By PAUL HETZLER
After the thermometer’s been in the negative digits for days on end, the morning may come when our car, smart phone, water pipes, fingers and other essentials have frozen and refuse to work. It’s easy to get so “frosted” by winter’s hardships that we miss its artistry. Given the right conditions, though, winter frost can transform the world overnight with a breathtaking majesty that would melt any heart.
Naturally, we tend to associate frost with the “bookends” of winter when the seasons are changing. The frosted lawn in April or October is neither unusual nor very interesting, at least not without a hand lens to see better detail. But mid-winter frost, while not as common, can be truly extravagant.
The kind of frost that turns any landscape into a winter magic-land is called hoarfrost, “hoar” being Old English for grizzled. Hoarfrost occurs in supersaturated air conditions when the relative humidity is more than 100%. This may sound like an impossibility, but in fact it’s common, at least for short periods of time.
In a humid air mass, as the temperature falls, relative humidity increases, eventually exceeding 100%. Supersaturated water vapor is an unstable condition, and nature is keen to restore balance by shedding moisture. On a cool summer evening that would be in the form of dew, and on a frigid winter night it’s hoar frost.
Those fortunate enough to live near a fast-flowing stream or river that stays open in the winter are treated to hoarfrost fairly often, as the open water provides necessary water vapor. Bodies of open water create moist air on a local level, but weather fronts can spread moisture, and thus hoarfrost, over a wide area.
In great literature and children’s stories alike, the theme of redemptive transformation is both compelling and appealing. Cinderella’s Fairy Godmother changed a pumpkin into a stagecoach; mice into fine horses. She has nothing on hoarfrost, however, which I think must have learned its craft from the angels themselves.
As water vapor condenses onto cold surfaces, it applies layer upon crystalline layer of fragile, feathery, exquisite ice forms. Even the most ordinary and neglected objects—the weed patch, the tangle of rusty barbed wire—are redeemed by hoarfrost’s magic wand. But given a medium that’s more complex, more inherently eye-pleasing such as a tree branch, the effect is all the more inspiring. When that effect is multiplied along fencerows and riverbanks, illuminated by morning sun, one has the urge to kneel on the spot and put a hand to one’s heart.
You can “farm” ersatz hoarfrost by combining cold temperatures, water vapor and a substrate on which to collect ice crystals. The first is easy—we have plenty of cold these days. Water vapor, which can be from an uncovered stockpot of water hot off the wood stove, needs to be concentrated in an unheated garage, enclosed porch or outbuilding. By definition, every object is a substrate, but more intricate objects result in more elaborate crystal formations.
This experiment might have to wait if you first need that pot of boiling water to thaw out your car or those water pipes in the crawl space. While doing so, please keep in mind that “hoarfrost” is not an expletive.
Paul Hetzler is a forester and a horticulture and natural resources educator for Cornell Cooperative Extension of St. Lawrence County.