Fern Frost

March 26, 2011


Photographer: John W. Ehman
Summary Author: John W. Ehman

Window frost, sometimes called fern frost, can form on windowpanes when the air outside is very cold and the air inside is moist. The outside air temperature on the winter's day when this photo was snapped was 15 degrees F (-9 C) and the inside air temperature was 66 F (19 C). Crystal formation is affected by surface features of the glass, like dust and dirt particles, which serve as nucleation points for crystalline growth. Towels had been left to dry near the old and weathered bathroom window shown here provided just the right level of moisture conducive to frost formation. If there had been considerably more moisture in the air, for instance after a steamy shower, or if the windowpane had not been extremely cold, the water vapor would have merely formed ice or water droplets on the glass. The very low temperature of the glass allowed the moisture to go directly from a gaseous state to a solid state -- in the form of frost. Photo taken on January 22, 2011 in Upper Darby, Pennsylvania.

Photo Details: Camera: Panasonic Lumix DMC-G1; Lens: Leica Macro-Elmarit; Focal Length: 45.0mm (35mm equivalent: 90mm); Aperture: f/9.0; Exposure Time: 0.017 s (1/60); ISO equiv: 100. The dark background was created by a large Yew bush.