What is the Name teachers used for those mimeograph copies that had purple ink?
Ditto machine
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The duplicator that produces purple copies is NOT a mimeograph. It
is a spirit duplicator (called alcohol process duplicator in
Europe). It does not use ink. It uses a master. The master consists
of a sheet of paper attached to a special (usually) purple carbon
paper. It also uses spirit fluid (methanol in U.S.; ethanol in
Europe)>
In the US it was often called a Ditto machine. Ditto was one
manufacturer of these machines. I have also heard it called a
Rexograph--after another manufacturer. This type of machine was
also made by A.B. Dick, Heyer, Roneo, Standard, etc.