Each mask required many weeks of work on the part of Woods, and other surgeons who followed his lead. A plaster cast was taken of the subject's wounded face – but only after the wounds and subsequent surgeries had totally healed. The crude process was itself a trial. The plaster cast was used to make a squeeze of plastocene or clay. This disfigured bust was used as the foundation of all prosthetic restorative work, with the sculptor working to replace the missing components of the face with the shapes from the opposing side. The mask itself was made from a thin copper sheet – galvanized copper to facilitate painting after forming. Painting a realistic portrait onto the copper mask was as challenging as the sculpting: each was finished while the patient wore it, in order to most accurately match the tone of the flesh with the enamels.