I've been thinking too much about ash lately. I hope it won't bore anyone, but I thought i'd share some of what I've found about the chemical composition of various types of ash. I hope you guys find some use for it--maybe in choosing charcoal types, or an appropriate ash for forge and smelter floors.. None of these numbers are hard and fast, varying from place to place and between each individual members of species. If the numbers don't add up to 100%, assume a loss on ignition.
All data is taken from Digitalfire Ceramic Materials Database(link: http://digitalfire.com/4sight/material