Reasons for Designation
Large scale iron and steel production developed in Britain during the early
18th century. The centre of the steel industry at this time was the Derwent
Valley in County Durham where the use of new technology enabled the production
of more and better steel by a process known as cementation. Cementation
involved adding carbon to malleable (wrought) iron within a cementation
furnace, in order to produce blister steel bars so called because of their
blistered surface texture. Iron bars were packed in charcoal dust and sealed
into stone chests within the furnace. The chests were then fired for ten days
and allowed to cool. The resultant steel bars could be forged into billets or
finished artefacts, or were melted in crucibles to produce cast steel. High
grade imported Swedish wrought iron was normally used as locally produced iron
was found to contain too many impurities. Cementation furnaces
characteristically have three main elements. At the base a hearth, which ran
the length of the building, fed flames and hot gases into a vaulted chamber
below a tall cone which acted as a chimney. In addition cementation furnaces
are accompanied by ancillary buildings such as offices, stores and smiths and
other features such as spoil tips and hollow ways.
The technique of forging was primarily used in order to convert cast iron into
malleable iron bars by a process known as finery/chafery. During the finery
process the iron was re-heated in an open charcoal fired hearth, blown
by water powered bellows. Large quantities of water were required and typical
mill water supply features are often found in association with forge
buildings. These include weirs, headraces, ponds, dams, wheel pits and
tailraces.
Drift mining can be recognized by the existence of a regular straight mine
entrance, dipping inwards at a uniform angle. Drift mining commenced during
the 18th century but most known examples date from the 20th century.
As well as being the earliest cementation steel furnace in the British Isles,
Derwentcote is also the only intact and complete example. It represents a
steel making technology which lasted for more than 300 years and was an
essential part of the Industrial Revolution. The associated finery forge
retains significant archaeological deposits and will add greatly to our
knowledge of the development of the Iron and Steel industry in England. The
continued industrial use of the site for coal mining into the middle of the
20th century will add to its overall significance as an industrial complex of
great longevity.
Details
The monument includes the remains of a steel cementation furnace and
associated buildings and tips, an iron finery forge and water related
earthworks and a drift coal mine and associated structures and tips. They are
situated on the south side of the River Derwent above its confluence with the
River Tyne. The cementation furnace at Derwentcote is the only one of an
original six furnaces known to have been situated in the Derwent Valley during
the 18th century. Documentary evidence has established that the furnace was
constructed around the year 1733 and remained in use until 1875 when in its
latter years there was a shift to crucible steel production. A forge,
originally accompanied by a corn mill was constructed in 1718-19 and
remained in use until the 1850s when at this date it began to forge steel and
later changed to crucible steel production until its closure in 1891. The coal
mine dates from the 20th century and is known to have been operational during
the 1930s.
The steel furnace complex, oriented north to south, is situated at the top of
a steep north east facing slope. A road visible as a slight hollow way at the
extreme south end of the monument gave access to it from the former main road
between Derwent and Shotley Bridge. The furnace is a stone built structure,
buttressed on all sides with a central chimney or cone, containing two flue
openings on the ground floor. It is adjoined by buildings to the north, south,
and south east which have been interpreted as stores. Internally, the furnace
consists of a rectangular working space 5.2m by 3.2m, topped by an arched
brick vault. Two sandstone chests are situated either side of a central flue,
below which lay the ash pit. Part excavation at the steel furnace in 1987 and
1988 revealed that it was constructed slightly earlier than the adjoining
stores although they were all part of an original plan. Deposits of iron and
steel slag within the southern building suggest that it had been used for
forging or smithing; a tree stump embedded in the floor may have been used as
an anvil and an adjacent pit may have been the base for a second anvil or
hammer. In the northern part of this building the base of a possible charcoal
grinding mill was uncovered. The central ash pit beneath the furnace itself
was excavated and shown to have stairs giving access at either end. Part
excavation outside the furnace revealed the presence of further structures;
the first, to the west of the northern end was interpreted as a timber lean
to, while two timber framed buildings were interpreted as sand stores. A
series of track ways with metalled surfaces, containing debris from the
furnace and forge, were uncovered north of the latter. It is thought that the
track way was constructed at an early stage in the history of the monument.
