The wonder of creosote!

When we came home tonight from a movie, I stoked the fire in the wood stove and saw this amazing pattern formed by creosote on the inside of the glass door of the stove:

  

How and why did the creosote form these beautiful abstract patterns? 

The movie was The State of Marriage, a documentary in the Brattleboro Film Festival about how Vermont came to be the first state to legally allow same-sex civil unions in 2000, and then nine years later, in 2009, became the first state to legalize same-sex marriage by a vote of the legislature (not the action of a court, as was the case in Massachusetts). 

It was an inspiring film that made us proud to be Vermonters. 

Poster for The State of Marriage