Ice flower

Ice crystals in a plant-like shape

An ice flower is an ice crystal that is said to be similar to a plant or a flower because of its shape . It is a special form of hoarfrost . Ice flowers typically appear on windows , but they can also appear on other surfaces.

Emergence

Scattered patterns of purely hexagonal ice flowers

Appearance of the English fern frost (' Fern -Eis') called ice flowers with purely dendritic growth

Ice flowers typically appear on the inside of thin window panes in heated rooms when the outside temperature sinks below 0 ° C, and correspond to the tarnishing (fogging) of the panes without frost: If the thermal insulation of the window is low, the inner window surface cools due to the significant temperature difference by conduction below freezing point. Warmer room air that flows to the pane cools down. The air's ability to absorb moisture also decreases with temperature . If the air temperature falls below the dew point , the air can no longer hold the water vapor so that it precipitates on the colder surface. If the internal temperature of the pane is below freezing point, the water resublimates (freezes). If there are nuclei or nuclei on the glass, the water can crystallize in many ways . Over time, the ice flowers typically grow from the lower edges and can cover the entire disk. The reverse is less common, for example outside air at above zero degrees sweeps over surfaces that have previously been cooled below freezing point, the structures are created on the outside, for example overnight on cars when the weather changes.

Ice flowers are flat crystals of water. Usually hexagonal (flower-like) shapes, which are based on hexagonal symmetry (as with the snowflake ), mix with dendritic , tree-like branched growth. The exact processes are not yet fully understood. In addition to dust particles, germs are also tiny scratches on glass or a surface coating that provide floral shapes, but also, for example, the wiping patterns from window cleaning, car windshield wipers, paint polishing, and the like. Changes in temperature by half a degree or in humidity by half a percent noticeably affect the type of growth. Under other circumstances, the windows often only ice up to form cloudy amorphous ice ( rough ice ) or largely translucent clear ice . If the ice flowers continue to freeze, they are covered by thicker ice sheets that are also more or less transparent and gradually disappear.

Tarnishing windows and ice flowers are typical indicators of poorly insulating windows. Thanks to modern windows, ice flowers have become a rare phenomenon in domestic homes today. Structurally harmful are not the ice flowers themselves, but rather that when thawing, the water seeps into the window and frame joints and can lead to frost or moisture damage and mold formation.

Sea ice flowers

A shape similar to the ice flowers are sea ice flowers , spatial shapes that arise in spring and autumn in the Arctic and Antarctic. Similar dendritic crystallization structures can be observed during the spontaneous freezing of supercooled liquids and other processes, but the formation of the six-pointed symmetrical shapes is characteristic of water.

A special optical phenomenon of the flat ice crystals is that here - for example with the polarized sky light and a polarization filter - the birefringence of ice can be observed, which occurs in all other directions apart from the main axes of the sixfold symmetry.