How a frosty windshield becomes a work of art
Have you ever noticed that frost sometimes creates interesting patterns on windshields and windows?
Brenda Main caught intricate patterns on her windshield in Kentville, N.S., this week — capturing what’s called window frost, but often referred to as fern frost or frost feathers due to its appearance.
This frost formation is quite unique and needs specific conditions to form.
How does frost form in the first place? It must be cold and humid, and the most common cause is from deposition where gas changes to a solid state without becoming a liquid. In this case, water vapour turns to ice crystals. Frozen dew from condensation can also be considered frost.
In this case, we’re concerned with deposition because the associated ice crystals that organize and branch out are considered fractal — which simply means complex geometric objects or patterns that are selfsimilar at different scales.
For fern frost, conditions must be just right.
The outside of the glass must be exposed to cold air while the temperature inside of the glass is not as cold, but more humid. Water vapour deposits on the glass but the presence of dust or salt particles, and even residue from windshield washer fluid creates variations in the surface of the glass.
Both the shape and size of these particles affect how ice crystals form and branch out. This results in beautiful patterns like Brenda caught on her windshield and perhaps you have witnessed on your windows.
Fern frost isn’t as common as the usual coating we’re often stuck scraping off in the morning, but when it forms, it creates something truly amazing.