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It is believed that a grid of thick, green baulks was placed across the top of the wall to provide a platform for coppiced wood – Chopwood - to be stacked (Raistrick & Jennings 1965:144). There are several references, in the Lead Accounts, held in the Bolton Abbey estate office, which refer to three and on another occasion four baulks being transported from Grass Wood to other woods on the Duke of Devonshire’s estate in 1745 and 1754. A further reference ‘for lyeing in 7 new baulks’ at the Marrick smelt mill (NYCRO. ZCC/MIC 1756).A controlled fire burned in the pit below, accessed through the entrance, to heat and to drive off all the moisture from the chopwood stacked above. Control of the fire, in the kiln, was evidently essential. The baulks and the chopwood could catch fire, as a kiln did on one occasion in the Duke of Devonshire’s woodland in 1752 (Bolton MSS, lead file, letters). Documentary evidence also suggests that the pit or hole was deep enough to hold water. It was suggested that a ‘client who wished to smelt some lead should wait until after the wet season before drying chopwood as the kiln pit was full of water’ (Bolton MSS, lead file, letter dated 1754). Whitecoal which came out of Grass Wood, on the Devonshire estates west of Grassington, was produced by woodcutters and carriers, who also built, repaired and operated the kilns (Bolton MSS).
[Fig.1] [Fig.2] [Fig.3]
There is little other specific information on how the kiln was constructed other than several entries in Devonshire Estate Papers: “making one killn hole”, “making 2 kiln holes” (Bolton MSS Lead). Also references in the Marrick Estate Papers: “making kiln hole, “making kiln door” and “mending kilhole walls” (NYCRO. ZCC/MIC 1756). At Kettlewell there is a reference to “kiln holes for drying chopwood” associated with the smelt mill in a lease book of 1669 (Ashcroft 1984: 86, 87). These documentary references help to explain the function of the kilns, the remains of which are found in woodland close to lead smelting sites. Their purpose was for drying wood to produce whitecoal.
Numerous examples of chopwood kilns are found in upper Wharfedale in Yorkshire, many on the Devonshire estates, and are associatedd with the smelting of lead from Grassington Moor and other mines in the area. Similar kilns are found in Cumbria and Derbyshire [Fig.4]
Leads have been followed up from many sources, including Dr. Arthur Raistrick’s archives now in the University of Bradford and the Ironbridge Institute taking the author into several areas of woodland in upper Wharfedale, Swaledale, Derbyshire and Cumbria.[Fig.5] Confusion has been caused on many occasions in Wharfedale by the symbols used by Raistrick on his annotated maps of Grass Wood, Chapel House Wood and Todd’s Wood. Raistrick’s symbols for kilns range from: a capital ‘E’ within a triangle, ‘elling hearth’ or just plain ‘EH’. Consequentially there is potential for confusing chopwood kilns with those used to produce potash as they are very similar in construction. [Fig.6]
The major difference between chopwood and potash kilns is the working technique. In particular the entrance/air flue construction, although potash kilns tend to be much taller, perhaps 2m in height from base to top. Mr. M. Davies-Shiel suggests in his articles of 1972 & 1974 that potash kilns had a continuous wall surrounding the 2m high stone-lined bowl shaped structure (Davies-Shiel 1974: 34).
The width of the structure was 1m wide and integrated into it was a wind tunnel and air box which provided the working parts of the kiln. In addition to bracken, vegetation and brushwood was piled into the pit where a fire was lit. Air would have been sucked in through the wind tunnel and into the pit via the air box which was situated in the internal wall of the kiln at base level (Davies-Shiel 1972: 97). [Fig.7] [Fig.8] The fire was controlled by ash burners who poked and stirred the foliage/ash, from the wall at the top of the kiln, with long poles. If this structure was used for drying wood it would have been extremely difficult to control the fire, to ensure even burning, through such the restricted entry of the air box to prevent the platform and chopwood from catching fire and impossible to control the fire from above the platform. It is possible that chopwood kilns were dual purpose and the ashes from the pit were used to make domestic soap. [Fig.9]
This evidence is seen in the excellent example of a potash kiln recently identified in Bilsdale, on the North Yorkshire Moors (Harrison 2000: 20). At this stage of the research no chopwood kilns have been found in the Yorkshire area in sufficiently good condition to allow a full reconstruction of the working technique. However, a structure has recently been identified by the author in Hare Wood, Calstock, [Fig.10] east Cornwall close to the River Tamar. Its structure, proximity to the lead-silver mine at Buttspill (Stuart, 1991: 50) and an ancient smelter suggests that this is a chopwood kiln. This kiln shows several similar characteristics to the Yorkshire kilns and is in excellent condition due to many years of overgrown woodland foliage. The field evidence, the earthworks, for both types of kiln can be found in similar woodland environments or in areas of former woodland.
In the woodland of Froggatt Wood, Derbyshire (OL 24 NGR 247771) a different design of wood-drying kiln is found on the east side of a wheel-pit and smelt mill. Its design is very different to those found in Yorkshire. Although the general plan, built into banking and stone-walling enclosing a lined-bowl, is the same the rest of the design is completely different. [Fig.11] A central stone-wall emerges from the rear of the kiln forming two cells. This internal wall, the same height as the 1m surrounding stone wall, is 1m in length and terminates 0.05m from the kiln entrance providing an access to both cells of the kiln. Two stone baulks, which are built into the internal fabric of the kiln wall, span the gap to rest on the central wall. [Fig.12] Four more stone baulks were found close to the kiln. No information has been found to date to help the author fully understand the operational technique of this kiln. Other kilns known to exist in Derbyshire: ‘Q-Holes and white coal kilns’ have yet to be researched.
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