Finally, excavation outside the southern part of the furnace buildings
revealed the existence of deep deposits interpreted as rubble from the
clearance of an earlier building on this part of the site.
The foundations of a rectangular building 7.5m by 3.5m, situated 29m south of
the furnace are thought to represent the remains of an associated office.
Immediately to the north and east of the furnace an arc of flat topped tips
radiating outwards are visible as a series of scarps up to 4m high. Analysis
of their composition has shown that they consist of an assortment of slag as
well as building stone and slate. A prominent hollow way bounded by a steep
bank connects the furnace with the site of the forge buildings, which is
situated at the foot of the steep north facing slope upon which the
cementation furnace stands. Several other tracks, visible as hollow ways and
slight scarps, are visible at the foot of the scarp in this area connecting
the buildings with each other and Forge Lane, which lies outside of the area
of the scheduling to the east.
The forge complex which occupies the flood plain of the River Derwent was
powered by water, and several of the water related earthworks are visible in
this area. The weir which dammed the River Derwent some 250m west of the
monument is no longer visible but water was removed from the river via a brick
inlet sluice which survives in a tumbled state. A headrace, running from the
sluice to the forge, is visible as a prominent earthwork 200m long, 5.5m wide
and a maximum of 1.9m deep, flanked by slight earthen banks. At its western
end it has become partly infilled. The mill pond, which provided a head of
water to operate the forge, now drained and silted, survives as an elongated
marshy hollow 100m long by 25m wide and to a maximum depth of 1.5m. The mill
pond was dammed at its eastern end by a stone dam and although this has been
breached it survives as an earthwork 2m high. A tailrace carried water from
the mill pond to the forge buildings and traces of an artificial channel 1.3m
deep to the east of the mill pond are thought to be the remains of this
feature.
Maps dating from the 19th century show that the forge consisted of two
building complexes. The first, or north range is situated immediately north of
the mill pond. This range is visible as a series of scarps 0.3m high, a sub-
rectangular depression 0.2m to 0.3m deep and a sub-rectangular platform 0.4m
to 0.5m high, in addition to the footings of several stone and brick walls and
mounds of tumbled rubble. The southern range straddled the main outflow
channel from the mill pond. Its north eastern corner is visible as a series of
earthworks 0.3m high, and hollows 1.3m deep, while parts of its eastern and
southern walls stand to a height of 0.5m. A wall 2m high which is visible on
the outer face of the mill pond dam is thought to be the remains of a wheel
pit.
Immediately west of the forge buildings there is a line of associated, ruined
buildings terminating in the ruins of a row of three stone cottages with
adjacent out-buildings and gardens standing to a maximum height of 2m in
places. The cottages had been converted by 1856, from an earlier rectangular
building containing a large opening in its south wall and this earlier
building formed part of the industrial complex.
East of the forge complex are the remains of a drift coal mine known from
documentary sources to have originated during the 20th century. The remains
include a mine known as Forge Drift surrounded by associated buildings,
platforms and spoil heaps as well as a mineral railway track. At the extreme
western end there is a depression 1.5m deep with a stone retaining wall and an
external bank. This feature has been interpreted as a loading bay for wagons
taking on coal from the railway lines which are depicted on a map but are no
longer visible on the ground. A mound of coal mining waste 1.2m high, is
situated immediately east of the latter feature. The forge drift mine workings
are visible as a concrete platform and a concrete edged hole 0.7m deep. The
entrance to the mine has been obscured by a collapse of the natural slope
across it. Several other features survive to its east as sub-rectangular
depressions and low scarps; these are all associated with the mine workings
and represent building platforms and mounds of mining waste.
The core of the monument is in the care of the Secretary of State and the
cementation furnace is a Grade I Listed Building.
The custodians office and the surfaces of all paths associated with public
access to the monument, all fences and the metal handrail adjacent to the
furnace, are excluded from the scheduling, although the ground beneath these
features is included.
MAP EXTRACT
The site of the monument is shown on the attached map extract.
