"The outward appearance of every object I make is the equivalent of some aspect of inner human life.. .My feelings then had this special kind of darkness – almost black like this mixture of rubber and tar. It is certainly an equivalent of the pathological state mentioned before, and expresses the need to create a space in the mind from which all disturbances were moved: an empty insulated space."
January 1, 1970
https://en.wikiquote.org/wiki/Joseph_Beuys