Photo: How does window frost form such fanciful patterns?

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Also known as fern frost or ice flowers, here's how Mother Nature does some of her most delicate work.

Few things are as intricate and ephemeral as frozen water crystals, whether they take the form of snowflakes, frost, or other. One particularly beautiful type is the frost that forms on windows, like this fabulous example photographed by Corrie White.

But how in the world does a pattern like this come to be?

We found the answer from Kenneth G. Libbrecht, a physicist at California Institute of Technology (Caltech) who studies the molecular dynamics of crystal growth. He explains:

Window frost forms when a pane of glass is exposed to below-freezing temperatures on the outside and moist air on the inside. Water vapor from the air condenses as frost on the inside surface of the window. The picture at right shows a patch of window frost about the size of an outstretched hand. Window frost often makes elaborate patterns as the crystal growth is strongly influenced by the window surface. Scratches, residual soap streaks, etc., can all change the way the crystals nucleate and grow.

Libbrecht also says that window frost is less common nowadays since there are fewer single-pane windows around; the improved insulation of double-pane windows hampers the growth. Thankfully, we have pretty photos like this that we can linger over.

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