I did the series using a gouache resist technique on 500lb arches cold press paper.
I drew out all my lines onto the paper, and then depending on the area, I either painted everything but the lines (all the large white spaces/negative space areas) or painted the lines (the details in the faces).
After waiting for the gouache to completely dry, I dabbed waterproof ink with a brush across the whole surface.
Then waited for the ink to dry. Once the ink is completely dry, I run the paper until the faucet. The result is that the ink on top of the gouache flakes off, while the ink directly on the paper surface stays unharmed.