Sentence:  his quill drawings had a scratchiness , suggesting skin texture ; the clay he used plastically to suggest soft moving flesh , as in an abdomen , in a reclining torso ; the wax he smoothed over to give the body <WSD>surface</WSD> an elastic pull . 
Meaning of the word marked with <WSD> tags:  the outer boundary of an artifact or a material layer constituting or resembling such a boundary