Waterlogged wood is one of the most frequently encountered materials on underwater archaeological sites, and knowledge of its state of preservation whilst still in situ determines whether it can be raised and subsequently conserved, or whether it is sufficiently strong to withstand being preserved in situ. As noted previously, anaerobic bacteria cause deterioration of archaeological materials in marine sediments and, in the case of wood, they utilise the sugars and complex carbohydrates present in the wood cell wall as a source of nutrition. As deterioration proceeds material is removed and subsequently replaced with water – it is this water which fills the “voids” and allows the material to retain its form. Thus although freshly excavated wood may appear well preserved from an archaeological perspective, i.e. surface details and form are retained, it can be poorly preserved from a conservation perspective and if allowed to dry in an uncontrolled manner it will suffer irreversible shrinkage and collapse.

Within SASMAP a prototype hand held tool for assessing the state of preservation of waterlogged archaeological wood both in situ on the seabed and in the laboratory will be developed. This prototype will be based on research and development work which has been on going by partners 1 (NM) and 4 (AKUT). The prototype will be based on the non-destructive determination of the density of the wood. The net effect of bacterial deterioration is that as cell wall material is removed and replaced with water the density of the wood decreases - the more degraded the wood the lower the density. Density is a good physical parameter to provide information about the condition of wood and the implications this has for subsequent conservation or suitability for preservation in situ.

The partners are aware of the other commercial instruments available to assess the strength/density properties and deterioration of wood by measuring drilling resistance. These instruments tend to be sensitive to wood species, depth of measurement and the direction of penetration relative to the growth rings of the wood. Therefore they do not provide consistent and absolute data about the wood examined, furthermore they cannot be used underwater (in situ). The concept for the instrument to be developed in SASMAP has proven to be suitable for both fresh (undegraded) and archaeological wood in the laboratory and has several advantages over existing technologies. The instrument does not suffer from the aforementioned limitations and can be developed for underwater use. The device is expected to have broader implications for the non-destructive testing of non-archaeological timbers used in the marine environment (pilings, harbour installations) or on land (research, forestry, construction industry).
The concept for the instrument to be developed in SASMAP is suitable for archaeological wood in the laboratory and it has several advantages over existing technologies as it is not influenced by the anisotropy, depth of measurement wood species. Furthermore, there is currently no device commercially available that can provide this information in situ (underwater) for marine archaeologists and conservators. The device could have broader implications for the non-destructive testing of non-archaeological timbers used in the marine environment (pilings, harbour installations) or on land (research, forestry, construction industry).

Tools and techniques to raise waterlogged organic archaeological artefacts (WP5).
Due to their fragility, organic archaeological materials from underwater sites can be challenging to excavate, support, raise and transport to conservation facilities. This is due to the inherent difficulties of working underwater (limited time and potentially harsh conditions) and in particular the crucial stage of lifting artefacts from the seabed to the surface where mechanical damage can easily occur. Submerged prehistoric sites in particular contain a wealth of the aforementioned organic materials and complex structures such as fish traps. To surmount this, artefacts are often raised on supporting materials or in sediment blocks (block lifting), whereby the artefact is excavated with surrounding sediment and subsequently excavated under controlled conditions on land in the laboratory. Methods of encapsulating and block lifting have been used in the past to address this, yet can be very time consuming underwater, with artefacts being left exposed to physical damage at crucial stages while consolidating materials are allowed to “set” underwater.

SASMAP will draw upon the extensive excavation experience of partner 7 (VM) and the pioneering research into stabilising and consolidating archaeological remains underwater of partner 10 (MBAC)
in order to develop best practice methods. This will involve the development of the use of polymer based consolidants which can both encapsulate and consolidate sediments, as well as freezing of sediments in order to enable the safe lifting and transport of waterlogged organic archaeological objects.