MARC21       007m'12  Base of film
     Values: 
             Safety   base
              a   Safety base, undetermined
              c   Safety base, acetate undetermined
              d   Safety base, diacetate
              p   Safety base, polyester
              r   Safety base, mixed
              t   Safety base, triacetate
                  Nitrate
              i   Nitrate base
              m   Mixed base (nitrate and safety)
              n   Not applicable
              u   Unknown
              z   Other