Skip to main content

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.

Introduction

Wood can be preserved in waterlogged anoxic environments for thousands of years. There, only a few microorganisms such as bacteria and fungi that use wood as a nutrient are viable in an environment with a low oxygen level [1,2,3,4,5,6,7]. During burial, microorganisms have had time to degrade the wood by actually consuming the material from it so that physical weakening of the structure has occurred. Water swells the wooden structure and fills the pore spaces—the capillaries and the microcapillaries. As the cell wall suffers from material loss more water will fill up the internal voids. Though, the moisture content of decayed wood is raised. The maximum moisture content is related to the state of preservation of wood and is a universally used indicator [8,9,10].

Depending on its condition, waterlogged archaeological wood will change its dimensions in two stages upon drying, due to collapse and shrinkage [11]. Above the fibre saturation point, cell cavities or lumina will collapse meaning irregular distortion unforeseeable in extent and distribution. The cause of collapse is capillary tension exerting compressive forces on the cell wall. As a result, the considerably weakened cell walls inevitably collapse [8, 12, 13]. Because of its heterogeneous state of preservation, there will be stresses developed in the object. In particular, the decayed shelf will dry first while the core is still wet [14].

Below the fibre saturation point, the cell walls will shrink [8, 15, 16]. The wood will then contract to a minimum of the original dimensions. Shrinkage in the tangential direction is generally more severe than radial and longitudinal shrinkage. But volumetric shrinkage is directly proportional to the water content of archaeological wood [10, 14].

There are several criteria to assess the effectiveness of conservation methods [14, 16,17,18]. One of the main criteria is to prevent the wood from shrinkage and to stabilise the volume of the object. The stabilisation involves the preservation of the shape of the object, which contains information such as the manufacturing technique and the function of the object [19]. The dimensions of the actual but swollen waterlogged state should be preserved and intervention should be kept to a minimum [20].

To avoid shrinkage and collapse of waterlogged wood upon drying is the main challenge for the conservation of archaeological wet finds [21, 22]. The damaging effect of air-drying and the question of how to solve this problem has already been noted in the nineteenth century as being not an easy task [23, 24]. Since then, a variety of methods and conservation agents have been tested in conservation [16, 25,26,27,28,29,30,31,32,33]. The heterogeneous material, the different types of wood and especially the widely varying states of preservation make it difficult to assess the success of a conservation method, and studies to compare different conservation methods have been made since the beginning of wood conservation [8, 18].

To check the dimensional stabilisation of a method, the condition after the conservation is compared with the condition before conservation. In conservation science, several measurement methods have been applied to assess methods by comparing the dimensions before and after conservation: The extent of dimensional changes was evaluated on thin sections under the microscope [13] or on wooden samples with exact dimensions [16, 18, 19, 34,35,36,37,38,39,40,41,42]. The surfaces were also compared by drawing the outline of objects [43]. To assess the anisotropic character of archaeological wooden objects during drying, samples were cut in accordance with the specific alignments [17, 44] or stainless pins were introduced into the wood [15, 16, 34, 45,46,47,48,49,50,51]. In recent times, also optical 3D measurement methods are used in laboratory studies [45,46,47, 49, 50, 52] and on shipwrecks [53].

The aim of this study is to assess the dimensional stabilisation of a number of established and most commonly used conservation methods on larger sample series consisting of different wood species. The research in this study focuses on the volume changes after conservation using structured-light 3D scanning. In addition, the sample material studied allowed to investigate the volume stability of the conservation methods after 10 years.

Normally, the evaluation of the dimensional stability of conservation methods is limited to the outer surface of the wood. Micro-computed tomography (µCT) offers a non-destructive technology for the visualisation of the structures inside. Until now there are only a few cases that have also considered changes inside wood after conservation using tomographic methods [52, 54,55,56,57,58,59,60,61,62]. These investigations have shown that shrinkage of the wood can also result in cavities inside. In addition to cavities, cracks in the structure can also be detected [62]. However, it is the overall structure that provides information on whether an object has been stabilised. For this reason, the samples in this study were also examined by µCT after their conservation, which allowed internal defects such as cell collapse and cracks to be taken into account when evaluating the conservation result.

Materials and methods

Samples

The material under investigation is a reference collection held at the Römisch-Germanisches Zentralmuseum (RGZM), Leibniz Research Institute for Archaeology. In a research project that was performed from 2008 to 2011 the most established conservation methods were investigated where approximately 800 samples were conserved at different Institutions with their standard methods (Table 1, Fig. 1). A detailed overview of the conservation methods and the samples is given on the project homepage [45]. The methods employed were alcohol-ether-resin [18], melamine-formaldehyde (Kauramin 800®) [63], lactitol/trehalose [64], saccharose [26], silicone oil [65] and polyethylene glycol (PEG) with subsequent freeze-drying. PEG treatment followed either a one-stage process with PEG 2000 [66], two-stages with PEG 400 and PEG 4000 [67] or three-stages with PEG 400, PEG 1500 and PEG 4000 [45].

