[Tony Pro]

To get the soft edges in clothing or any soft transition, I follow what Sargent did, which was use a few transitional strokes of a middle value between your foreground element and your background, usually by bristle filbert, than move to a mongoose hair brush and soften some of the passages to get a real lost edge.

By the way, I have seen that Sargent that you posted. It taught me VOLUMES on his method. I think its for sale in a gallery in New York...