A mold is a form used to shape hot glass for casting or blowing processes. Molds are made of metal, stone, wood, rubber, graphite, plaster, earthenware, and other materials. Some molds (e.g., dip molds) impart a pattern to the parison (unshaped mass of glass), which is then withdrawn, and blown and tooled to the desired shape and size; other molds (sometimes known as full-size molds) are used to give the object its final form, with or without decoration. Dip molds consist of a single part and are usually shaped like beakers. Full-size molds usually have two or more parts and can be opened to extract the object.
William Gudenrath Demo: Optic Mold Cup using dip mold
Chunk Casting into plaster mold from Glassmaking Processes