Table 1 Overview of conservation methods
Fig. 1
figure 1

Samples of the KUR collection at the RGZM

The samples were taken from archaeological objects that were collected from different sites. The objects were made of different types of wood and have different degrees of degradation, which were divided into the samples. The degree of degradation was determined by the maximum water content (Umax). The mass of the waterlogged wood was determined without vacuum impregnation with water before measuring. Umax is defined as the water present in the sample compared to the absolute dry wood substance [2, 10]:

$$Umax= \frac{mass\, wet\, wood-mass \,oven \,dried \,wood}{mass\, oven \,dried\, wood}\, [\%]$$
(1)

Values of Umax have been classified by de Jong [51]. The numbers correspond to the water content ranges of the samples: (1) Umax > 400%, (2) Umax 185–400%, and (3) Umax < 185%. The maximum water content was determined destructively for the control samples to be air-dried, and non-destructively for the samples to be conserved [45, 67]. The density of the cell wall substance is usually assumed to be 1.5 \(\frac{g}{{cm}^{3}}\) [10, 68]. The water content is proportional to the void volume in the wood and inversely proportional to the basic or conventional density (BD, standard ISO 13061) of the wood in question (amount of wood substance per volume, g/cm3) [2, 69, 70]:

$$BD=\frac{100}{\left(66.7+{U}_{max}\right)} \left[\frac{g}{{cm}^{3}}\right]$$
(2)

To get an impression of how much wood has been decayed, the residual basic density (RBD) was calculated, in percent, as the ratio between the measured density of the archaeological material and the average basic density for non-degraded wood of the same species [10, 69], as derived from the literature [14, 71]:

$$RBD=\frac{BD}{BD (fresh \,wood)}\bullet 100\left[\%\right]$$
(3)

The non-destructive determination of the condition of the wood does not always lead to reliable results, due to both mineral inclusions and inclusions of air in intact fibres with non-degraded pits and cell-walls. Therefore, the average value from all samples was taken (Appendix A).

This systematic collection of samples provides a unique chance to compare the structural differences of the conserved wood [43, 46]. Each test series of the collection includes samples derived from the same object (same wood species and finding place, similar state of preservation) that were conserved with the different treatments. Due to the different sizes of the objects, the number of samples varied. Therefore, not all test series contain all conservation methods. For the volume analyses in this study, the ten largest test series of the collection were selected in order to cover a high variety of methods and wood genera. Sample series of different wood species were investigated: three from oak (Oa1, Oa2 and Oa3), two from fir (Fi1 and Fi2) and one from alder (Al1), ash (As1), beech (Be1), pine (Pi1) and spruce (Sp1). 83 samples were analysed (Appendix A). Figure 2 gives an overview of the sampling and measurement methods of this research.

Fig. 2
figure 2

Graphical overview of the experimental procedure: sampling, conservation, measurements with structured-light 3D scanning and µCT

Structured-light 3D scanning

From 2008 onwards, the wet samples were captured before conservation and in dry condition after conservation using a structured-light 3D scanner. The capturing device was an ATOS III Rev. 01 scanner from GOM (a ZEISS company) with a field of view of 500 mm × 500 mm × 500 mm and a point distance of 0.25 mm. After data capture, all scans were processed in the ATOS Professional 2016 Software using same parameters by employing Python scripts to control the workflow and obtain a reduced 3D mesh with a closed surface. To analyse volume changes after 10 years the conserved samples were captured again in 2020. Since the same sensor was no longer available, a successor model was used. The ATOS III Rev.02 Triple Scan from GOM (a ZEISS company) with a field of view of 320 mm × 240 mm × 240 mm and a point distance of 0.10 mm was used. The processing of scans results in 3D meshes of the samples.

Micro-computed tomography

Analysis of the condition of the wood structure inside the samples about 10 years after their original conservation was carried out at Lucerne University of Applied Sciences and Arts with a µCT-system. The tomographic analysis was performed on the in-house laboratory XCT system (Diondo d2, Germany). An optimised setup and acquisition protocol for the µCT measurements was developed for conserved wood. The measurements were conducted by setting the X-ray source (XWT-225 TCHE+ from X-ray works, Garbsen, Germany) in high power mode and choosing an operation voltage of 120 kV and a filament current of 167 μA with a 1 mm aluminum filter. The wood samples were mounted in a sample holder and placed in the sample chamber. The sample was rotated 360° in continuous mode during the acquisition. The radiographical projections were recorded with a 4343 DX-I X-ray detector (Varex, Salt Lake City, USA), with a pixel size of 139 μm. The distance between the X-ray source and the sample was between 160 and 250 mm and the distance between the X-ray source and the detector was 860 mm, giving a magnification between 3.4 and 5.4 and a nominal voxel size between 27 and 44 μm. A total of 3000 projection images were acquired during the sample rotation of 360°. The resulting projections were converted into a 3D image stack of approx. 3000 × 3000 × 3000 voxels using the CERA reconstruction software based on the filtered back projection Feldkamp algorithm [72] from Siemens. The achieved resolution of the µCT measurements depends on the size of the samples [73]. Appendix A gives an overview of the samples, their size and the achieved resolution of the µCT measurements. Image cross-sections and 3D renderings of the wood were visualised in VGStudioMax3.4© software.

Surface and volume determination and calculation of the dimensional changes

To get information about the surface and the volume of the samples measured with µCT the data was analyzed with VGStudioMax3.4. To obtain values of the wood volume concerning inner cracks and collapse, surface determination of the very heterogeneous material was done manually for each sample with the different segmentation tools of the software. Afterwards the surface and volume values of the segmented µCT data and that of the structured-light 3D scanning were calculated with the same software.

The evaluation of the conservation methods was done by determining the dimensional stability on the basis of the volume data that was derived from the surface of the whole sample. The values of the individual wood anatomical directions (tangential, radial and longitudinal) can be taken from the database [45].

