Nature printing is a process whereby a natural object is somehow used directly to create a print (HERE).
Below is a nature printed image of an Oak Fern (Polypodium Dryopteris) from a book by Thomas Moore (1821-1887) - The Ferns of Great Britain and Ireland; Edited by John Lindley. Nature-printed by Henry Bradbury. London: Bradbury and Evans, 1857.
A digitised copy of the book is available HERE.