Science Why hardly any ice flowers grow even in the cold
Graceful twigs, fern leaves and flowers also grow in winter: In sub-zero temperatures, ice flowers form on some glass panes. But this once common cold splendor has become rare.
08.02.2025, 06:12
SDA
"Thanks to the good insulation of modern windows, the inner pane of glass no longer reaches sub-zero temperatures," explains physicist Max Gmelch. In the past, this was often the case with leaky or poorly insulated window panes.
In principle, several conditions must be met for ice flowers to occur: a cold surface below freezing point, sufficiently high humidity in the room and condensation nuclei, i.e. unevenness on the surface, such as dust particles or cracks. However, the former in particular can only be found in very old houses or perhaps in a stairwell, says Gmelch, who heads the SAOT graduate school at Friedrich-Alexander-Universität Erlangen-Nürnberg.
"So we have the warmer indoor air, which cools down at the window surface. This reduces its ability to store water - but this water has to go somewhere," he says. "It usually settles as moisture on the pane, it condenses." However, if the window is particularly cold, the water vapor in the air changes directly from a gaseous to a solid state without first becoming liquid. "This is called resublimation."
Ice crystals need starting points
In order for an ice crystal to form, a condensation nucleus is required, i.e. a point where the crystal can attach - a dust particle or a crack. "More water likes to attach itself to the first crystal, so it continues to grow. As disks are not completely flat, the hexagonal crystals do not simply continue to grow hexagonally, like snowflakes. "A wide variety of structures can result," says Gmelch.
Ice flowers rarely form on car windows. The lower temperature of the windshield - in contrast to a house - plays a role here, explains the expert. "This allows the water vapor to resublimate much faster and in many places at the same time." For the formation of ice flowers, however, it is important that the process progresses slowly, growing from individual nuclei.
Gmelch explains that the process observed in ice flower formation also has applications in technology. "Nowadays, glasses are anti-reflective coated so that no disturbing light reflections impair vision. The manufacturing process is very similar: a material is vaporized, which is deposited on the lens and forms this anti-reflective layer." In microelectronics and semiconductor technology, warm materials are also applied to cold surfaces in this way.
