I love some of the images made by Italian photographer Ugo Mulas (1928-73) in his Verification-series. They are in the 1990 catalogue 'Ugo Mulas' by Germano Celant, ed. Rizzoli NY. The most striking is Verifica 7 - Il laboratorio - Una mano sviluppa l'altra fissa - A sir John Frederik William Herschel - 'The laboratory. A hand develops, the other prints. To Sir John Herschel (...)' It shows a black hand on a white sheet and vice versa. One hand dipped in developer and one in fixer etc.
photograms
[my polagrams]

It was dedicated to John Herschel another hero of mine, who invented fixer on jan 29th or feb 1st 1839. And by doing so invented modern photography.
-Herschel said "Let me have this one for a few minutes" and after a short time he returned and gave the picture to Mr Fox Talbot saying "I think you'll find that fixed" - Herschel also gave us the words positive and negative. The word photography is generally ascribed to him, but Niepce used this one for the first time in a letter to his brother.
Maybe Mulas even knew that Herschel invented, among a lot of other things, the finger-printing identity system as well.