Late in the fall of 2021, I was driving up into the hills of Ester (which is just south of Fairbanks).  As I ascended, what seemed like a little bit of fog very quickly became fog and frost so thick you couldn’t see in any direction.  I pulled over to marvel at the frost covered trees that looked like they had stepped out of the pages of C. S. Lewis’ Chronicles of Narnia. I rolled my window down to inhale the threads of cold and mist, which were laden with pine and crisp air. I immediately realized I needed to capture this in soap. 
Excerpted from www.weatherology.com:  The first known use of hoarfrost came during the medieval period in England during the 13th or 14th century. It is not known who first used the term to describe a layer of frost, but at some point the term entered the lexicon of the English language. Its root is taken from the old English adjective "hoary" which means, gray or white in appearance. This word was often used to describe a person of age who had white hair and a white beard. Knowing this, it now makes sense how one would look at a frost-covered tree in that age and call the frost covering it hoarfrost. 
Now that we know the origin of the word, let's look into the science of hoarfrost. Hoarfrost forms on clear and calm nights, when the air is not only cold but also moist. The moisture in the air is a gas known as water vapor. When the water vapor comes into contact with objects that are well below freezing, it freezes onto that object. This change of state from a gas to solid ice results in the accumulation of what we know as frost. When a particularly heavy layer of frost coats the objects, it is described as hoarfrost.