Hmm, that video was a nightmare of music overplaying the narration and an "Oh sh*t" overdub coming in.

Not working for me!
Anyway, your explanation above is thorough. About what I'd heard, as far as a process that requires patience and a light touch. It really looks gorgeous when done well, and yours is gorgeous. I would imagine that the repetitive nature of the wash/sand/repeat process is enjoyable and calming. I have used rubber cement for masking with hand coloring - works like a charm, and cheap!