Talc is dusted over lasts to help uppers slide over during lasting and to aid removal of the last when the shoe is done. Talc may also help prevent stray adhesives from sticking to the last.
Some makers prefer to rub their lasts with dry soap.
Procurement
Talc is widely marketed as a body powder, but usually mixed with other materials and perfumes. Pure talc can often be had in pure form as a cosmetics ingredient or as marketed for automotive tire shops or fiberglass filler.