False-colour scanning electron micrograph (SEM) of a specimen of magnesium oxide ceramic showing the effects of rapid heat-treatment with a laser beam. The smooth grains at bottom have a well-sintered microstructure; the powder from which the ceramic is made has compacted together at a temperature below its melting point. Above, the ceramic has been melted by the laser beam. The granular region consists of small crystals that have grown only a little due to rapid cooling. At top, more prolonged melting & slower cooling has produced grains with a dendrite structure. Magnification: x75 at 35mm size. Yellow tint. Ref: MICROCOSMOS, fig. 7.9, page 130.