Although those things were called “mimeographs”, technically a Ditto machine is different from a Mimeograph. see here, for instance:
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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. You 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 you put the stencil on the drum wrong-side-out, your 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.
I, too, remember that Proustian odor for the ditto copies. Wiki says that:
But, c’mon. isopropanol is just rubbing alcohol, and I’ve worked with methanol often enough without fume hood (or gloves). I think the warning is overblown.
More here on the differences: