Duplicating machines were the predecessors of modern document-reproduction technology. They have now been replaced by digital duplicators, scanners, laser printers and photocopiers, but for many years they were the primary means of reproducing documents for mass distribution.
Like the typewriter, these machines were children of the second phase of the industrial revolution which started near the end of the 19th century (also called the Second Industrial Revolution). This second phase brought to mass markets things like the small electric motors and the products of industrial chemistry without which the duplicating machines would not have been economical. By bringing greatly increased quantities of paperwork to life the duplicating machine and the typewriter gradually changed the forms of the office desk and transformed the nature of office work.
They were often used in schools, where cheap copying was in demand for the production of newsletters and worksheets, and self-publishers used these machines to produce fanzines.
The mimeo machine (mimeograph) used heavy waxed-paper "stencils" that the typewriter cut through. The stencil was wrapped around the drum of the (manual or electrical) machine, which forced ink out through the cut marks on the stencil. The paper had a surface texture (like bond paper), and the ink was black and odourless. A person could use special knives to cut stencils by hand, but handwriting was impractical, because any loop would cut a hole and thus print a black blob. If the user put the stencil on the drum wrong-side-out, the copies came out mirror-images.
The ditto machine (spirit duplicator) used two-ply "spirit masters" or "ditto masters". The first sheet could be typed, drawn, or written upon. The second sheet was coated with a layer of colored wax. 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.
The usual wax color was aniline purple, a cheap, durable pigment that provided good contrast, but other colors were available. Unlike mimeo, ditto had the useful ability to print multiple colors in a single pass, which made it popular with cartoonists. One well-made ditto master could at most print about 500 copies—far fewer than a mimeo stencil could manage.
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