Waterlogged archaeological wood

Jensen, P. and D. J. Gregory (2006), Selected physical parameters to characterize the state of preservation of waterlogged archaeological wood A practical guide for their determination, /. Archaeol. Sci. 33, 551-559. 

In the following discussion a number of conservation methods commonly used to treat archaeological artifacts are examined for their eflFects on subsequent technical examination. The preservation of archaeological textiles, waterlogged wood, archaeological bone and ivory, cuneiform tablets, and marine iron are among the problems considered. 

Recent studies into the condition of waterlogged archaeological wood from a range of sources, indicate that attack by tunnelling bacteria and soft rot fungi is more concentrated in the outer layers and erosion bacteria predominate deeper into the wood, suggesting the latter are much less oxygen dependent. 

The fundamental problem encountered if waterlogged archaeological wood is allowed to dry in an uncontrolled manner, is that it may shrink, collapse, distort, split and even in severe cases, completely disintegrate. The situation becomes a particular problem if the recently recovered wood is stored under conditions that do not prevent further deterioration. In an ideal world, it is... 

Research at the Mary Rose Trust has shown that gamma irradiation is a superior alternative to low temperature and biocide treatments of polyethylene-wrapped timbers and has been adopted by the Trust since 1998. Screening a range of bacteria and fungi isolated from waterlogged archaeological wood revealed that a dose of 15 KGy is required for the inactivation of most organisms (see Table 2). 

The feasibility of reburial as a storage method for waterlogged archaeological wood has been fairly well used. The near neutral pH, low Eh and absence of dissolved oxygen fulfil the requirements assumed by conservators for the... 

Conservation in the context of waterlogged archaeological wood must remove mineral inclusions and stabilise the size and shape of the object. In addition, the conservation treatment should be reversible, and give long-term stability. All treatments of waterlogged archaeological wood should adhere... 

As an alternative to PEG treatment of waterlogged wood, attempts have been made to use a radiation curing method involving a range of monomers and resins. The aim of such treatments is to reduce treatment times and achieve a more stable artefact. Styrene, vinyl acetate, acrylonitrile, acrylates and methacrylates are the most studied monomers in the treatment of waterlogged archaeological wood. The most widely used of these monomers is the water-soluble vinylpyrrolidone and methacrylamide and the non-water soluble chemicals such as n-butyl methacrylate monomer or unsaturated polyester resin. 

With the active conservation of waterlogged archaeological wood, the major problem is not that we do not have adequate treatment methods available, it is in recognising the serious limitations of these methods. However, those methods involving PEG offer the greatest flexibility and variability. 

Surely a few thought about the material, the wood, now archaeological wood about the physical and chemical state of the wood and the task of conserving this waterlogged wood about how the unique burial environment, through some fluke, allowed this wood to evade the natural cycle of deterioration for 333 years and about the secrets hidden in the wood, such as information about its age and the environment in which it lived, secrets revealed in its unique growth patterns. 

Most archaeological buried waterlogged wood is in the early process of diagenesis. Diagenesis is the natural process in which sedimentary materials are slowly compacted and eventually will form rock. In this natural process of change, 2000 or even 25,000 years is a short period. 

Conservation ethics have changed. A present concern is the use of the object for research. Most analytical methods are destructive. Any intrusive treatment, even as simple as using an algicide in storage water for waterlogged wood, can alter the research potential of the object (for example, distort the C date). And what about yet-to-be-devised analyses Many treatments alter the aesthetics of the object, and many treatments are not reversible. Conservators with their code of ethics may seem to have put unusually unrealistic constraints on methods of stabilizing archaeological wood, but this is not necessarily the case. 

Structure and Degradation Process for Waterlogged Archaeological Wood... 

ATERLOGGED ARCHAEOLOGICAL WOOD refers to wood that has been excavated yy archaeologists—regardless of size, species, age, or state of preservation—and is more or less completely filled with water. It is understood implicitly that the wood has been waterlogged for a considerable time, from decades to millions of years. Even very old wooden artifacts are often marvelously well preserved when excavated from below the water table, but they are very unstable once exposed to the ambient climate. They shrink, warp, and crumble in a frightening way, destroying the joy that only hours or days before lit the faces of the excavators. 

Figure 1. Cross sections of waterlogged archaeological woods showing zones of slight and heavy degradation, and the composition of the main wood constituents. Squares indicate where samples were taken for microscopy.

Freshly cut cross sections of waterlogged archaeological wood display some sort of zonation in most cases. Two or more zones can be distinguished by differences in color or hardness (checked by pricking with a pin). Where there are no different zones visible, either the wood will be very soft throughout or it will be about as hard as fresh wood. In the latter case there will probably be a very thin zone of softer tissue around the hard wood, even if it is only 1-2 mm thick. 

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