Details

The monument includes a 19th century gunpowder works surviving beside the
River Kennall at Kennall Vale, near Ponsanooth in west Cornwall. The monument
also includes features from 20th century quarrying in the south west of the
gunpowder works, and part of two leats extending southwest - northeast across
the scheduling.
The gunpowder works, operated by the Kennall Gunpowder Company, was licenced
in 1811-12 to manufacture explosives for mining and quarrying. The company
reached its peak of production in about 1875, supplying most west Cornish
mines then operating, and having an extensive trade further afield. However,
decline rapidly followed with the collapse of the Cornish mining industries
and the replacement of gunpowder with nitro-glycerine based high explosives.
By 1898, the bulk of the company's business was as agents for high explosives
made elsewhere. Production finally ceased at Kennall Vale in about 1910.
The earliest phase occupied the downstream half of this scheduling and was
mainly focussed north of the river. A map of 1840 shows the Manager's House
by the works' entrance on the north east. Processing sites were spaced along
the valley behind the Manager's House. Surviving on the north bank of the
river from the early phase are traces of the glazing mill and extensive
remains of six incorporating mills, where mixed ingredients were ground to a
uniform powder by limestone edge-runners powered by water wheel. The
incorporating mills, which are Listed Buildings Grade II, are arranged as
three pairs, one of which had been added to an original two pairs by 1824.
Each pair had an overshot water wheel in a central wheel pit; their lower
chamber housed the wheel gearing; the upper housed the edge-runners on a stone
bed. The upstream two pairs of these mills survive almost to full height,
though lacking water wheels and internal machinery, floors and board roofing.
The downstream pair retain their wheel pit but were otherwise slighted in 1844
when the present masonry bridge, a Listed Building Grade II, was built over
the river to give access to the work's extension. The slighted mills were
replaced by another pair which survive well on an adjacent site upstream.
Water fed the upstream mill pairs from a leat taken off the river at a weir;
their tail-races formed a leat to supply the downstream pairs and their
replacements. The leats still flow, supported by masonry-revetted embankments,
as is a track giving access along the rear of the mills. Higher up the valley
side is a change house with fireplaces, where workers changed into works
clothing. On a rock-cut ledge above the Manager's House is the stove house, a
Listed Building Grade II, where powder was dried over steam-heated flues; its
drying chamber adjoins the intact boiler house and chimney.
Other early buildings were replaced in the work's later phases or were removed
by modern garden landscaping. South of the river are remains of the early
corning house, where powder was reduced in size and graded; unusually its
water wheel occupied a rock-cut chamber under the mill floor; nearby is a
small store.
In 1843-4 the gunpowder works expanded upstream, adding a new works in Roches
Wood which more than doubled its capacity. This included another four pairs
of incorporating mills, spaced along the north side of the river. These are
similar to the earlier pairs, with slight modifications, and they survive
similarly intact: the upstream pair has remains of its water wheel, supplied
by F W Dingey of Truro Foundry, though gearing within the mill derives from
20th century reuse. An elaborate system of revetted leats, still flowing,
operated along two levels to supply these mills; an even higher leat powered a
glazing house surviving beside the work's south west boundary blast wall. Many
processing sites in the extended area survive south of the river. Near the
south west blast wall is another corning house with its wheel-pit below the
floor, and a small store close to the north. To its north east are walls of a
combined dusting house, where dust was removed from the powder, and magazine
for powder storage. Another dusting house and separate magazine survive higher
up the slope. Beyond these are traces of the breaking-down house where the
pressed-powder cake was fragmented with mallets; an edge-runner stone now lies
on its floor. Further north east, the early 20th century granite quarry
extends over 80m of the upper slope; its deep flooded cut and adjacent loading
bay destroyed some of the gunpowder works' later buildings, and quarry dumps
overlie others. Several quarry related structures are spaced along 80m of the
track on the valley's upper southern flank; of concrete block construction,
they include a blacksmith's shop, a toilet block, a building built over a
gunpowder works magazine, and an engine bed. Further north east along the
track is a packing house built in about 1879; this single-roomed building
survives to full height: until a fire in the 1990s it retained its roof and
internal racking. A small built toilet further along the track had been added
by 1906.
The 1843-4 expansion also occasioned modification and additions which still
survive, in the early core of the gunpowder works, including the masonry
bridge already noted. South east of the bridge, a blast wall enclosed an area
north of the river containing the reinforced base of the compressed
cartridge house which produced pellets for blasting; beside it is walling of a
pump house and to the west is another small built toilet.
Between this enclosed area and the Manager's House, late 19th century records
show various buildings. Still surviving are the cooperage and the west half
of the foreman's office and store. The northern stub of the works' formal
entrance wall with a (blocked) pedestrian doorway projects from the foreman's
office into the track from the Manager's House. A less elaborate doorway
pierces a wall on the other side of the river. Walls of a magazine survive by
the track up to the early stove house, covered to each side by massive blast
walls descending the slope. Further west is a mixing house where the raw
materials were first combined. Small magazines survive west of the change
house and south of the river opposite the pump house. Various lengths of
surviving blast wall were strategically placed to contain risks from the more
dangerous sites in the works and a complex infrastructure of tracks and leats
served the many processing sites. The leats survive extensively intact and
flowing to the north of the river; south of the river, they were mostly fed
by water transferred from the north by aqueducts whose cross-river launders
do not survive; this southern system is now dry but much is traceable except
where disturbed by later quarry activity. Besides the works' leats, two
others pre-date 1840 and flow across the area of the scheduling: one follows
the south of the valley, leaving the scheduling for Ponsanooth where it
served the gunpowder works' charcoal mill along with corn and paper mills. The
other is taken off near the Manager's House and flows underground before
emerging as an open leat beside a quarried scarp next to the Manager's House;
it then leaves the area of the scheduling to feed a reservoir for the works'
former saltpetre refinery and runs on to Ponsanooth where it powered tape
mills.
The small fenced enclosure and the fence itself at the eastern end of the
scheduling, which contains a dwelling and garage, is not included in the
scheduling. However, the entrance to the gunpowder works and the leat to the
north of the fenced enclosure are included.
A number of features are excluded from the scheduling. These are: all modern
fences, gates and fittings, all garden furniture, the greenhouse and swimming
pool together with their associated modern bases, surrounds and fittings, all
modern metalled or paved surfaces, all modern footbridges, the cooperage, the
roof and modern internal fittings of the western half of the foreman's office
and store, the modern building on the site of the eastern half of the
foreman's office and store, the modern sluice gates, and all modern signs,
notices and their posts; the ground beneath all these features is, however,
included.
The Manager's House in the north east corner of the scheduling is totally
excluded from the scheduling.

