Stabilisation of waterlogged archaeological wood: the application of structured-light 3D scanning and micro computed tomography for analysing dimensional changes

Abstract

Cultural heritage objects made of wood can be preserved under waterlogged conditions for many years, where decay is slowed down and the wood structure is more or less completely filled with water. Depending on the degree of degradation, finds may collapse and shrink when they are allowed to dry in an uncontrolled manner after excavation, leading to total loss of the object and its information. Conservation measures are taken to prevent damage of objects and dimensional stability is an important criterion. In this study, structured-light 3D scanning and micro-computed tomography were used to analyse the dimensional stability of wood after conservation, as well as its long-term stability. 83 samples from a reference collection established between 2008 and 2011 allowed this comparative study of the most common conservation methods at that time. The effects of conservation methods using alcohol-ether resin, melamine-formaldehyde (Kauramin 800®), lactitol/trehalose, saccharose, and silicone oil on dimensional stability were investigated. In addition, different polyethylene glycol (PEG) treatments with subsequent freeze-drying were also investigated: one-stage with PEG 2000, two-stage with PEG 400 and PEG 4000 and three-stage with PEG 400, PEG 1500 and PEG 4000. The data received from analyses of both volume and surface gave detailed information about the success of each conservation method. Attempts were made to quantify the damage patterns, specifically shrinkage, collapse, and cracks. While PEG and freeze-drying, alcohol-ether-resin, as well as the Kauramin 800® method gave the best results, analysis also highlighted the failures of each method.

A multi-technique and multiscale comparative study on the efficiency of conservation methods for the stabilisation of waterlogged archaeological pine

“… The Anti-Shrink Efficiency (ASE) is shown for both, the samples of this study and reference samples from literature 20 . These samples underwent various treatments, including alcohol-ether resin (AlEt), Kauramin 800® (K800), lactitol/trehalose (LaTr), PEG 2000 (PEG1), PEG 400 and PEG 4000 (PEG2), as well as PEG 400, PEG 1500, and PEG 4000 (PEG3) prior to freeze–drying, saccharose (Sac), and silicone oil (Sil).…”

“…It is important to note that the observed trends appear to differ from the shrinkage measurements obtained in previous experiments (cf. Table 2 ) 20 . The earlier measurements encompassed a broader range of samples (with n values ranging from 7 to 10) and included additional factors, such as the type of wood.…”

“…The degradation is observed from the exterior to the interior, elucidating the strong decay of the outer area and the well-preserved inner region. The gradient shift in morphology towards the core is similarly highlighted by the Maximum Water Content (MWC) and the Basic Density (BD) 20 – 24 . These specific properties were ascertained through the measurement of the underwater weight (w sub ) and the wet weight (w wet ) and calculated ( 1 ) 25 .…”

“…The ASE, which is a metric used to determine the effectiveness of a wood conservation method in preventing shrinkage 15 , 42 was determined by measuring the volume of wet samples before treatment and dry samples after treatment using a structured-light 3D scanner 20 , 43 . Therefore, the wet samples were captured before conservation and in dry condition after conservation with an ATOS III Rev.…”

“…Conservation methods with significant relevance comprise alcohol-ether resin, Kauramin 800® (melamine formaldehyde), lactitol/trehalose, freeze-drying of polyethylene glycol (PEG)-impregnated wood, saccharose and organosilicon compounds 12 , 17 , 18 . The Anti-Shrink Efficiency (ASE) measurements demonstrate a substantial variation in the ability of these methods to stabilise finds 18 – 20 . This study analyses the factors contributing to the varied efficiencies of conservation agents and addresses three critical questions: (1) Is the quantity of conservation agents integrated into the structure a paramount factor for achieving volume stabilization?…”