Blowing Mill at Outer Down

Summary

An early post-medieval tin blowing mill, terraced into a west-facing slope within the valley of the South Teign River. It is situated in the gardens to the west of Outer Down, an early-C20 country house (Grade II).

Reasons for Designation

The blowing mill at Outer Down is scheduled for the following principal reasons:
* Archaeological interest: the site is an early post-medieval blowing mill which is of national importance for the understanding of tin smelting;
* Survival: the blowing mill has been identified as one of the best surviving blowing mills on Dartmoor;
* Potential: the site has not been excavated and will contain important archaeological and metallurgical information concerning the character and technology of early tin smelting.

History

From the medieval period until the early C19 black tin (cassiterite) extracted from streamworks and mines was taken to blowing mills (also known as blowing houses) to be smelted. At the blowing mill the cassiterite may have been washed a final time before being put in the furnace together with charcoal. To smelt tin the temperature within the furnace had to reach 1150°C. This was achieved by blowing air through the furnace using water-powered bellows. Once the tin had become molten, it flowed from the furnace into a float stone and was ladled into the mould stone, in which it cooled to form an ingot of white tin.

Blowing mills are typically rectangular drystone buildings served by one or more leats and internally are characterised by the presence of granite blocks with moulds cut into them – bevelled rectangular troughs known as mould stones – and on occasion by the survival of the square or rectangular stone-built base of the furnace itself.

The original number of blowing mills on Dartmoor is unknown but at least 26 are believed to survive, whilst a further 41 are known only from stray finds and documentary sources. This blowing mill at Outer Down is considered to be of early post-medieval date and is located 250 metres to the west of the hamlet of Thorn. It is depicted on the current Ordnance Survey map as well as the second edition OS map published in 1905.

In 1927, a measured survey of the blowing house was undertaken by R H Worth. In the late C20 an analysis of slag recovered from the vicinity of the mill revealed that it contained 13.5% tin. This high proportion of tin indicates poor smelting efficiency and would, therefore, suggest a relatively early date for the operation of this blowing mill.

Details

The blowing mill which is probably early post-medieval in date, survives as a roofless ruin. It is built of granite blocks and is rectangular in plan. The interior is divided into two rooms, the smaller of which contains a wheel pit against the southern wall.

The blowing mill is terraced into a west-facing slope within the valley of the South Teign River. It survives as a ruinous, rectangular building; the walls standing up to 1.7m high. The interior of the mill is divided into two rooms. The smaller, western, room measures 4.9m long by 3m wide and contains a wheel pit built against the southern wall. The eastern room measures 7.4 m long by 4.9m wide and is filled with rubble. The internal dividing wall has a 1m wide opening at its north end. Although there is no visible evidence for the furnace, the dividing wall is of a greater thickness (1.5m) than the external walls which may indicate that this is the position of the furnace. Buried archaeological deposits associated with the furnace may survive in the vicinity of this internal wall. A broken mould stone has been incorporated into the north wall of the structure. The scheduled area occupies a roughly rectangular area measuring approximately 15m by 6m.

The mortar stone and mould stone within the garden of Outer Down, that lie some distance from the scheduled monument, are not included in the scheduling.

Sources

Books and journals
Gerrard, S, The Early British Tin Industry, (2000), 129-139
Greeves, T A P, The Devon Tin Industry 1450 -1750, (1981)
Worth, R H, Transactions of the Devonshire Association in A Blowing House In The Parish Of Chagford, Vol. 59, (1927), 343-5

Other
English Heritage, The Tin Industry, Step 3 Site Assessments: Devon, 1995,
Outer Down Blowing House, AMIE Monument 443644,
Blowing Mill at Outer Down, Chagford. Devon Historic Environment Record 6170,
Clampitt Leat, AMIE Monument 906788,
Scheduling documentation: SM34517,
Report for MPP, Greeves, T.A.P., An assessment of Dartmoor tinworking, (1990)

End of official list entry

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