A little left field, just came up in a discussion.
When I was in a journalism class way back in 1963 or so, I saw some pieces of a paper mache sheet type material with the right-reading impression of set type on them. They must have been proofs, but why they were done this way rather than as an inked strike-off, I don't know.
Does anyone out there in TSB-land know more than I do about this?
