Why Fire is Cool - entry #3 - Ash Ash Baby

When sitting around a campfire I almost always find myself silently staring, mesmerized by the smoldering ashes.  Once I snap out of it, instead of re-joining the conversation with my campfire pals  I often start taking pictures of the ashes.  Though it doesn't live up to the awesomeness of the moment, here is one (notice backlit marshmallow in foreground):

Before we discover the amazing things humans have done with ash, let's figure out what the hell ash is and why red-hot ashes look so awesome.  Once you burn away all of the combustible molecules in wood, the only things left behind (around 1% of the original unburned weight) are the non-combustible nutrients the tree used in order to stay alive.  Ash contains nutrients like calcium (~30% of the ash), potassium (~10% of the ash), and sodium ions (~1% of the ash) along with other metal and non-metal ions (reference).  It is partly these metal ions that make red-hot ashes look so awesome.  As you heat up metal ions in a fire, their electrons will gain energy then lose energy, in a process that results in the emission of light.  Each metal emits light of a specific wavelength, and if you take any substance containing metal ions and put it in a flame you will see this light (this is known as a flame test).