Sentence:  `` I paint the nothing '' , he said once to Franz Kline and myself , `` the nothing that is behind the something , the inexpressible , <WSD>unpaintable</WSD> ' tick ' in the unconscious , the ' spirit ' of the moment resting forever , suspended like a huge balloon , in non time '' . 
Meaning of the word marked with <WSD> tags:  not paintable especially not suitable for artistic representation on canvas