Spirit duplicator copies, are often referred to as "ditto" copies, which was a brand name. Spirit duplication was considered an evolution of the hectographic print process. Invented by Wilhelm Ritzerfeld in 1923, spirit duplication became a common and economical printing method for limited quantities of copies in the context of offices, classrooms, clubs, or churches. Many early fanzines were produced this way. Instead of an ink-transmitting gelatin pad as used in the hectographic process, spirit duplication incorporates a waxy, paste-like ink that is partially dissolved with the application of a hydrocarbon spirit solvent, materials which later were understood to be unsafe.
