  The superheating that usually occurs when a solid is melted by volumetric
heating can produce irregular solid-liquid interfaces. Such interfaces can be
visualised in ice, where they are sometimes known as Tyndall stars. This paper
describes some of the experimental observations of Tyndall stars and a
mathematical model for the early stages of their evolution. The modelling is
complicated by the strong crystalline anisotropy, which results in an
anisotropic kinetic undercooling at the interface; it leads to an interesting
class of free boundary problems that treat the melt region as infinitesimally
thin.
