Proof impression

one of the early impressions taken from an engraving, before the plate or block is worn.
See under Impression.

See also: Impression, Proof

Webster's Revised Unabridged Dictionary, published 1913 by G. & C. Merriam Co.
References in classic literature ?
A teaboard, cups and saucers, plates, knives and forks (including carvers), spoons (various), saltcellars, a meek little muffin confined with the utmost precaution under a strong iron cover, Moses in the bullrushes typified by a soft bit of butter in a quantity of parsley, a pale loaf with a powdered head, two proof impressions of the bars of the kitchen fire-place on triangular bits of bread, and ultimately a fat family urn: which the waiter staggered in with, expressing in his countenance burden and suffering.
While normally the artist first worked-up the face of his sitters, a handful of proof impressions of this print are worked-up in every detail except the face.