CHARCOAL

The burning question

The production of charcoal is probably as old as the working of metal. When plain wood is burned there is a large quantity of water driven off, plus assorted chemicals, and this limits the temperature that can be achieved. The process of turning wood into charcoal is done by burning the wood in a low oxygen atmosphere, This rids the wood of the water and chemicals, and leaves behind the carbon skeleton that is recognised as 'charcoal'. When the charcoal is then burned with a good supply of oxygen, a much higher fire temperature can be maintained and with the careful use of the air supply, a high carbon atmosphere can be achieved in the fire. These are the ideal conditions for metal smelting, casting and blacksmithing.

The first stage of a charcoal clamp is to make a hole down the centre. This is to allow the fire to be started in the heart of the clamp, and to help air movement in the clamp in the early stages of the firing.
The rest of the wood is stacked around the core until you have a clamp about 6 feet high and 12 feet across.
The clamp is then covered with damp hay or straw. This acts as a barrier to the air and prevents the earth covering from falling in.
The clamp is then covered with earth and/or turf. Only the hole in the centre is left open, with a few vents around the clamp at ground level to allow air in to the base.
The clamp is then lit by dropping shovelfuls of fire embers down the hole in the middle of the clamp.
The fire is allowed to take good hold in the clamp. Once there are flames coming out of the top, timber is dropped into the central hole filling it completely. The top of the clamp is then sealed with straw and turf. The rest is a waiting game. A large clamp can take several days to burn. A watch must be maintained to block up any holes appearing around the clamp as the wood collapses. The charcoal is ready when a change in the colour of the smoke is detected. As the fire drives out the water the smoke is grey/white. When the charcoal is ready the smoke changes to a blue haze. At this point all holes are blocked up and the clamp is starved of air, and left to go out and cool down. The clamp is then dismantled. The charcoal is spread out to cool down and you can spot the bits that are still alight. Plenty of water must be available to damp down the remains of the fire. All that remains is to sieve and bag the finished charcoal.