To evaluate the volume changes in the measurement, data from structured-light 3D scanning was used to calculate the shrinkage (S) from the volume of the samples before (Vwet) and after (Vdry) conservation [74,75,76,77]:

$$S=\frac{{V}_{wet}-{V}_{dry}}{{V}_{wet}} \times 100\, [\%]$$
(4)

The anti-shrink efficiency (ASE) was determined from the shrinkage of a non-conserved control sample (So) and the shrinkage of the conserved sample (Scon) [15, 16, 78]:

$$ASE=\frac{{S}_{0}-{S}_{con}}{{S}_{0}} \times 100\, [\%]$$
(5)

100% ASE means a very good conservation has been achieved, whereas an ASE of 0% indicates a result equal to that accomplished by air-drying. An ASE of 75% seems to be acceptable [15, 16]. By using ASE, a statistical evaluation and comparison of conservation results is possible.

To probe the volume stability of conserved archaeological wood over time and the dimensional stability of the wood volume with respect to the inner structure, the values of the whole samples from structured-light 3D scanning and µCT were used. Analogous to the shrinkage after conservation analysis (Eq. 4), the volume change of the samples after 10 years was calculated from the volume after conservation and the volume 10 years after conservation. Similarly, the volume change concerning the inner structures of the wood was calculated from the volume of the structured-light 3D scanning 10 years after conservation and the volume of the µCT-data after 10 years. Surface changes (AO) were calculated additionally from the values of structured-light 3D scanning and µCT after 10 years:

$${A}_{O} change=\frac{{{A}_{O\, \mu CT}}-{{A}_{O\, scan}}}{{{A}_{O\, scan}}} \times 100 [\%]$$
(6)

To get an impression of the size and shape of the cavities inside the samples the volumes and surface areas were determined by the difference between structured-light 3D scanning and µCT data. From these values the sphericity ѱ was calculated:

$$\uppsi = \frac{{\sqrt[3]{{36\pi V^{2} }}}}{{A_{O} }}$$
(7)

The sphericity ѱ relates the shape of a body based on its volume (V) and its surface (AO) to the smallest possible surface of a sphere of the same volume [79]. The value of the sphericity ѱ for a sphere is 1. The lower a value of sphericity ѱ is for a shape, the larger the surface area is compared to a sphere.

Results and discussion

Volume changes

Appendix B shows the values for the volumes of the structured-light 3D scans before and after conservation. The measurements show extensive shrinkage of the unconserved wood samples. In Fig. 3 the loss of volume after air-drying of the untreated wood shows a relationship with the condition of the wood which is calculated as the residual basic density in per cent (Eq. 3). There is a clear trend showing that the better the wood is preserved, the less volume change occurs during air-drying. Figure 3 also demonstrates less shrinkage of all conserved samples in comparison to the air-dried samples. There is a difference between the conservation methods concerning the samples with a higher degradation and a lower residual basic density. It is evident that the stabilisation of these samples treated with saccharose, lactitol/trehalose or silicone oil is not as sufficient as compared to the other treatments.

Fig. 3
figure 3

Loss of volume after air-drying untreated samples and conserved ones in relation to the condition of the wood (residual basic density in %)

This tendency is also confirmed by the calculation of the ASE (Eq. 5). Figure 4 shows the ASE of all sample series in relation to the preservation status. For a better overview, the average value (x̅) of the residual basic density is given here for each sample series. In Fig. 4 it becomes even clearer that strongly degraded sample series are less stabilised by the conservation agents saccharose, lactitol/trehalose and silicone oil than by the other conservation agents. In addition, it also becomes obvious that the overall volume stabilisation decreases with a better state of preservation. The threshold here is a residual basic density of about 60%. This limit indicates that the preservation state 2 after de Jong [51, 80, 81] is particularly difficult to conserve due to two different states of preservation in one object [17]. The µCT data confirms that in these test series (Pi1, Fi1, Oa1 and Oa2) samples have highly degraded and low degraded areas. In contrast, the more degraded sample series show a consistent picture in the µCT data. The cross-sections of the samples As1-K800 and Pi1-AlEt show the difference between one homogeneous state of preservation (Fig. 5) and two states of preservation in one object (Fig. 6).

Fig. 4
figure 4

Volume stability (ASE) dependent on the average residual basic density x̅. The conservation method is given on the data point

Fig. 5
figure 5

µCT cross section of the ash sample conserved with Kauramin 800® (As1-K800) with one homogeneous state of preservation

Fig. 6
figure 6

µCT cross section of the pine sample conserved with alcohol-ether-resin (Pi1-AlEt) with high degraded area left and low degraded area right

Apart from the state of preservation, there are also considerable variances in the conservation methods in the individual test series with different wood species. All conservation methods improve stabilisation to some degree. Taking all the results into account and looking at the average of the volume changes for the different conservation methods, a general trend can be seen (Fig. 7). The best results are mostly achieved using PEG, the alcohol-ether method or Kauramin, although there are exceptions. The individual conservation methods with their deviations and special features will be discussed later in detail.

