A spirit duplicator (also referred to as a Ditto machine in the United States or Banda machine in the United Kingdom) was a low-volume printing method used mainly by schools and churches. It was also used by members of science fiction fandom and early comic book fandom to produce fanzines. Sheets printed on such a machine were sometimes called ditto sheets, or just dittos in the U. S. (an example of a genericized trademark). The term “spirit duplicator” refers to the alcohols which were a major component of the solvents used as “inks” in these machines. They are sometimes confused with the mimeograph, which is actually a different technology.
The duplicator used two-ply “spirit masters”. The first sheet could be typed, drawn, or written upon. The second sheet was coated with a layer of wax that had been impregnated with one of a variety of colorants. The pressure of writing or typing on the top sheet transferred colored wax to its back side, producing a mirror image of the desired marks. (This acted like a reverse of carbon paper.) The two sheets were then separated, and the first sheet was fastened onto the drum of the (manual or electrical) machine, with the waxed side out.
There is no ink used in spirit duplication. As the paper moves through the printer, the solvent is spread across each sheet by an absorbent wick. When the solvent-impregnated paper comes into contact with the waxed original, it dissolves just enough of the pigmented wax to print the image onto the sheet as it goes under the printing drum.