Izzie, as ever your view of the world is stunning. I love the butterflies in your door.
Frost or hoarfrost, is ice formed by the condensation of atmospheric water vapor on a surface when the temperature of the surface is below 32°F (0°C). In the formation of frost, a gas (water vapor) is changed directly to a solid. Frost often appears as a light feathery deposit of ice, often of a curious and delicate pattern.
Hoarfrost"A deposit of interlocking ice crystals (hoar crystals) formed by direct deposition on objects, usually those of small diameter freely exposed to the air.
The deposition of hoarfrost is similar to the process by which dew is formed, except that the temperature of the befrosted object must be below freezing. It forms when air with a dewpoint below freezing is brought to saturation by cooling. In addition to its formation on freely exposed objects (air hoar),
Hoarfrost is more fluffy and feathery than rime, which in turn is lighter than glaze. Observationally, hoarfrost is designated light or heavy (frost) depending upon the amount and uniformity of deposition.
Frost forms in exactly the same manner as dew except that the individual droplets that condense in the air a fraction of an inch from a subfreezing object are themselves supercooled, that is, colder than 32°F (0°C). When the droplets touch the cold object, they freeze immediately into individual crystals. When additional droplets freeze as soon as the previous ones are frozen, and hence are still close to the melting point because all the heat of fusion has not been dissipated, amorphous frost or rime results.
At more rapid rates of condensation, the drops form a thin layer of liquid before freezing, and glaze or glazed frost (“window ice” on house windows, “clear ice” on aircraft) generally follows.
At slower deposition rates, such that each crystal cools well below the melting point before the next joins it, true crystalline or hoar frosts form. These include fernlike assemblages. Just like the ones you have.
Check out:
http://www.its.caltech.edu/~atomic/snowcrystals/frost/frost.htm
