Etching, Engraving, & Intaglio Printing. Anthony Gross. Oxford University Press. (A favourite printer and artist of Suzanne's)
How to Identify Prints, Bamber Gascoigne. Thames and Hudson.
Manual of Etching and Engraving, Walter Chamberlain, Thames and Hudson.
Processes of Graphic Reproduction in Printing, Harold Curwen. Faber & Faber.