Frost on a window pane can take many forms. Often a sequence of events can be deduced from the resultant patterns. The very fine crystals are formed first and appear almost uniformly over the entire area. Sunlight melts regions at the top of the window. The droplets make clear patterns down the glass. When the sun goes down the pane freezes over again - but this time the presence of ice crystals ready to grow and liquid water has produced much larger and dramatic results as shown in the photograph.