Fig. 7
figure 7

Average shrinkage of all selected samples after conservation, after 10 years and including the inner structures derived from µCT

Appendix C shows the values of the volume changes after 10 years. Here, it is particularly noticeable that almost all unconserved wood samples are not stable. With a few exceptions, the changes in the conserved samples are very slight and no clear trends can be identified for the individual conservation methods. All conservation methods thus seem to permanently stabilise the samples, as can be seen from the average values for volume change after 10 years (Fig. 7). In Appendix C, the internal structures are considered and the extent to which this changes the volume. Since no µCT data of the previous state is available, the values of the µCT data are compared with the values of the surface scans of the current state 10 years after conservation. Since the original condition of the interior of the samples is unknown, this is primarily a comparison of methods. It should be noted here that the µCT not only considers internal cavities, but also, in contrast to the surface scan, considers and more accurately depicts crevices and depressions (Fig. 8). Nevertheless, differences in the conservation methods become apparent when looking at the average value of the volume change inside all samples. The conservation methods with Kauramin 800®, saccharose, lactitol/trehalose and silicone oil seem to lead to a greater change in volume inside the samples than the other conservation methods (Fig. 7).

Fig. 8
figure 8

µCT cross sections of two examples (Oa3-K800 left and Oa3-Sac right) for the comparison of the surface detection with structured-light 3D scanner and µCT

Volume changes in relation to the surface

Another indicator for the stabilisation of a sample that can be obtained from surface scans and µCT are changes in surface values. Obviously, if only the outer surface is considered, it will also decrease with volume shrinkage. By comparing the surface data with the µCT data, a value for the surface inside the sample is obtained, which can provide information about cell collapse and cracks in the sample (Appendix D, Eq. 6).

If the surface area increases in the µCT data, we are dealing with cavities inside the sample. Again, it must be considered that due to the lack of the previous condition, it cannot be clearly proven whether the cavity was already inside the wood before the conservation. In some cases, there is also some uncertainty due to deeper cracks in the surface that were not detected by the structured-light 3D scanner (Fig. 8). When looking at the µCT data, however, cell collapse is definitely evident (Fig. 9). In addition, clear cracking can be seen in the samples conserved with PEG that were freeze-dried (Fig. 14) [46, 52].

Fig. 9
figure 9

µCT cross section of the alder sample treated with alcohol-ether-resin (Al1-AlEt) with cell collapse in the wood structure

The values for the enlargement of the surface and the shrinkage in percent, resulting from the comparison of surface scan and µCT, are listed in Appendix D. From the values, it is possible to see, to some extent, if collapse and cracks appear inside the wood samples. If neither the volume nor the surface have changed much, this means that the sample is also stable inside. In contrast, it can be assumed that a large surface increase combined with a large volume loss can only be explained by a significant collapse inside the sample. An example of this is the alder sample (Al1-LaTr, Fig. 10). A surface increase of 305% and a shrinkage of 16%. If only the volume has changed considerably and the surface does not change so significantly, it can be assumed that isolated, large cracks or fissures have occurred within the wood. This is the case with the oak sample (Oa2-K800), which is also shown in the cross-section of the sample (Fig. 13). In relation to the volume loss with 15%, the surface with 144% has changed far less compared to the alder sample (Al1-LaTr, Fig. 10). If, on the contrary, the surface has increased considerably with a smaller change in volume, this is a sign of many fine cracks within the wood, as has already been mentioned for the wood conserved with PEG and freeze-dried. An example of this is the ash sample (As1-PEG1), which has a relatively stable volume with a shrinkage of 1% but a large surface enlargement with a value of 218%. The fine cracks, leading to these values, can be seen in Fig. 14. Such obvious changes in the wood structure and the measured volume and surface values are discussed below individually for each conservation method studied.

Fig. 10
figure 10

µCT cross section of the alder sample treated with lactitol/trehalose (Al1-LaTr) with cell collapse in the wood structure

Another way to approximate the shape of these cavities inside the wood is to calculate the sphericity ѱ, which relates the shape of a body based on its volume and its surface to the smallest possible surface of a sphere of the same volume (Eq. 7) [79]. The lower this value for a shape, the larger the surface in relation to a sphere. The values determined in this way show a wide variation and are probably dependent on the conservation agent, the type of wood and the state of preservation. However, tendencies for the different conservation methods can be derived from the averaged values (Fig. 11). In contrast to the other methods, the values obtained from samples treated with PEG scatter far less. This could be an indication that a more uniform and reliable conservation result can be achieved here. Furthermore, the average values obtained from samples treated with PEG are noticeably low. The sphericity ѱ confirms the picture that fine cracks tend to form in these cases.

Fig. 11
figure 11

Sphericity ѱ (average values with standard deviation) of the cavities inside the samples determined for the different conservation agents from structured-light 3D scanning and µCT data

Dimensional stabilisation provided by the conservation methods

Alcohol-ether-resin

The samples conserved with the alcohol-ether-resin show very good volume stabilisation overall. With two exceptions, the values determined for the ASE of the scans before and directly after conservation are above 90% (Appendix B). The oak sample (Oa2-AlEt) also has a very good ASE value of 88%, while the pine sample (Pi1-AlEt) having the lowest value, with an ASE of 76%. This could be due to the preservation state 2 according to de Jong [51, 80, 81] with two different levels of degradation (Fig. 6). The scans after 10 years show consistently good values for volume stability. Considering the internal structures resulting from the µCT data, the method also shows good volume stabilisation (Appendix C, Fig. 7). Only the alder sample (Al1-AlEt) shows a poor value with more than 5% additional volume loss. If the surface change of the samples preserved with alcohol-ether-resin is added, the predominantly positive overall picture is reinforced (Appendix D). The low surface increase when considering the internal structures on the basis of the µCT, together with the simultaneous low volume loss, indicates that there was little collapse or crack formation in the interior of the specimens, which is also confirmed by the cross sections of the samples in µCT data. An exception is again the alder sample (Al1-AlEt), which shows a comparatively high value of 137% surface increase, which in connection with the volume loss indicates an increased cell collapse inside the sample. This is supported by the observation of the µCT data (Fig. 9). It should be noted here that in this series, poorer values are observed overall in comparison with all conservation methods, which may be explained by the fact that cavities were already present in the wood before conservation. This positive assessment is also confirmed in previous studies [18] especially for broadleaved woods [82].

