A spirit duplicator or ditto machine was a low-volume printing method used mainly by schools and churches. The technology fell into disuse with the availability of low cost, high volume xerographic copiers starting in the 1970s; few spirit duplicators remained in use by 1985, although they remained popular through the early 1990s in applications such as printing cross country race results for events which took place away from electrical power sources.

The spirit duplicator was invented in 1923 by Wilhelm Ritzerfeld .

The duplicator used two-ply "spirit masters" or "ditto masters". The first sheet could be typed or hand-written upon, while the second had an waxy inked surface that impressed a mirror image of the desired marks onto the back of the front sheet. (This acted like a reverse of carbon paper.) The front sheet was then torn off and wrapped around the drum of the (manual or electrical) machine, with the back (inked, reverse) side out.

The usual ink color was purple (generally an aniline-based dye) because it provided the best contrast, but there were also a few other colors—"red" was more of a pink, "green" was mint, "blue" was aqua. Multi-colored designs could be made by preparing different parts of the master with different colored carbon/inking sheets, because the pungent-smelling duplicating fluid (typically a 50/50 mix of isopropanol and methanol) was not ink but a clear solvent. This fluid, spread across each sheet by an absorbent wick, dissolved just enough ink to print the sheet as it went under the printing drum. The paper was slightly slick or shiny, and the slightest crease or crumple in it could jam the machine. Ditto masters could make about 500 copies before the print quality became unreadable, not as many copies as a mimeo stencil could.

Spirit duplicators were inexpensive and well suited to the short runs useful for school worksheets or church newsletters. They owe most of their popularity to their relative ease of use, and later, to the lack of a requirement for an external power source. Even the least technically-minded teachers, professors, and clergy could make use of them.

Print quality was generally poor, though a capable operator could overcome this with careful adjustment of feed rate, pressure, and solvent volume.

The hectograph was an earlier technology which used a gelatin pad to transfer ink from a master to the copies.

Mimeograph machines predated the spirit duplicator, and had lower cost per impression and much better print quality. But mimeographs required handling of messy ink, and fell out of favor for casual use.

The thermofax machine was introduced by 3M in the late 1960s and could make a spirit master from an ordinary typewritten or handwritten sheet. The resulting print quality was abominable but the machines were still popular because of their convenience.

See also: Duplicating machines.

Source(s):

• The Dead Media Project

• M P Doss, Information Processing Equipment (New York, 1955)
• Irvin A. Herrmann, Manual of Office Reproduction (New York, 1956)
• W B Proudfoot, The Origin of Stencil Duplicating (London, 1972)