Details

The monument includes the factory storage complex for finished gunpowder made
by the Kennall Gunpowder Company at Kennall Vale near Ponsanooth in west
Cornwall. The storage complex includes a distribution yard containing four
19th century gunpowder magazines serving, but well separated from, the
manufacturing area of the Kennall Vale gunpowder works which operated from
1812 to about 1910 further along the valley to the south west and beyond the
area of this scheduling. The three large gunpowder magazines within this
scheduling are Listed Buildings Grade II.
The distribution yard is sub-triangular in plan, 106m long east-west by up to
55m wide, tapering to the east to give a narrow approach to the yard's gated
entrance which opens onto the road linking Ponsanooth with the gunpowder
works. A row of three large gunpowder magazines extends north west-south east
across the yard's wider western end; a fourth smaller magazine is sited to
their east where the yard narrows towards the entrance.
The eastern half of the yard is levelled into the natural slope and defined
to north and south by tall rubble walls diverging gradually from the entrance:
the southern wall largely revets the steeply rising ground behind. Those walls
were already present when the 1840 parish tithe map was compiled, at which
date the yard area was open to ground sloping down to the River Kennall to
the west. By 1879, maps show the yard fully enclosed, as it still survives,
with well-built walls along its west and north west sides defining the yard
from pasture and stabling beyond this scheduling where the works' horses were
maintained for haulage within the manufacturing area and for carriage of
gunpowder from the yard to customers and to the port facilities at Penryn.
The three large magazines across the west of the yard are essentially similar
in construction though with detailed differences which partly reflect their
differing dates in the development of the yard: only the central and north
west magazines, 10.2m apart, appear on the 1840 map. The south east magazine
had been added only 5.5m from the central magazine by 1879. The magazines are
rectangular, aligned north east-south west, and measure in the range 9.2m by
6.25m to 10.9m by 5.7m. The walls rise approximately 2.75m to eaves height,
with gable ends between 4.2m and 4.9m high. The walls are of mortared granite
rubble with dressed granite blocks for quoins and for the lintels and
thresholds of the single doorway in each end wall. The roofs have collared
trusses resting on the tops of the side walls and supporting the purlins,
rafters and laths. All three magazines have a roof covering of small slates
rising to angled ridge-tiles. The roof survives largely intact on the north
west and south east magazines but is collapsing on the central magazine.
Each magazine has a blast vent roughly central in each long side wall,
visible as a single vertical slot in the outer wall face, forking within the
wall thickness to emerge as two vertical slots on the inner face, some of
which have been blocked. The central and south east magazines also have a
short vertical slot in the upper gable at each end. The central magazine also
has looped fittings to secure a former lightning conductor on its west gable.
The magazines were provided with floor level drainage slots variously spaced
along the side walls: small and neatly squared in the north west magazine but
formed as more irregular breaks through the wall fabric in the other two. The
north west and south east magazines also have a small lamp recesses in the
inner wall faces, on each side of their north east doorways.
Although several timber lintels occur over the inner face of some doorways,
the original wooden door-frames and steel doors have not survived, but broken
metal studs and plugs do remain in the cement render to which the door-frames
were fixed. The original internal pine racking has also not survived but
rows of wooden plugs and metal studs occur on the side wall inner faces where
the racking was secured.
The fourth, much smaller, magazine is located well to the east of the row of
larger magazines and measures 5.2m long, north west-south east, by 3.9m wide,
with a similar wall fabric to the other magazines. Originally it rose 1.7m to
eaves height, and 2.85m to the top of the gables, but recent alterations have
raised the roof level by 0.45m with block walling which supports a modern
roof of corrugated iron sheeting. The magazine has a granite-lintelled doorway
off-centre in the north west end wall; a central doorway in the south east
wall has been blocked with mortared granite rubble but retains its timber
lintel trapped between the blocking and the gable walling. A small blast vent
occurs towards the centre of each side wall, forming an angled, but not
forked, vertical slot passing through the wall fabric. Ventilation bricks at
ground level are modern additions. A stone gutter runs along the base of the
south west and north west walls. This small magazine is one of the yard's
early structures, appearing on the 1840 tithe map, and formed a small powder
store called an expense magazine. It would have been the first structure
encountered by persons using the yard entrance and from its easily accessible
position and small size, it is considered that this magazine may have stored
gunpowder for the works' factory-gate sales, without requiring customers to
approach the larger magazines where bulk supplies were stored before carriage
and shipment to meet the works' major orders.
A number of features are excluded from the scheduling; these are modern
dumped and stored materials within the storage complex, the abandoned car, the
modern roof, hen house fittings, the door of the smallest magazine, and the
modern gates and their fittings. The ground beneath all these features is,
however, included.

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 storage complex at Kennall Vale survives well, forming one of
only three 19th century factory storage complexes for finished gunpowder known
to survive nationally. The individual magazines each retain a good range of
original and distinctive features while their spatial arrangement within the
distribution yard reflects their respective roles for large and small scale
powder storage, an arrangement governed by contemporary safety regulations and
remaining barely affected by later visual intrusions.
The importance of the complex is further increased by its direct functional
relationship with the manufacturing remains of the Kennall Vale gunpowder
works which are also considered to be of national importance and which are the
subject of a separate scheduling. The physical separation of this storage
complex from the manufacturing area of the gunpowder works again reflects the
safety concerns and regulations affecting this industry during the 19th
century.

Source: Historic England

Sources

Other
Final Rept & Site Assment, Cornwall 2, MPP/Chitty, G, Gunpowder Industry Recommendations for Protection (Step 4), (1996)
List entries: Kerrier Dist, Stithians Par, SW 73 NW, 1/110-1/112,
MPP/Gould, S, Gunpowder Industry Combined Steps 1-3 Report, (1993)
Smith, J R, The Kennall Gunpowder Company, Kennall Vale, Ponsanooth, 1986, Unpub rept, Cwall Trust Nature Consvn
Title: 1:10000 Ordnance Survey Map; SW 73 NE
Source Date: 1984
Author:
Publisher:
Surveyor:

Source: Historic England