Kauramin 800®

The samples conserved with Kauramin 800® also show mainly very good results. With two exceptions, the ASE directly after conservation shows values above 90% (Appendix B). Five of the ten samples even show an ASE of 99% to 101%. The samples with lower values are the pine sample (Pi1-K800) with an ASE of 87% and the oak sample (Oa1-K800) with an ASE of 88%. The pine sample (Pi1-K800) comes from the same sample series as the previously mentioned pine sample (Pi1-AlEt), which, with two different areas of degradation (de Jong: 2), also has the worst value of the alcohol-ether-resin. Volume stability is guaranteed for Kauramin 800® even after 10 years. A somewhat different picture of the method emerges when looking at the µCT data. While the positive results for most samples are confirmed by a small additional volume loss, a different picture emerges for the oak samples (Oa1-K800 and Oa2-K800) with two different states of preservation (de Jong: 2, Appendix C). The additional volume loss of 10% and 15%, respectively, is also significantly reflected in the overall results of the method (Fig. 7). It is striking that this volume loss is caused, in both cases, by large gaps that run along the two different maintenance states in the wood (Figs. 12 and 13). The low values of surface area increase in relation to volume loss confirm here that large fissures are involved (Appendix D). Overall, the samples preserved with Kauramin 800® show greater surface area increase than the samples preserved with alcohol-ether-resin, suggesting that cell collapse and cracking have increased in these. This may be due to the fact that it is too stiff and is not easy to deform. This has been criticised in the literature regarding previous methods using melamine resins [18]. It has also been described that Kauramin 800® stabilises highly degraded wood very well, while well-preserved wood is stabilised more poorly. This could be due to poorer penetration of the amino resin prepolymer, resulting in collapse and shrinkage of the well-preserved wood [17]. This becomes obvious in samples with two different states of preservation.

Fig. 12
figure 12

µCT cross section of the oak sample treated with Kauramin 800® (Oa1-K800) with a large crack in the wood structure

Fig. 13
figure 13

µCT cross section of the oak sample treated with Kauramin 800® (Oa2-K800) with large cracks in the wood structure

Fig. 14
figure 14

µCT cross section of the ash sample treated with PEG 2000 and freeze dried (As1-PEG1) with cracks in the wood structure

Lactitol/trehalose

The samples conserved with lactitol/trehalose were inferior to the previously mentioned methods. The ASE of the samples directly after conservation is between 76% and 92%, whereby only the beech sample (Be1-LaTr) with an ASE of 92% has a value above 90% (Appendix B). A change in volume after ten years is also not observed in the woods conserved with lactitol/trehalose. Looking at the internal structures based on the µCT of the samples preserved with lactitol/trehalose, this also confirms poor volume stabilisation (Appendix C, Fig. 7). In particular, the alder sample (Al1-LaTr) and the oak sample (Oa3-LaTr) have poor values with 16% and 14% additional volume loss, respectively. If one adds to the volume loss the strong surface change in these samples (Appendix D), this indicates that considerable collapse has occurred inside these samples. Figure 10 shows a cross-sectional image of the µCT, which illustrate the collapse of the wood structure.

Polyethylene glycol (PEG 2000) one-step and freeze-drying

The samples conserved with PEG 2000 and then freeze-dried show predominantly very good volume stabilisation (Appendix B). Except for two samples, the ASE values are above 90%. In six of the ten samples, the ASE is between 99% and 105%. The samples with the lowest values are the oak sample (Oa1-PEG1) with a value of 83% and the oak sample (Oa2-PEG1) with a value of 89%. The scans after 10 years also show consistently high values of volume stability for the samples conserved with PEG 2000. Similarly, the µCT data confirm good volume stabilisation inside the samples (Fig. 7). With just over 2% additional shrinkage inside the samples, the alder sample (Al1-PEG1) and one of the two fir samples (Fi2-PEG1) have the highest values (Appendix C). If the surface change is also considered, it is noticeable that these two samples also exhibit a large surface enlargement with values above 200%. With the exception of the first fir sample (Fi1-PEG1), such a surface increase is observed in all samples preserved with PEG 2000 and freeze-drying (Appendix D), which can be explained by the formation of cracks. Figure 14 shows these cracks, for example, in the ash sample (As1-PEG1). With the exception of the fir sample (Fi1-PEG1), these cracks occur in all samples conserved with PEG 2000. The first step in the freeze-drying process is the freezing of the impregnated wood. Freezing the aqueous solution in the wood leads to the expansion of its volume [83] leading to cracks. Specimens preserved with PEG exhibit low strength [18]. This fragility is further increased by the cracks that have formed as a result of the conservation.

