marcus' techniques

Pouring molten bronze into an investment mold.

Marcus’ bronze sculptures are cast using the “lost wax” method. In this process, he transforms the original sculptural shapes into thin (3/16”-thick) “wax shells” by using molds. The wax shells are then encased in plaster or ceramic m​olds, heated to remove the wax, and the “lost” wax is replaced with molten bronze.

He then chases and finishes the metal pieces. For a large sculpture, this includes welding together the pieces. Then Marcus applies a patina, followed by a wax or lacquer final protective coating. New and experimental sculptures were cast in his own foundry (which was dismantled in 2008); commissioned works are cast in various commercial art foundries in the New York-Massachusetts area.

Bob uses a few different techniques to get to the “wax shell” stage. Some of his bronzes are “clones” of sculptures he originally carved in stone, some are created in clay or plaster, and others are created by molding directly from live models.

The first two techniques---cloning his other sculptures or creating forms in clay or plaster---use rubber molds, from which he casts the wax shells.



One of the more interesting techniques for producing molds from live models is a process Marcus learned from a 1979 visit to George Segal’s studio in New Brunswick, New Jersey. A five-sheet stack of wet plaster gauze is molded over a body part--such as an arm--of a live model. Five minutes later the stiff yet pliable mold is removed from the model, and a 3/16”-coat of heated wax is applied to the inside the mold. After the wax cools, the solid wax piece is removed. Finally, all the wax body parts are assembled to form the completed figure.

The figure is then cut into six or seven sections, and each section embedded into a final mold. Marcus used “investment” molds made of plaster and sand, which he heated in a kiln for 2-3 days at 1150° F to burn out the wax; commercial art foundries use “ceramic shell” molds, which require a much shorter heating period. In another furnace, bronze is melted (above 2000° F) and then poured into the mold, which has “lost” the wax and is now empty. The bronze pieces are re-assembled by welding, the metal is chased and finished, a patina is added to the finished sculpture, and the finished sculpture is given a protective coating.

Chatham, MA 02633

r marcus sculpture

Plaster molds made from various parts of the model’s body for the sculpture “Sunburst”.

​r marcus sculpture

The sculpture “Sunburst” in wax, ready to be cut into sections and sent to the foundry.