a base, it will be joined at this stage. The final steps may consist in refinishing of the metal surface and coloration through the application of a chemical patina or some form of coating.
Diagram based on Charles Marion Russell (American, 1864–1926), Medicine Whip, modeled 1911, sand cast 1912–16, H. 14.8 cm (Gilcrease Museum, Tulsa, 0837.14). See Case Study 6.