Polyethylene glycol (PEG 400 and 4000) two-step and freeze-drying

The samples conserved in stages with PEG 400 and PEG 4000 and afterwards freeze-dried also show a predominantly favourable volume stabilisation (Appendix B). With the exception of the values of three samples, the calculated ASE is above 90%. The samples with the poorest values are the oak sample (Oa2-PEG2) with a value of 89%, the pine sample (Pi1-PEG2) with a value of 87%, and the second oak sample (Oa1-PEG2), which dropped sharply to 74%. The scans after 10 years show satisfactory volume stability, in line with the other conservation methods. Considering the results of the µCT, a similar picture appears as for the conservation with PEG 2000. The volume stabilisation inside the samples is good and with a value above 3%, the oak sample (Oa3-PEG2) has the highest additional shrinkage (Appendix C). An increase of the surface area with a good volume stabilisation inside the samples can also be observed, which in turn suggests the formation of cracks inside the samples (Appendix D). The cracks occur less strongly than with the other PEG methods. However, they are clearly visible in seven sample series. The fir samples (Fi1-PEG2, Fi2-PEG2) and the spruce sample (Sp1-PEG2) have no obvious cracks. In one case, in addition to cracks in the outer area, it can also be observed that the wood structure in the centre has collapsed (Fig. 15).

Fig. 15
figure 15

µCT cross section of the ash sample treated with PEG 400 and 4000 and freeze dried (As1-PEG2) with cracks in, and collapse of, the wood structure

Polyethylene glycol (PEG 400, 1500 and 4000) three-step and freeze-drying

The samples conserved in three stages with PEG 400, PEG 1500 and PEG 4000 and then freeze-dried are among the best results of the methods with PEG (Appendix B). With the exception of two samples, the ASE values are above 90%. The samples with poorer values are the oak sample (Oa1-PEG3) with a value of 85% and the pine sample (Pi1-PEG3) with a value of 80%. The scans after 10 years show satisfactory volume stability (Appendix C). As with the other conservation methods using PEG, the µCT data show good volume stabilisation with a simultaneous increase in surface area inside the samples, again indicating the formation of fine cracks (Appendix D). The µCT cross-sections (Fig. 16) confirm that these cracks occur in all samples conserved with the three-step PEG method except the fir sample (Fi1-PEG3). In particular, the alder sample (Al1-PEG3) stands out with a shrinkage of almost 7% and a surface area increase of over 600%. This sample is an exception among the samples conserved with PEG because, in addition to the cracks, there is also considerable collapse in the conserved wood structure (Fig. 17).

Fig. 16
figure 16

µCT cross section of the ash sample treated with PEG (three-step) and freeze dried (As1-PEG3) with cracks in the wood structure

Fig. 17
figure 17

µCT cross section of the alder sample treated with PEG (three-step) and freeze dried (Al1-PEG3) with cracks in, and collapse of, the wood structure

Saccharose

The samples conserved with saccharose show a poorer conservation overall and the results vary greatly. Thus, the ASE of the ten samples directly after conservation ranges between 64% and 94%, with only the fir sample (Fi1-Sac) with 94% and the pine sample (Pi1-Sac) with 90% showing a value above 90% (Appendix B). The ASE of the pine sample (Pi1-Sac) is particularly remarkable in this context, as the other conservation methods consistently perform rather poorly in this series of samples. A change in volume after ten years is also not observed in the wood samples conserved with saccharose (Fig. 7). The µCT data also show very different results, with very poor values of volume stabilisation inside the samples in some cases (Al1-Sac, As1-Sac, Oa3-Sac, Appendix C). Together with the high values of surface change (Appendix D), this indicates a significant collapse of the wood structure, as confirmed by the images of the ash sample (As1-Sac, Fig. 18). However, low stabilisation is not solely related to low concentration of consolidant. Highly concentrated solutions can also be problematic. Their susceptibility to degradation by osmotolerant microorganisms can lead to the development of slime and gases, which can prevent consolidants from penetrating the wood. Even an excess of biocides, due to the low penetration of the same, could not prevent these fermentation processes. The decomposition of saccharose takes place by chemical or microbiological processes, whereby the sugar is converted into the monosaccharides of fructose and glucose. This prevents volume stabilisation and, as the degradation products are more hygroscopic, leads to a damp surface and poorer drying [84,85,86].

Fig. 18
figure 18

µCT cross section of the ash sample treated with saccharose (As1-Sac) with collapse of the wood structure

Silicone oil

The samples conserved with silicone oil tend to show poorer volume stabilisation overall and the ASE of the samples is between 71% and 89% (Appendix B). No change in volume can be observed in the wood conserved with silicone oil after ten years (Fig. 7). As with the saccharose-conserved samples, the µCT data show very different results (Appendix C). Thus, there are also striking samples (Al1-Sil, As1-Sil, Sp1-Sil) with poor volume stabilisation and an interior surface enlargement, which again indicates the collapse of the wood structure (Appendix D). This is also confirmed, for example, by the images of sample As1-Sil (Fig. 19).

Fig. 19
figure 19

µCT cross section of the ash sample treated with silicone oil (As1-Sil) with collapse of the wood structure

Conclusion

On the basis of the surface data from structured-light 3D scanning of ten test series with a total of 83 wood samples, it was possible to comparatively investigate the preservation results of different conservation methods with regard to their volume stabilisation. Wood is a very heterogeneous material and the successful conservation and volume stabilisation depends on different factors. This study showed that first of all the state of preservation is of great importance. The dimensional changes upon air-drying are dependent on the water content. This was also confirmed by other studies [2, 5, 13, 80].

There are also enormous differences between the conservation methods studied. It should be noted that all methods investigated in the study stabilised the wood to some extent, in contrast to air-drying. The investigation of the volume stability after 10 years further showed that all conserved samples remained stable in contrast to the air-dried samples. However, it should also be noted that only the methods using PEG, alcohol-ether-resin and Kauramin 800® guarantee reliable volume stabilisation. The other methods were subject to considerable fluctuations and in some cases showed a large volume loss due to cell collapse.

