How can a cast keep a carving’s shape?

A museum visitor can stand beside a full-sized copy of a carving whose original is far away. The copy can preserve the depth of a curl, the ridge of a leaf or the hollow between two shapes. Casting transfers this three-dimensional surface through a carefully made mold.

A mold takes the opposite shape of the surface it touches. Where the carving sticks out, the mold has a hollow. Where the original surface dips inward, the mold can project into that dip. This reversed surface is sometimes called a negative. It holds the spaces that the original shape occupied.

Casting material fills the mold's hollows. A plaster mixture can flow into details before setting into a solid. When the mold is removed, the new cast has projections where the mold had hollows. Reversing the shape a second time brings back the original pattern of high and low places. A complicated sculpture may need a mold made in several sections so those pieces can be removed.

The cast is a new object even when its shape closely follows the original. Plaster is different from the original stone or metal. Mold seams, finishing, paint and later repairs can affect what a viewer sees. Records of when and how a cast was made help people judge which details it preserves and which belong to the copying process.

Copies can also become evidence. The Victoria and Albert Museum describes casts whose originals have since suffered damage or weathering. A surface detail that faded outdoors may remain in a cast made earlier. The copy does not replace every kind of information in the original, but it can carry a record of its former shape across both distance and time.