Grain growth has long been studied primarily by the examination of sectioned, polished and etched samples under the optical microscope. Although such methods enabled the collection of a great deal of empirical evidence, particularly with regard to factors such as temperature or composition, the lack of crystallographic information limited the development of an understanding of the fundamental physics.  Nevertheless, the following became well-established features of grain growth:
# Grain growth occurs by the movement of grain boundaries and also by coalescence (i.e. like water droplets)
#Grain growth competition between Ordered coalescence and the movement of grain boundaries
# Boundary movement may be discontinuous and the direction of motion may change suddenly during abnormal grain growth.
# One grain may grow into another grain whilst being consumed from the other side
# The rate of consumption often increases when the grain is nearly consumed
# A curved boundary typically migrates towards its centre of curvature