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Terra Preta - BioChar Woodcolliers


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Woodcolliers - Makers of Charcoal


The kiln is loaded first with a cartwheel of thin wood, followed by layers of varying sizes with larger pieces round the central log peg which is then removed to leave a central flue. Charcoal from a previous burn is dropped into it, with a paper torch and more charcoal.

Reduction in bulk and moisture takes place as the fire gets going and high temperatures are reached. The logs settle into the kiln, allowing the lid to be placed and sealed with damp sand. When the kiln drum starts to change colour from rust red to black, it is partially closed down by placing sand around the base to reduce airflow until an even fire is burning. Finally, side chimneys are fixed to internal flue pipes at ground level; by moving these round the flow of air through the kiln can be controlled, ensuring an even burn.

After 24-36 hours all flues are closed and sealed and the kiln is left for a further 24 hours to cool down. Extracting, grading and bagging the black mass of charcoal is the really dusty and dirty part of the operation. It takes between six and eight tonnes of timber to produce one tonne of charcoal.

The Trust is now stocking locally produced charcoal from sustainable sources and supporting local producers while encouraging traditional skills.

Join Ian Baldwin of Sylvan Charcoal in the Elstead area of the Wye Valley demonstrates the art of making charcoal from local sustainable woodland sources using steel kilns. Supporting your local charcoal maker will provide you with top quality lumpwood charcoal

The kiln
The charcoal kiln. Made from steel, kilns last for many years. Despite having to contend with the extreme heat of over 20 years' burns, Ian's is still going strong.

Digging out air vents
With the kiln empty, the starting point is to dig out the eight air vents at the base of the kiln and clean them to ensure regulated air flow for the burn.

Cleaning a chimney
Once dug out, the base of a chimney is thoroughly cleaned to remove debris from the previous burn. There are four chimneys and four air intake pipes to clean.

Bedding in air vents
After cleaning, the air vents are replaced and bedded in to ensure an air-tight seal.
Laying finings base
The next step is to lay a base of fines in the centre of the empty kiln. These will help the burning cinders to take hold for the burn when they're added later.

Spoke of logs
Spokes of large logs (bearers) are raised up against the central cone of fines. These will ensure that the channels to and from the air vents remain open to maintain air flow evenly throughout the whole kiln.

Chiltern Charcoal

Preparations for charcoal burning were made with great care, the stack built up in layers and always on level ground. The single wheeled barrow known as a 'mare' would be used for carrying logs to the burning area, and the large pronged rake for uncovering the charcoal when burning was complete.

Over half the woods in the Chilterns are ancient and have remained wooded for at least the last 400 years. These woods also contain many historic features of earlier land use as reminders of the way our forebears used them.

Stumps with many vertical stems coming out of them are a sign of coppicing techniques that were used to produced timber suitable for firewood, charcoal, laths and hurdles. The Chilterns used to supply much fuelwood for London.

Ancient beech pollards are a feature of some wooded Chilterns commons.

the Chilterns, a heavily wooded Area of Outstanding Natural Beauty to the north west of London, have been found to contain iron waste from small scale smelting or iron working activities. Most of these finds are just lying on the woodland floor in amongst the leaf litter. Some are thought to date back to the Iron Age and Roman period. The reason they are in woods is that perhaps as much as 60 tonnes of wood was needed to smelt a tonne of iron ore. The wood had to be converted to charcoal first so that it would burn hot enough to produce bloomery iron.

So why was iron produced in the Chilterns? It was much easier to bring the iron ore to the wood for it to be worked than to carry bulky and friable charcoal to the iron. Clay for the furnaces was also readily available in the Chilterns. The iron slag discovered so far seems to date from the Iron Age and Romano-British periods, although it is probable that some is early medieval.

Some of the iron slag found in Pigotts Wood, north of High Wycombe, Bucks, for example, still has the baked red clay lining from the bloomery attached to it; while other pieces are heavy fragments of the once molten slag. Another site nearby is in the woods owned by the National Trust at Bradenham. Some of this slag seems to be associated with medieval pottery but other finds here may be Romano-British.

A site with iron slag found within an old enclosure in Common Wood near Penn, Bucks, has had the enclosure ditch excavated by the Chess Valley Archaeological Society. They found Roman pottery fragments in the fill of the ditch and a bronze age spear was found nearby. So this is likely to be an early site for iron working.

Recent information from the records of the county archaeologists of Bucks, Herts, Beds and Oxon on the known distribution of iron slag sites in the Chilterns indicates that there are 9 sites in Bulbourne/Ashridge area of Hertfordshire (of 12 sites known in the county), 35 sites in Bucks, mainly north and east of High Wycombe. These sites are often in woodlands and some are linked to enclosures in the Wye and Misbourne valleys. A few sites are known in Bedfordshire near Dunstable (a Roman town), but there are no known sites (yet) in the Oxfordshire Chilterns.


Charcoal Making in the Forest of Dean


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Last modified: 06/20/08