Sentence:  He could no longer build anything , whether a private residence in his Pennsylvania county or a church in Brazil , without it being obvious that he had done it , and while here and there he was taken to task for again developing the same airy technique , they were such fanciful and sometimes even playful buildings that the public felt assured by its sense of recognition after a time , a <WSD>quality</WSD> of authentic uniqueness about them , which , once established by an artist as his private vision , is no longer disputable as to its other values . 
Meaning of the word marked with <WSD> tags:  an essential and distinguishing attribute of something or someone