Page:On the economy of machinery and manufactures - Babbage - 1846.djvu/104

70 Operations of copying are effected under the following circumstances:

(83.) The art of printing, in all its numerous departments, is essentially an art of copying. Under its two great divisions, printing from hollow lines, as in copper-plate, and printing from surface, as in block-printing, are comprised numerous arts.

(84.) Copper-plate Printing.In this instance, the copies are made by transferring to paper, by means of pressure, a thick ink, from the hollows and lines cut in the copper. An artist will sometimes exhaust the labour of one or two years upon engraving a plate, which will not, in some cases, furnish above five hundred copies in a state of perfection.

(85.) Engravings on Steel.This art is like that of engraving on copper, except that the number of copies is far less limited. A bank-note engraved as a copper-plate, will not give above three thousand impressions without a sensible deterioration. Two impressions of a bank-note engraved on steel were examined by one of our most eminent artists, who found it difficult to pronounce with any confidence, which was the earliest impression. One of these was a proof from amongst the first thousand, the other was taken after between seventy and eighty thousand had been printed off.