Answer:
Printmaking.
Explanation:
After some research, I went to https://artmuseum.princeton.edu/collections/objects/5480
and in the medium section, it showed aquatint.
According to Wikipedia, "Aquatint is an intaglio printmaking technique, a variant of etching that produces areas of tone rather than lines. For this reason it has mostly been used in conjunction with etching, to give both lines and shaded tone."
