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.
The Froggatt Wood smelt mill is one of the very few 16th-17th century smelt
mills in England to retain any standing structures. The water channel and
wood-drying kiln are unique within the lead industry, and the survival of an
undisturbed complex of this date, with a wide range of features, is very rare.
It has enhanced amenity value due to its location on National Trust land
within a National Park.
Details
The monument lies in woodland on the eastern side of the Derwent valley. It
includes a lead smelt mill and associated structures, contained within two
contemporary enclosures.
The water supply to the smelt mill is provided by a pond and dam on the east
side of the site, from which a channel of shaped stone blocks leads to the
mill. The smelt mill itself survives as a ruined building, orientated east-
west, within which a wheelpit is visible at the east end. The interior of the
building is full of rubble. To the west, tips of slag extend down the
hillslope, and a broken stone mould (for pouring pigs of lead) lies nearby. An
unusually complex stone wood-drying kiln lies to the south east of the
smelt mill, which was used to dry wood for use in the ore hearth of the mill.
The structures are contained within two conjoined enclosures, defined by
ruined drystone walls; a third enclosure to the north contains no visible
internal features and is not included in from the scheduling.
The character of the remains indicates a 16th-17th century date.
MAP EXTRACT
The site of the monument is shown on the attached map extract.
It includes a 2 metre boundary around the archaeological features,
considered to be essential for the monument's support and preservation.
