Abstract
Low-intensity drying is widely believed to protect waterlogged archeological wood against the adverse effects of dimensional alteration and cracking. However, slow drying generates substantial costs for the conservation process. This study compares the effects on conservation of highly-degraded sapwood (SW) and slightly-degraded heartwood (HW) from waterlogged archeological Scots pine wood treated with polyethylene glycol either as a mixture of polyethylene glycol (PEG) 400/4000 or PEG 2000 solution and air-dried using different approaches. The reference air-drying approach, using gradually decreasing air relative humidity (RH), i.e., 96, 86, 75, 66, and finally 44% (multi-stage schedule), was compared to an alternative approach, using constant RH of 44% (single-stage schedule). The Fourier-transform infrared spectroscopy (FTIR) analysis confirmed the decomposition of hydrophilic chemical wood components and revealed differences in the degree of degradation of waterlogged SW and HW. The drying time of PEG-treated waterlogged wood air-dried using a one-stage schedule was shorter compared to the drying time using multi-stage drying. Multivariate analysis (ANOVA) revealed that the drying schedule used after impregnation of waterlogged wood with PEG can have a beneficial effect on wood hygroscopicity and dimensional stability. The drying schedule significantly affected the equilibrium moisture content (EMC) of SW and HW and reduced tangential (ST) shrinkage of SW. These results show the positive effect of the single-stage alternative drying approach on the dimensional stability of highly-degraded Scots pine SW impregnated with PEG 2000. In the case of slightly-degraded HW, the drying approach did not affect wood preservation. These results can be useful for the conservation of highly-degraded waterlogged Scots pine wood.
Highlights
Wood residues found in soil or water, of natural or anthropogenic origin, referred to as waterlogged wood, are a valuable source of information about historical material and human culture and its interaction with the environment, as well as about past environmental conditions
The Fourier-transform infrared spectroscopy (FTIR) spectra differed between SW and HW of waterlogged Scots pine (Figure 3)
In the case of slightly-degraded HW, the absorption of Results of FTIR analysis confirmed the decomposition of hydrophilic chemical components of SW and HW in waterlogged Scots pine wood
Summary
Wood residues found in soil or water, of natural or anthropogenic origin, referred to as waterlogged wood, are a valuable source of information about historical material and human culture and its interaction with the environment, as well as about past environmental conditions. Wooden elements may be well or poorly preserved, corresponding to a low and high degree of degradation of the wood tissue, respectively. It is common for waterlogged wood to have internal differentiation of the tissues, i.e., some of the tissues will have high and some will have low degree of degradation. Waterlogged archaeological wood is often at high risk of cracking immediately following excavation. The risk of cracking of excavated wood can be eliminated by means of conservation procedures. A high coefficient of anti-shrink efficiency (ASE) is a recognized measure of the effectiveness of conservation [5]
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