MAP EXTRACT
The site of the monument is shown on the attached map extract.

Source: Historic England

Reasons for Scheduling

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 works at Kennall Vale provide one of very few surviving
examples of a large 19th century gunpowder manufacturing complex to retain
its overall integrity of layout with an unusually complete range of reasonably
well-preserved features. The surviving remains at this gunpowder works
include a number of especially unusual and rare components, most notably the
exceptionally well-preserved sequence of early mid-19th century incorporating
mills, the early stove house, the corning mills with their underground wheel
pits, the 1844 glazing house, and the unusually complex and intact leat
system. The packing house is a unique survival amongst extant remains of
gunpowder works nationally. Within its regional context, this was one of the
earliest gunpowder works to be established in Cornwall, only two years after
the first such factory had started production in the county in 1809. The
physical remains of the Kennall Vale gunpowder works are complemented by a
wealth of historical sources documenting the development of the company that
operated them. These sources show clearly the close integration of the works'
fortunes with the regional economy and with technological advances in
explosives.

Source: Historic England

Sources

Other
Cornwall Wildlife Trust, Management Brief: Kennall Vale, 1996,
Cornwall Wildlife Trust, Management Brief: Kennall Vale, 1996,
Smith, J, Kennall Gunpowder Company. An Archaeological & Historical Study, 1986, Unpub Rpt Cwall Trust Nature Consvtn
Smith, J, Kennall Gunpowder Company. An Archaeological & Historical Study, 1986, Unpubl Rpt Cwall Trust Nature Consvtn

Source: Historic England