Reasons for Designation
Approximately 10,000 lead industry sites are estimated to survive in England,
spanning nearly three millennia of mining history from the later Bronze Age
(c.1000 BC) until the present day, though before the Roman period it is likely
to have been on a small scale. Two hundred and fifty one lead industry sites,
representing approximately 2.5% of the estimated national archaeological
resource for the industry, have been identified as being of national
importance. This selection of nationally important monuments, compiled and
assessed through a comprehensive survey of the lead industry, is designed to
represent the industry's chronological depth, technological breadth and
regional diversity.
Ore hearth smelt mills were introduced in the 16th century and continued to
develop until the late 19th century. They were the normal type of lead smelter
until the 18th century, when they were partially replaced by the reverberatory
smelt mill. The ore hearth itself consisted of a low open hearth, in which
lead ore was mixed with fuel (initially dried wood, later a mixture of peat
and coal). An air blast was supplied by bellows, normally operated by a
waterwheel; more sophisticated arrangements were used at some 19th century
sites. The slags from the ore hearth still contained some lead. This was
extracted by resmelting the slags at a higher temperature using charcoal or
(later) coke fuel, normally in a separate slag hearth. This was typically
within the ore hearth smelt mill, though separate slag mills are known.
Early sites were typically small and simple buildings with one or two hearths,
whereas late 18th and 19th century smelt mills were often large complexes
containing several ore and slag hearths, roasting furnaces for preparing the
ore, refining furnaces for extracting silver from the lead by a process known
as cupellation, and reducing furnaces for recovering lead from the residue or
litharge produced by cupellation, together with sometimes complex systems of
flues, condensers and chimneys for recovering lead from the fumes given off by
the various hearths and furnaces. The ore hearth smelt mill site will also
contain fuel stores and other ancillary buildings.
Ore hearth smelt mills have existed in and near all the lead mining fields of
England, though late 18th and 19th century examples were virtually confined to
the Pennines from Yorkshire northwards (and surviving evidence is strongly
concentrated in North Yorkshire). It is believed that several hundred examples
existed nationally. The sample identified as meriting protection includes: all
sites with surviving evidence of hearths; sites with intact slag tips of
importance for understanding the development of smelting technology; all 16th-
17th century sites with appreciable standing structural remains; 16th-17th
century sites with well preserved earthwork remains; and a more selective
sample of 18th and 19th century sites to include the best surviving evidence
for smelt mill structures, and flue/condenser/chimney systems.
Despite its ruined state, Cobscar smeltmill retains rare visible furnace
structures, and further intact stratigraphy of both furnace structures and
process residues will survive hidden below the debris. The smeltmill was
active for 130 years and was altered at least once during its lifetime.
Archaeological evidence for this and other modifications made to the site
during its working life are believed to survive, which together with a
collection of rare contemporary photographs, will contribute to the
understanding of the smeltmill's opperation. The site also includes an in situ
slag heap which will retain important technological information about the
efficiency of the mill's processes, and the development of smelting techniques
over time. The intact chimney is also a local landscape feature.
Details
The monument includes the standing, earthwork and buried remains of an ore
hearth lead smeltmill, fuel store, and associated buildings, with the remains
of a flue system leading to an intact chimney. It also includes a short length
of flue from Keld Heads Mill and deposits of slag to the south. It lies
within an area of open moorland within a wider lead and coal mining landscape.
The monument includes the ruined remains of a waterpowered smeltmill built in
1762 to smelt ore from Cobscar Rake (upon which it is situated) and Cranehow
Bottom Mine 0.8km to the north east. The smeltmill was divided into into three
bays with a waterwheel (of c.6m diameter) powering a single set of bellows in
the central bay, blowing two ore hearths to the south and a slag hearth in the
remaining bay to the north. The building is choked with rubble following the
part demolition by the army in the late 1940s, but walling typically survives
to 2m, with one section surviving to a maximum of 4m. Photographs of the
buildings, prior to the part demolition, provide evidence of the internal
features of these structures. The bases of the hearths, settings for bellows
and other remains are thought to survive beneath the rubble. Features
that can be identified above the rubble include some of the iron strappings
for the ore hearths and the arched opening through an internal wall for the
bellows. Adjoining the north side of the smeltmill are the ruins of the
roasting furnace building added in 1848. It includes part of the roasting
furnace itself, which now stands to c.0.75m, retaining dressed stonework and
iron tie bars. From the west wall of the smeltmill, two flues run uphill,
merging after a few metres, to be joined in turn by the 2.5km long flue built
in 1855 for Keld Heads Mill to the south east, of which a c.100m length is
included in the scheduling. The flues, which have lost most of their capping
stones, are typically c.2.5m wide, with occasional narrow openings on either
side for maintenance access. The merged flue terminates at a chimney of a
plain rubble stone construction, c.3.5m square and 9m tall, with a single drip
course immediately below the coping stones.
To the south of the mill there is a small slag heap which will retain
important technological information about the smelting on the site. Extending
to the east side of the roasting furnace building there are the footings and
rear wall of a set of fuel and other storage buildings. To the south of these
there is a small courtyard, footings of another store house and a pair of
bingsteads (storage bays used for holding the unsmelted lead ore).
The smeltmill ceased work around 1890, but remained largely intact with in
situ machinery until the 1940s.
MAP EXTRACT
The site of the monument is shown on the attached map extract.
