Of Talbot's photographic engravings, Larry J. Schaaf writes:
The first clearly identifiable photogravure process was laid out in Talbot's patent No. 565, titled Improvements in the Art of Engraving; he filed the preliminary specifications on 29 October 1852 and finalized them on 24 January 1853. The patent consisted of producing a photographic image on a metal plate, using this image as a resist to control the etching of that plate, and then printing the resulting plate using a conventional printing press and standard printer's ink. He restricted his description to steel plates, mentioning in passing that zinc plates or lithographic stones might also be used, but notably he made no reference to copper plates at this time.1
Copper was only introduced as an option in 1858 when Talbot patented his modified photogravure process, the photoglyphic engraving.
1 Sun Pictures, Catalogue 12, New York, 2003, pp.8-9.