He was a painter, but his best works are perhaps wood-engravings.
I find that are masterly, among these, the series "Intimacies": wood cut slices of life, mostly of couple life.
Images are dominated by thick black spaces (the artist has to scoop out the white
areas in xylography).
But this black background makes even clearer the "pictures" that Vallotton takes in the rooms of private lives, where he pitilessly catches psychological moments and intercourses between charachters.
Iris for you