The first impressions of an engraving. India-proofs are those taken off on India-paper. Proofs before lettering are those taken off before the plate is sent to the writing engraver. After the proofs the orders of merit are—(1) the prints which have the letters only in outline; (2) those in which the letters are shaded with a black line; (3) those in which some slight ornament is introduced into the letters; (4) those in which the letters are filled up quite black.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
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