Intaglio. 

"Stone Rabbits", by Ralph Slatton

Intaglio printing is based on slightly different principles than most other printing methods.  The basic concept is to etch a metal plate, then the ink is pushed into the etched areas and then excess ink is wiped away leaving ink only in the recesses.  The block is then printed under extreme pressure forcing the ink from the plate on to the paper, this also will leave permanent marks on the paper, proving it is an original print verses a computer print. 

Intaglio printing is an incredibly long process, it is also an expensive process.  However it is a very long lasting and durable form of printing. 

I have done hand etched Intaglio prints.  Using a metal scribe I scratched the surface of a piece of copper.  Using a very thick black ink, I used newspaper to rub the ink deep within the recesses.  When printing you must soak the paper before hand.  This will help to suck the ink from the thin ridges of the plate.