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A spirit duplicator (also referred to as a Ditto machine in North America, Banda machine in the UK or Roneo in France and Australia) was a printing method invented in 1923 by Wilhelm Ritzerfeld and commonly used for much of the rest of the 20th century. The term "spirit duplicator" refers to the alcohols which were a major component of the solvents used as "inks" in these machines. The device coexisted alongside the mimeograph.
Spirit duplicators were used mainly by schools, churches, clubs, and other small organizations, such as in the production of fanzines, because of the limited number of copies one could make from an original, along with the low cost and correspondingly low quality of copying.
The spirit duplicator was invented in 1923 by Wilhelm Ritzerfeld. The best-known manufacturer in the US and the world was Ditto Corporation of Illinois, while copiers available in the UK were commonly manufactured by the Block & Anderson company, under their "Banda" brand. In both cases the trademark became a generic name for both the copiers and the process in their respective markets.
Spirit duplicator technology gradually fell into disuse starting in the 1970s after the availability of low-cost, high-volume xerographic copiers. By the turn of the 21st century, the use of the technology was rare. The technology remains useful where electrical power is unavailable, or where the only remaining originals of legacy documents requiring duplication are in "spirit master" form.
In 20th century folk memory
The faintly sweet aroma of pages fresh off the duplicator was a memorable feature of school life in the spirit-duplicator era. A pop culture reference to the aroma can be found in the 1982 film Fast Times At Ridgemont High. At one point a teacher distributes a duplicated schedule of class quizzes, and every student immediately lifts it to his or her nose and inhales. The blues band Saffire - The Uppity Blues Women has another perspective in their song "School Teacher's Blues," which has the lines, "My fingers have turned purple, My master's like I chewed it, My mind is getting warped from inhaling Ditto fluid."
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 first sheet transferred the colored wax from the second sheet to the back side of the first sheet, producing a mirror image of the desired marks. This produced the same result of a sheet of carbon paper put in backwards. The two sheets were then separated, and the first sheet was fastened onto the drum of the machine, with the back side out. This acted like a printing plate.
There is no separate ink used in spirit duplication, as the wax transferred to the back side of the first sheet contained the ink. As the paper to be printed moved through the printer, the solvent was spread across each sheet by an absorbent wick. When the solvent-impregnated paper came into contact with the back side of the first sheet, it dissolved just enough of the pigmented wax to print the image onto the paper as it went under the printing drum.
The usual wax color was aniline purple (mauve), a cheap, moderately durable pigment that provided good contrast, but masters were also manufactured in red, green, blue, black, and the hard-to-find orange, yellow, and brown. All except black reproduced in pastel shades: pink, mint, sky blue, and so on.
Spirit duplicators had the useful ability to print multiple colors in a single pass, which made them popular with cartoonists. Multi-colored designs could be made by swapping out the waxed second sheets; for instance, shading in only the red portion of an illustration while the top sheet was positioned over a red-waxed second sheet. This was possible because the duplicating fluid was not ink, but a clear solvent.
The duplicating fluid typically consisted of a 50/50 mix of isopropanol and methanol, both of which were inexpensive, readily available in quantity, evaporated quickly, and would not wrinkle the paper.
In 1938  a nonflammable solvent was invented by Johan Bjorksten to allow the possibility of using electrically driven machines with out the concern of the flammability of pure methyl/ethyl alcohol. "A composition composed of 10% of monofluoro tri-chloro methane and 90% of a mixture of 50% methyl alcohol, 40% ethyl alcohol, 5% water and 5% of ethylene glycol mono-ethyl ether. This solvent mixture is non-flammable in the closed space of the reservoir and has a flash point of 100°F. when fully exposed to air. The solvent mixture has a pleasant odor, reduced toxicity and gives at least as good copies as the duplication liquid before the addition of the mono-fluoro tri-chloro methane. It is believed that the high efficiency of mono-fluoro tri-chloro methane as a flame reducing agent is due to the fact that its boiling point is sufficiently low as to cause the formation of a non-flammable vapor, film on the surface of the organic solvent, with sufficiently high boiling point as to be substantially retained by the solvents even at high summer temperatures."
This process worked best with cheap, lightweight paper stocks, but when the sheets of paper were impregnated with the solvent they could easily crease or crumple, jamming the machine. One well-made master could print about 500 copies before the pigment was exhausted and the print became illegible. If fewer copies were required, the master could be removed from the printing drum and saved for future use.
Dittoed copies now pose a serious challenge to archivists responsible for historic document and artistic preservation. Dittoed images gradually fade with exposure to ultraviolet light, limiting their usability for permanent labels and signage. When exposed to direct sunlight, ditto copies can fade to illegibility in less than a month. The low-quality paper often used would yellow and degrade due to residual acid in the untreated pulp. In the worst case, old copies can literally crumble into small particles when handled.
- Eric Zorn (January 16, 2007). "That ditto high is harder and harder to duplicate". Change of Subject column. Chicago Tribune. Archived from the original on 2013-10-23. Retrieved September 6, 2013. "'[D]itto,' a word -- and a smell -- that snaps many of us right back to our youth."
- "Nonflammable Solvent". U.S. Patent Office. Patent No. 2,254,469 Published in: 1941.
- M P Doss, Information Processing Equipment (New York, 1955)
- Irvin A. Herrmann, Manual of Office Reproduction (New York, 1956)