Taw River tin blowing mill, 840m south of Tawcroft

Reasons for Designation

Dartmoor is the largest expanse of open moorland in southern Britain and, because of exceptional conditions of preservation, it is also one of the most complete examples of an upland relict landscape in the whole country. The great wealth and diversity of archaeological remains provide direct evidence for human exploitation of the Moor from the early prehistoric period onwards. The well-preserved and often visible relationship between settlement sites, major land boundaries, trackways, ceremonial and funerary monuments as well as later industrial remains, gives significant insights into successive changes in the pattern of land use through time. Blowing mills (also known as blowing houses) survive as rectangular drystone buildings served by one or more leats and 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 square or rectangular stone built base of the furnace itself. During the medieval and early post-medieval period, black tin (cassiterite) extracted from streamworks and mines was taken to blowing mills to be smelted. At the blowing mill the cassiterite may have been washed a final time before being put into the furnace together with charcoal. To smelt tin the temperature within the furnace had to reach 1150 degrees 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. 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. All examples with a clearly identifiable surviving structure are therefore considered to be of national importance.

The Taw River blowing mill survives very well and is one of only seven examples known to contain a furnace. Important information concerning tin smelting technology survives within and around this building.

Details

The monument includes a tin blowing mill situated at the foot of a steep scarp adjacent to the River Taw. The mill building is of drystone construction with the wall standing up to 1.4m high. The interior of the mill measures 9.5m by up to 4.7m and access to it was through a clearly defined doorway in the north western corner. Within the eastern part of the mill, two edge set stones represent the site of the furnace, in which the black tin (cassiterite) was smelted. A recess in the eastern wall denotes the position of the wheelpit in which a wheel powered by water from the nearby leat operated the furnace bellows. The leat can be traced to a small reservoir measuring 12.8m long by 5.5m wide and up to 0.3m deep situated on top of the scarp immediately south of the mill. The water from the wheelpit was carried to the river in a tailrace which survives as a clearly defined channel denoted on both sides by substantial banks. To the west of the tailrace a level area represents the site of a dressing floor. At the northern end of the dressing floor is a horseshoe shaped hollow which may represent the site of a buddle or similar piece of apparatus. In the area immediately east of the mill fragments of tin slag have been recovered in the past.

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.

Legacy

The contents of this record have been generated from a legacy data system.

Legacy System number:

28751

Legacy System:

RSM

Sources

Other
Greeves, T.A.P. and Robinson, R., Taw River Tin Blowing Mill SX 62059197, (1985)
Unpublished plan, Greeves, T.A.P. and Robinson, R., Taw River Tin Blowing Mill SX 62059197, (1985)

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