Not only is “adumbration” a mighty fine word, it’s also one of the most important stages of a painting. For depth and shadow I usually use ink of varying dilution.
Happily, too, R2 looks less as though he has been painted by an 8-year old.
Perfection doesn’t exist, or if it does, then it’s extremely subjective. I believe this is the closest to “happy” I’m going to get with this painting.