spirit master
A two-ply sheet used in a spirit duplicator, in which the top sheet could be typed, drawn, or written upon, and the second sheet was coated with a layer of colored wax.
spirit master: the inked template for hectograph printing
A spirit master is a two-ply carbon sheet designed for use in spirit duplicators, the offset printing machines common in offices and schools from the 1930s through 1980s. The top ply is ordinary paper that accepts typewriter keys, ballpoint pen, or pencil marks. The bottom ply is coated with a thin layer of colored wax (typically purple, but also available in blue, red, or black). When you strike the top sheet, the pressure transfers a reverse image of the colored wax onto the underside of the top ply, creating the printing surface.
The master sheet is mounted on the drum of a spirit duplicator with the wax-coated side facing outward. As the drum rotates, it passes under a dampening roller that applies a small amount of spirit solvent (usually a mixture of methanol and water, though modern versions used safer solvents). The liquid temporarily dissolves the wax coating, transferring the colored layer onto each sheet of paper that presses against the drum. A typical spirit master can produce 100 to 300 legible copies before the wax coating is depleted.
Variants and limitations
Spirit masters came in different sizes to match standard paper formats. Multi-color masters allowed the operator to produce different colored images by using separate wax coatings on the same top sheet, though registering multiple colors was imprecise. The key drawback was image quality: spirit duplicators produced fuzzy, low-contrast prints compared to offset lithography. The colored wax also meant that originals were difficult to correct. Erasure and retyping could be done, but usually left visible ghosting.
The term 'spirit master' reflects the solvent used in the process. The master sheet itself held no ink in the modern sense; instead, it stored a waxy pigment that was selectively dissolved and transferred during printing. This made it fundamentally different from mimeograph stencils, which were punched sheets, or offset masters, which used photographic emulsion. Spirit duplicators became standard in schools because they were cheap, fast, and required minimal training, but they have been almost entirely replaced by photocopiers and digital printers since the 1990s.