Sentence:  Through 1911 and 1912 , as the Cubist facet-plane 's tendency to adhere to the literal surface became harder and harder to deny , the task of keeping the <WSD>surface</WSD> at arm's length fell all the more to eye-undeceiving contrivances . 
Meaning of the word marked with <WSD> tags:  the outer boundary of an artifact or a material layer constituting or resembling such a boundary