Sentence:  Although there is no question but that the process of washing fabrics involves a number of phenomena which are related together in an extremely complicated way and that these phenomena and their interrelations are not well understood at the present , this section attempts to present briefly an up-to-date picture of the physical chemistry of washing either fabrics or hard <WSD>surfaces</WSD> . 
Meaning of the word marked with <WSD> tags:  the outer boundary of an artifact or a material layer constituting or resembling such a boundary