Reasons for Designation
Gunpowder was the only explosive available for military use and for blasting
in mines and quarries until the mid-19th century. Water-powered manufacturing
mills were established in England from the mid-16th century, although powder
had been prepared by hand for at least 200 years. The industry expanded until
the late 19th century when high explosives began to replace gunpowder. Its
manufacture declined dramatically after the First World War with British
production ceasing in 1976. The technology of gunpowder manufacture became
increasingly complex through time with the gradual mechanisation of what were
essentially hand-worked operations. Waterwheels were introduced in the 16th
century, and steam engines and water turbines from the 19th century. Pressing
and corning were also introduced between the 16th and 19th centuries to
improve the powders. Pressing improved the explosive power of the mill cake
and corning broke the pressing cake into different sizes and graded it with
respect to its fineness. Additional techniques were developed throughout the
17th, 18th and 19th centuries to improve the quality and consistency of the
finished product, and this in turn resulted in a variety of types of powders;
ranging from large coarse-grained blasting powders used in mines and quarries,
to fine varieties used, for example, in sporting guns.
Gunpowder manufacturing sites are a comparatively rare class of monument with
around 60 examples known nationally. Demand for gunpowder centred on the
London area (for military supply), other ports (for trade), and the main metal
mining areas. Most gunpowder production was, therefore, in Cumbria, the south
west, and the south east around the Thames estuary. The first water-powered
mills were established in south east England from the mid-16th century
onwards, and many of the major technological improvements were pioneered in
those mills. All sites of gunpowder production which retain significant
archaeological remains and technological information and survive well will
normally be identified as nationally important.
The gunpowder factory at Powder Mills survives well and contains a
complete range of buildings and other structures and features associated with
the industry. Many of the buildings remain essentially intact, with only the
roofs and machinery having been removed. The system of leats and trackways
provides useful additional information concerning the character of the
factory. The unique survival of the associated proving mortar emphasises the
quality of the surviving archaeology. Together with a comprehensive historical
background this represents a fine example of a gunpowder production site.
The prehistoric settlement and cairn associated with the Powder Mills are
of national importance in their own right and contain information relating to
the exploitation of the central part of Dartmoor during the Bronze Age.
Details
The monument, which falls into five areas, includes a gunpowder factory, a
partially enclosed stone hut circle settlement and a round cairn situated
adjacent to the Cherry Brook. The gunpowder factory, which is Listed Grade II,
comprises at least 18 buildings involved in the production, storage and
management of gunpowder. Many of these buildings contained machinery
which was powered by water which was carried to the site by three large leats
from the East Dart and Cherry Brook rivers. These are included in the
scheduling. A system of trackways link the buildings and the river was crossed
by way of clapper bridges.
The gunpowder factory established in 1844 by George Frean, was certainly
operational by 1846 and remained in use until 1897, when it closed as a result
of increasing competition from dynamite and a slump in local mining activity.
The production of gunpowder involved combining a mixture of saltpetre,
sulphur and charcoal and the buildings in which the different stages of the
process were carried out survive at Powder Mills. The process was inherently
dangerous and to reduce the chances of cataclysmic explosions, the buildings
were situated at a safe distance from each other and each had a flimsy roof
which would have allowed any explosion to be carried upwards. Several
explosions are known to have occurred at Powder Mills and fortunately these
precautions may have ensured that no workers were ever killed.
Amongst the buildings identified at Powder Mills are: grinding mills,
where the ingredients were crushed separately between horizontal rotating
millstones; blending mills, where the ingredients were mixed in rotating
barrels; incorporation mills, where the material from the blending mills was
mixed further into a single compound; a range of buildings where the gunpowder
was broken, pressed, corned, dried, dusted and glazed; and finally charge
magazines, where the gunpowder was stored. Further buildings on the site may
have been used as storage or office accommodation.
The quality of the finished gunpowder had to be tested and at Powder Mills
this appears to have been carried out using two very different techniques. At
SX 63777681 a proving mortar, which was used to test the strength of the
gunpowder, still sits on a restored carriage. Whilst at SX 62757750 a number
of large boulders have been split using a single charge, possibly the result
of of testing. To the south west of the gunpowder factory stands an isolated
rectangular building in which finished gunpowder was stored prior to
transportation.
Within the vicinity of the gunpowder works there are four quarries from
which material was derived during the construction of the buildings. Parts of
the valley bottom contain earthworks related to tin streamworking.
A partially enclosed stone hut circle settlement lies adjacent to the leat
carrying water from the East Dart and survives as a series of four enclosures
associated with at least 13 stone hut circles. The enclosure walls are of
rubble bank construction standing up to 0.4m high. The stone hut circles
survive as circular or oval walls surrounding an internal area varying between
4 and 50 square metres.
A round cairn lies immediately west of the settlement and survives as an
8.7m diameter mound standing up to 0.9m high. Large edge set stones on the
north western edge of the mound may suggest the presence of a kerb which
survives elsewhere as a buried feature. A pit in the centre of the mound
suggests partial early excavation or robbing.
Modern post and wire fences, a shed and piles of sand and other materials
associated with a consolidation programme are excluded from the scheduling,
although the ground beneath them is included.
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.
