Instabilities arise on the solidification front of a melt when the solid grows into an undercooled melt sufficiently fast. For controlled experiments the sample is pulled through a temperature gradient towards the undercooled side.
Experimental results by the group of A. Libchaber on the nematic-isotropic transition of a liquid crystal.
With increasing pulling speed the instability becomes stronger:
Transition to a time-dependent state of localized drift waves:
(A. Simon, J. Bechhoefer and A. Libchaber, Phys. Rev. lett. 61 (1988) 2574)