science

Case Study: The Carpow log boat

In 2006 a Bronze Age log boat was recovered from the banks of the Tay at Carpow. Perth & Kinross Historic Trust formed a partnership with National Museums Scotland for the conservation of this remarkably preserved 9m+ long boat. Without appropriate treatment the waterlogged timber would shrink and deform. Treatment required understanding the material science of waterlogged wood, knowing the degree of degradation and water content of the oak, and having access to large scale specialist facilities and expertise.

The Carpow longboat during excavation ©RCAHMS

Dr Theo Skinner, who was responsible for the conservation, reviewed possible treatment methods before selecting impregnation by polyethylene glycol (PEG) followed by freeze drying. Scanning Electron Microscopy (SEM) was used to identify surface accretions. Sulphur was found as a potential problem, and samples were taken for further analysis by X-ray spectroscopy at the Swiss synchrotron facility.

In collaboration with The Mary Rose Trust a potential new method to prevent the future build up of damaging sulphuric acid using calcium phytate was devised. The depth profile of water content in the timber was measured and used to specify the necessary PEG treatment and impregnation times, a programme which ran for approximately 18 months. Each section of the log boat was then treated in the NMS large object freeze drier (developed as a national facility for conservation of marine and wetland material), monitoring progress by measurement of water loss. Conservation work will run to the end of 2011, the integration of scientific analysis and measurement continuing hand-in-hand with practical treatment throughout.

Return to Section 3.9 Conservation science

 

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Case Study: Grooved ware at Barnhouse, Orkney

Figure 20:  Map of the vicinity of Barnhouse showing locations of igneous dykes (Jones 2002, Fig. 6.15)

Figure A: Map of the vicinity of Barnhouse showing locations of igneous dykes (Jones 2002, Fig. 6.15)

Excavations of the houses belonging to the Late Neolithic settlement at Barnhouse close to the Stones of Stenness, Maeshowe and Ness on Mainland Orkney revealed much Grooved Ware pottery (Fig. B). Jones’ study (2002, 2005) of this pottery looked at correlations between size of vessel, its decoration, fabric, content and findspot, enabling a detailed view of the production and consumption of this pottery to be built up.

Figure 21: Grooved ware vessel SF 3720 from Barnhouse

Figure B: Grooved Ware vessel SF 3720 from Barnhouse

There were five main fabric types, one shell-tempered, two rock-tempered which contained fragments of igneous rocks from different dyke outcrops in the vicinity of the settlement and common sedimentary rocks (sandstone, siltstone) and two untempered. The catchment area that the potters visited for these raw materials was evidently quite wide (Fig. A). In any case the source of clay or the way the clay was treated seems to have been matter of deliberate personal choice on the part of each potter or potters in each house. Each potter or house may have had its own ‘recipe(s)’. Furthermore, rock-tempered pots were found at the settlement’s periphery, while shell-tempered vessels were more common closer to the central area where the communal firing presumably took place. ORA has established a range of foodstuffs in the pots – milk, beef, barley, fruit (apples?) and multiple contents – this range being wider than that encountered in Grooved Ware elsewhere in Orkney which appears to be more commonly restricted to porcine and ruminant fats (Mukherjee, Gibson and Evershed 2008).

Figure 22: Photomicrographs of thin sections of Grooved ware at Barnhouse: 552  siltstone and camptonite   3507 granite and X; 1316 sandstone and siltstone

Photomicrographs of thin sections of Grooved Ware at Barnhouse: 552 siltstone and camptonite 3507 granite and X; 1316 sandstone and siltstone

Return to Section 3.4 Ceramics

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