"Urstoff" was one of the many technical terms the young Primo Levi came to 
admire in his apprenticeship as a chemist and poet.  In his memoir THE PERIODIC 
TABLE, Levi recalls his sense of wonder (searingly unironic, even in retrospect) 
at the German language's clarity in expressing the nature of the universe--in 
this case, the primordial chemical stuff out of which everything is made.  My 
own sense of wonder over Levi's own language, shared with pianist Aaron Shorr, 
inspired this little duo for him and Peter, which was later adapted into a piano 
concerto for Aaron.  =