Up until the industrial revolution charcoal was the only viable fuel that ws capable of producing enough heat to smelt iron, as a result of this huge amounts of woodland were coppiced to provide the wood to charcoal which was then used to fire the furnaces.  So what is charcoal?

In essence it is merely wood that has had almost all the moisture extracted from it without cumbusting the fibres of the wood - in this state when burnt all the energy produced is emitted as heat, hence its folklore title of "black gold".  Nowadays it is mostly associated with fueld for BBQs but can still be seen in numerous items where is filtration properties have proved particularly valuable such as filters for masks (the chemical suits word by the armed forces are impregnated with charcoal) as well as other industrial uses.  As a woodsman who follows the ethos of "nothing is wasted" material not suitable for making greenwood products is used to produce charcoal.