By 1800 the Cornish mining and quarrying industries were consuming some 4000 barrels of gunpowder per annum, all of which was manufactured outside Cornwall. The first gunpowder mill in the County was at Cosawes Wood, Ponsanooth, set up by Nicholls and Gill in 1809; although small, its evident commercial success was enough to encourage the powerful Fox family to set up their own gunpowder business at Kennall Vale in competition. Licences for gunpowder manufacture were granted in 1811. The company seems to have been very successful and soon expanded. In 1844 its capacity was more than doubled when a complete new works was built higher up the valley in Roches Wood. The Kennall Company had by this time taken over the Cosawes mills, and for some time ran them alongside its own works; by 1870 they were in use only for storage. Another addition to the factory in the 1850s was a saltpetre refinery south of the main site. At its peak c1875, the Kennall Gunpowder Company consisted of the original works in Kennall Wood, including the Manager’s house, Sulphur Mill, and workshops; the ‘new’ works in Roches Wood, higher up the valley but continuous with the original; the farm below the main works; the Saltpetre Refinery; the Magazines adjacent to the farm; and the Charcoal Mill in Ponsanooth Village. In addition, the Company also owned several cottages in the village.
Modification and elaboration of the factory to suit changing demand and new processes continued through the latter part of the nineteenth century, although by this time the demand for gunpowder was in steep decline, owing to the collapse of Cornish mining and the development of the new nitro-glycerine based high explosives such as dynamite and gelignite. The directors of the Kennall Company were all too aware of these changed circumstances, and in 1889 established a new company to manufacture high explosives at Hayle — the National Explosives Company. The Kennall powder mills, now operating at greatly reduced production levels, were sold in 1898 to the biggest explosives making group in Britain, Curtis’s and Harvey. The new owners appear to have used the works at Kennall for some time to manufacture specialised types of cartridge and fuse powder, until production ceased c1910. The site was leased by Cornwall Wildlife Trust in 1985 for development as a nature reserve.
Kennall Vale represents the best-preserved gunpowder works in south-west Britain.
The quality of survival of the site is excellent, the buildings having in the main been of sturdy construction and the site not subjected to other uses following its abandonment. The site is a scheduled monument and is managed by Cornwall Wildlife Trust.