Ice flowers are the structures of ice which form on single-layer glass windows during frost. Warm humid air on one side of the window pane will cool and sublimate ice crystals, which grow into flower-like structures. Since the surface is very flat and usually also very clean, the sublimation process goes slow, and the resulting ice structures can be very beautiful. Any scratch or other inconsistency in the glass surface will be a nucleation source for ice growth. The ice flowers can even show invisible cleaning marks on the glass by their oriented growth pattern.

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