For the first time, the internal structures of a large sample series were considered by the application of µCT. In contrast to the structured-light 3D scans performed here, the µCT measurements show the considerable damage such objects can take during conservation due to cracks and cell collapse. Such disadvantages could also be observed in samples that were treated with the methods using PEG, alcohol-ether-resin and Kauramin 800®. For example, in a condition with two differently degraded areas in the wood, large gaps can form during conservation with Kauramin 800®. This is possibly due to the fact that the conservation agent has the ability to stabilise heavily degraded wood better than well preserved wood, which may be explained by poorer penetration into well preserved wood [17, 87]. In the samples conserved with PEG and subsequently freeze-dried, a large number of fine cracks in the wood were very often visible in the µCT data. This can be explained by the fact that the aqueous PEG solution expands during freezing, resulting in damage to the wood structure. The two-step method using aqueous solutions of PEG 400 and PEG 4000 showed slightly better results with fewer cracks. This may be attributed to the fact that low molecular weight PEG lowers the critical freeze-drying temperature and a proportion of the solution does not freeze. Though less volume expansion may occur [46]. In addition, it was observed in one sample that there is considerable collapse in the centre. That may be explained by the fact that the aqueous solution of PEG thawed during the freeze-drying process. Afterwards, the wood structure collapsed when drying from the liquid phase. It is likely the conservation agent was transported to the outside areas by capillary forces, thus, appearing as though there is no conservation agent present in this area in the µCT data. This has already been described in the literature as being a crucial parameter in the conservation treatment with PEG [17, 18, 54, 58].

These observations show the importance of tomographic methods and the need to take into account the internal structures when assessing the conservation result. However, these observations also show that further research and validation of the results is required. In order to be able to assess the changes in the wood caused by the conservation with certainty, it is necessary in further test series to also record the preliminary condition of the samples using tomographic methods. However, in the case of the waterlogged condition of wood, it should be noted that the presence of water in the wood reduces the quality of the µCT data and complicates the measurement procedure. Therefore, for waterlogged wood, magnetic resonance imaging, for example, would be a suitable method to better capture the preliminary wet condition [55, 88, 89]. It should be mentioned that in this study only volume stabilisation of conservation methods was considered for evaluation. Other factors such as reversibility, effort, toxicity of the ingredients and long-term stability are also of great importance in the choice of the procedure.

Availability of data and materials

The datasets generated and/or analysed during the current study are available in the repository of the RGZM, [www.rgzm.de/kur]. Further datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

References

  1. Nilsson T, Rowell R. Historical wood—structure and properties. J Cult Herit. 2012;13:5–9.

    Article  Google Scholar 

  2. Hoffmann P. Conservation of archaeological ships and boats: personal experiences. London: Archetype Publications; 2013.

    Google Scholar 

  3. Fengel D, Wegener G. Wood: chemistry, ultrastructure, reactions. Remagen: Verlag Kessel; 2003.

    Google Scholar 

  4. Kim YS, Singh AP. Micromorphological characteristics of wood biodegradation in wet environments: a review. IAWA J. 2000;21:135–55.

    Article  Google Scholar 

  5. Hoffmann P, Jones MA. Structure and degradation process for waterlogged archaeological wood. In: Rowell RM, Barbour J, editors. Archaeological wood; properties, chemistry and preservation. Washington, DC: American Chemical Society; 1990. p. 35–65.

    Google Scholar 

  6. Blanchette RA. A review of microbial deterioration found in archaeological wood from different environments. Int Biodeterior. 2000;46:189–204.

    Article  Google Scholar 

  7. Björdal CG. Microbial degradation of waterlogged archaeological wood. J Cult Herit. 2012;13:118–22.

    Article  Google Scholar 

  8. Grattan DW. Waterlogged wood. In: Pearson C, editor. Conservation of marine archaeological objects. Oxford: Butterworth-Heinemann; 1987. p. 55–67.

    Chapter  Google Scholar 

  9. High KE, Penkman KEH. A review of analytical methods for assessing preservation in waterlogged archaeological wood and their application in practice. Herit Sci. 2020;8:1–33.

    Article  Google Scholar 

  10. Schniewind AP. Physical and mechanical properties of archaeological wood. In: Rowell RM, Barbour J, editors. Archaeological wood; properties, chemistry and preservation. Washington D.C: American Chemical Society; 1990. p. 87–109.

    Google Scholar 

  11. Barbour RJ, Leney L. Shrinkage and collapse in waterlogged archaeological wood: Contribution III, Hoko River Series. In: Grattan DW, McCawley JC. editors. Proceedings of the ICOM-CC waterlogged wood working group conference, Ottawa, 1981. Ottawa: ICOM-CC; 1982. p. 208–25.

  12. Hawley OF. Wood-liquid relations. Technical bulletin, no. 248. Washington: United States Department of Agriculture, 1931.

  13. Christensen BB. Om Konservering af Mosefundne Trægenstande. In: Kongelike Nordiske Oldskriftselskan, editor. Aarbøger for Nordisk Oldkyndighed og Historie 1951. Copenhagen: Nordisk Forlag; 1952. p. 22–62.

    Google Scholar 

  14. Grattan DW, Clarke RW. Conservation of waterlogged wood. In: Pearson C, editor. Conservation of marine archaeological objects. Oxford: Butterworth-Heinemann; 1987. p. 164–206.

