A microscopic variation in composition within the grains of a metal casting due to failure to achieve equilibrium during solidification. Coring is often seen in cast bronzes that solidify with a dendritic structure. The individual dendrite arms have centres that have higher concentrations of copper than the outer portions, which have higher concentrations of tin. The chemical difference within the dendrites gives rise to increased corrosion attack. Coring is different from interdendritic corrosion, where the tin-rich eutectoid between the dendrite arms is attacked preferentially.