Henry Cohen, numismatist and bibliophile, published in 1870 with Rouquette a Guide de l'amateur de livres à vignettes du XVIIIe siècle, which successive editions (1873, 1876, 1880, 1886) expanded and retitled livres à gravures. The 6th edition, "revised, corrected and considerably enlarged" by Seymour de Ricci in 1912, is the one everyone cites: a substantial volume set in two columns, arranged alphabetically by author, in which every illustrated edition is given its collation, the list of its plates and engravers, its states, its large-paper issues, and notable copies sold at auction with their prices.
Cohen is cited by column: "Cohen, 302" refers to column 302 of the 1912 edition, where the edition is described. The reference guarantees that the edition exists, that it is illustrated, and that its complement of plates is known; it allows one to verify that a copy is complete with its plates, to identify a proof before letters or an added suite, and to place a paper or binding among the copies cited. It does not guarantee the conformity of the copy in hand, which must be collated plate by plate, nor the completeness of the states, which sale catalogues have continued to specify.
The limitations stem from its date: the prices are those of 1912, some engraver attributions have since been corrected, and provincial or foreign editions with French plates are treated unevenly. Cohen is supplemented by Portalis and Béraldi for engravers, by Brunet and Tchemerzine for texts, and by the catalogues of major twentieth-century sales for choice copies. A notice that cites Cohen without collating the plates cites a promise, not a description.
