In practice, most castings solidify with a dendritic structure. The tendency for dendrites to grow in certain crystallographic directions affects the grain structure of castings. When liquid is poured into a mould, initial contact with the (cold) mould walls usually results in nucleation of a large number of crystallites (small crystalls). This forms the so-called chill zone. Solidification occurs from each of these crystallites, with the dendrites oriented in the corresponding easy growth directions.

Growth occurs more rapidly from crystals which have an easy growth direction parallel to the heat flow direction i.e. normal to the mould wall.

Less favourably-oriented crystals grow more slowly and tend to get pinched off by the more rapid growth of their neighbours.