  Deep polarimetric Westerbork observations of the galaxy cluster Abell 2256
are presented, covering a frequency range of 325-377 MHz. The central halo
source has a diameter of the order of 1.2 Mpc (18'), which is somewhat larger
than at 1.4 GHz. With alpha=-1.61+/-0.04, the halo spectrum between 1.4 GHz and
22.25 MHz is less steep than previously thought. The centre of the ultra steep
spectrum source in the eastern part of the cluster exhibits a spectral break
near 400 MHz. It is estimated to be at least 51 million years old, but possibly
older than 125 million years. A final measurement requires observations in the
10-150 MHz range. It remains uncertain whether the source is a radio tail of
Fabricant galaxy 122, situated in the northeastern tip of the source. Faraday
rotation measure synthesis revealed no polarized flux at all in the cluster.
The polarization fraction of the brightest parts of the relic area is less than
1%. The RM-synthesis nevertheless revealed 9 polarized sources in the field
enabling an accurate measurement of the Galactic Faraday rotation (-33+/-2 rad
m^{-2} in front of the relic). Based on its depolarization on longer
wavelengths, the line-of-sight magnetic field in relic filament G is estimated
to be between 0.02 and 2 uG. A value of 0.2 uG appears most reasonable given
the currently available data.
