  The crucial role of hydrodynamic pinch-off instabilities is evidenced in the
coarsening stage of viscous liquids. The phase separation of a barium
borosilicate glass melt is studied by in-situ synchrotron X-Ray tomography at
high temperature. The high viscosity contrast between the less viscous phase
and the more viscous phase induces a topological symmetry breaking: capillary
breakups occur preferentially in the less viscous phase. As a result,
contrasting morphologies are obtained in the two phases. This symmetry breaking
is illustrated on three different glass compositions , corresponding to
different volume fractions of the two phases. In particular, a fragmentation
phenomenon, reminiscent of the end-pinching mechanism proposed by Stone et al.
[1, 2] is evidenced in the less viscous phase.
