  We perform fracture experiments on nanoscale phase separated glasses and
measure crack surface roughness by atomic force microscopy. The ability of
tuning the phase domain size by thermal treatment allows us to test thoroughly
the predictions of crack font depinning models about the scaling properties of
crack surface roughness. It appears that in the range of validity of these
depinning models developed for the fracture of brittle materials, our
experimental results show a quantitative agreement with theoretical
predictions: beyond the characteristic size of disorder, the roughness of crack
surfaces obeys the logarithmic scaling early predicted by Ramanathan, Ertas and
Fisher (PRL97)
