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.

As cited in: Joseph Beuys, Dia Art Foundation. Joseph Beuys, Dia Art Foundation, 1988. p. 23 ; Statement about the 'Rubberized Box' by Joseph Beuys, 1957 - Interviews with Caroline Tisdall, 1974 & 1978