Mary Lewis, age 9, of Peterborough, Ont„ for her question:
What causes frost patterns on the windows?
Feathers and ferny fronds, foxes' tails and filmy foliage ‑ Jack Frost has been painting the window panes. The delicate artwork is done in white and pale shades of silver grey. If‑the sun shines bright from a clear blue sky, you may catch a sudden diamond sparkle from the frosted window panes. For a moment you see a vivid flash of rainbow colors. This gives you a clue to the kind of paint used in Jack Frost's artwork.
The paint, of course, is ice from frozen moisture. Most of it is smudged and blurred like a finger painting. These colors are dull white and pearly greys. But here and there a few glassy ice crystals have been woven into the leafy fairyland. One of these can trap a sunbeam like a glass prism, split its skein of rainbow colors apart and send them dancing back into the air.
The painting is done on the outside of the window pane so let's go outdoors to examine the details. Run your fingers over the artwork. The brush strokes are thick and thin, rough and smooth. The frost at the edge of the feathery fronds tends to b e thin and rough. If you have a magnifying glass, you may see that it is a thin layer of fine grains and tiny ice crystals.
The graceful ribs and veins of the foliage tend to be smooth and thicker. They are curved ridges of solid ice. The thin areas of ice crystals add patches of crisp white to the design and the solid ice of different thickness adds the shades of pearly grey. The fine crystals tell how the frost gathered on the window pane and the ferny picture tells how the frost thawed a little and froze again, perhaps time after time.
During the day, the earth gathers warmth from the sun, but much of this heat escapes during the night. The ground is coldest just before sunrise, often colder than the air above it. This air touches the grass and the low branches with warm fingers. It is chilled as it touches walls and cold, glassy window panes. Chances are, there is water vapor in the air. As the air chills, some of this invisible gas must be given up. It may become a morning fog or a host of pearly dew drops. But on a cold, frosty morning, it is more likely to become an icy finger painting.
On such a morning, the temperature is way below the freezing point of water. The surplus vapor in the air is turned, not into moisture, but straight into fine crystals of ice. This happens when the warmer air touches the frost‑cold window pane and the glass is covered with crystal gains of ibe. Then a little heat may seep out from inside the house or a warmer breath of air may whisper on the frosty glass. The ice crystals melt and slide around in watery streams. The frost returns and freezes the running moisture into a solid picture.