Aquatint -

: Perhaps the most famous proponent, Goya used aquatint to create the haunting, atmospheric backgrounds in his Los Caprichos series.

The hallmark of aquatint is the use of a porous, acid-resistant ground to create "pockets" that hold ink. The process typically involves the following steps: How are etchings and aquatints made? | Artistic Techniques aquatint

Throughout history, several masters have utilized the technique to profound effect: : Perhaps the most famous proponent, Goya used