Observations of the water vein system in polycrystalline ice

The geometry of the vein system in ice has been investigated using photographs of enlarged veins in ice samples that were grown in the laboratory. The veins, which are non-uniform, act as tiny triangular-shaped, water-filled prisms that refract the light passing through them.

The three vein widths in the cross-section of a vein can be deduced from two photographs taken from different directions. The dihedral angle along a given vein edge can be observed directly by viewing it at a node, where four veins meet, from a particular direction. The dihedral angles range from 25-degrees +/- 1-degrees to 105-degrees +/- 1-degrees. It is shown that the vein cross-section can be constructed, given the three widths of a vein and one of the dihedral angles, providing that the radius of curvature around the vein walls r(v) is a constant. This assumption can be checked if the values of at least two of the dihedral angles associated with the vein cross-section are known. If r(v) is a constant, then the solid-liquid interfacial energy gamma(sl) must be isotropic for the veins in question and any deviations from uniform equilibrium geometry must derive primarily from anisotropy in the grain-boundary energy gamma(ss). The cross-sections of three veins that meet in a particular node are constructed. The assumption of isotropic gamma(sl) is found to hold for this node.