The origins of fire-making are lost in prehistoric times, even antedating our own species, for it can be traced back to Peking man. The most widely used fuel was wood, although in the regions of two of the earliest civilizations, Egypt and Mesopotamia, where wood was in relatively short supply, other materials were used, such as dried ass’s and cow’s dung and the roots of certain plants, including the papyrus plant. But for the more demanding processes, such as the firing of pottery or the smelting of metals, wood and charcoal had to be imported. Charcoal is a porous form of amorphous carbon, made by burning wood with a supply of air insufficient to secure complete combustion.
It is the almost perfect solid fuel, for it burns to give a high temperature with little ash and no smoke. It was used widely for domestic heating, being burned on shallow pans, but, much more important, it was the fuel par excellence for industrial furnaces from ancient times until the seventeenth century, when it began gradually to be replaced by coal. The environmental, social and economic effects of the charcoal burner’s trade were profound, for vast tracts of forest land were laid waste to satisfy the voracious appetite of industry for fuel.
The method of making charcoal hardly varied over the centuries. Logs, cut into 90cm (3ft) lengths, were carefully stacked around a central pole into a hemispherical heap, up to 9m (30ft) in diameter at its base. The heap was then covered with earth or, better, turf, the central pole was removed and burning charcoal introduced down the centre to set light to the mass. Combustion was controlled by closing or opening air-holes in the outer covering.
The charcoal for iron smelting was often made from oak or ash, while alderwood stripped of its bark was used for charcoal that was to be ground fine for gunpowder. From the early nineteenth century the firing was carried out on a hearth that sloped towards the centre so that liquid products, particularly pitch, could be drained off. Pine and fir were preferred where these products were important, as they were for making timber preservatives, above all for the shipping trade, which required pitch for timbers and ropes.
Another important product of the combustion of wood was the inorganic, alkaline constituent of the wood, required in large quantities by glass- and soap-makers (see pp. 195, 203). All in all, the demands on the forest resources were great and ever-increasing; a substitute would sooner or later have been essential, but a rival claimant for timber made matters worse. Throughout this period timber was the main construction material and the demands of shipping, particularly the strategic requirement of navies, hastened the arrival of coal on the scene.