>Similar to hoar frost, these tiny crystals form when moisture is introduced to the glass surface and mingled with the smallest of imperfections on the glass surface.
When the outside temperature reaches a cold enough stage and especially if you add in any wind.. you can create these wonderful looking road maps of ice crystals. This was done by wiping a wet cloth on the inside of my living room window and allowing Mother Nature to do the rest, over a period of approx. 1 hour.
Today was just cold enough as it was well below zero and there is a prevailing wind, perfect conditions for creating road maps of this type, allowing some great photo opps.