    Chapter  Google Scholar 

  15. Grattan DW, McCawley JC. The potential of the canadian winter climate for the freeze-drying of degraded waterlogged wood. Stud Conserv. 1978;23:157–67.

    Google Scholar 

  16. Grattan DW. A practical comparative study of several treatments for waterlogged wood. Stud Conserv. 1982;27:124–36.

    CAS  Google Scholar 

  17. Hoffmann P. On the efficiency of stabilisation methods for large waterlogged wooden objects, and on how to choose a method. In: Straetkver K, Huisman DJ, editors. Proceedings of the 10th ICOM-CC Group on wet organic archaeological materials conference, Amsterdam, 2007. Amersfoort: Rijksdienst Voor Archeologie, Cultuurlandschap En Monumenten; 2009. p. 323–50.

  18. Bräker OU, Bill J, Mühlethaler B, Schoch W, Schweingruber FH, Haas A. Zum derzeitigen Stand der Nassholzkonservierung. Diskussion der Grundlagen und Resultate eines von Fachlaboratorien 1976–1978 durchgeführten Methodenvergleiches. Zeitschr f Schweiz Archaeol Kunstgesch. 1979;36:97–145.

    Google Scholar 

  19. Christensen BB. Developments in the treatment of waterlogged wood in the National Museum of Denmark during the years 1962–69. Stud Conserv. 1971;16:27–44.

    Article  Google Scholar 

  20. International Council of Museums. ICOM code of ethics for museums. Paris: ICOM; 2017.

    Google Scholar 

  21. Florian M-LE. Scope and history of archaeological wood. In: Rowell RM, Barbour J, editors. Archaeological wood; properties, chemistry and preservation. Washington: American Chemical Society; 1990. p. 3–32.

    Google Scholar 

  22. Jenssen V. Conservation of wet organic artefacts excluding wood. In: Pearson C, editor. Conservation of marine archaeological objects. Oxford: Butterworth-Heinemann; 1987. p. 122–63.

    Chapter  Google Scholar 

  23. Herbst CF. Om bevaring af oldsager af træ fundne i törvemoser. Antiquarisk tidsskrift. Kjøbenhavn: Det kongelige nordiske oldskriftselskab; 1861. p. 174–6.

  24. Rathgen F. Die Konservierung von Altertumsfunden, Teil 2/3: Metalle und Metallegierungen, organische Stoffe: Mit Berücksichtigung ethnographischer und kunstgewerblicher Sammlungsgegenstände. Berlin: De Gruyter; 1924.

    Book  Google Scholar 

  25. Organ RM. Carbowax and other materials in the treatment of water-logged paleolithic wood. Stud Conserv. 1959;4:96–105.

    Google Scholar 

  26. Parrent JM. The conservation of waterlogged wood using sucrose. Stud Conserv. 1985;30:63–72.

    CAS  Google Scholar 

  27. Rosenqvist AM. The stabilizing of wood found in the Viking ship of Oseberg, Pt. II. Stud Conserv. 1959;4:62–72.

    CAS  Google Scholar 

  28. Broda M, Dąbek I, Dutkiewicz A, Dutkiewicz M, Popescu C-M, Mazela B, et al. Organosilicons of different molecular size and chemical structure as consolidants for waterlogged archaeological wood—a new reversible and retreatable method. Sci Rep. 2020;10:1–13.

    Article  CAS  Google Scholar 

  29. Walsh Z, Janeček E-R, Hodgkinson JT, Sedlmair J, Koutsioubas A, Spring DR, et al. Multifunctional supramolecular polymer networks as next-generation consolidants for archaeological wood conservation. Proc Natl Acad Sci. 2014;111:17743–8.

    Article  CAS  Google Scholar 

  30. Walsh Z, Janeček E-R, Jones M, Scherman OA. Natural polymers as alternative consolidants for the preservation of waterlogged archaeological wood. Stud Conserv. 2017;62:173–83.

    Article  CAS  Google Scholar 

  31. McHale E, Steindal CC, Kutzke H, Benneche T, Harding SE. In situ polymerisation of isoeugenol as a green consolidation method for waterlogged archaeological wood. Sci Rep. 2017;7:1–9.

    Article  Google Scholar 

  32. Christensen M, Kutzke H, Hansen FK. New materials used for the consolidation of archaeological wood–past attempts, present struggles, and future requirements. J Cult Herit. 2012;13:183–90.

    Article  Google Scholar 

  33. Broda M, Hill CAS. Conservation of waterlogged wood—past, present and future perspectives. Forests. 2021;12:1193.

    Article  Google Scholar 

  34. Babiński L. Dimensional changes of waterlogged archaeological hardwoods pre-treated with aqueous mixtures of lactitol/trehalose and mannitol/trehalose before freeze-drying. J Cult Herit. 2015;16:876–82.

    Article  Google Scholar 

  35. Nguyen TD, Sakakibara K, Imai T, Tsujii Y, Kohdzuma Y, Sugiyama J. Shrinkage and swelling behavior of archaeological waterlogged wood preserved with slightly crosslinked sodium polyacrylate. J Wood Sci. 2018;64:294–300.

    Article  CAS  Google Scholar 

  36. Nguyen TD, Wakiya S, Matsuda K, Ngoc BD, Sugiyama J, Kohdzuma Y. Diffusion of chemicals into archaeological waterlogged hardwoods obtained from the Thang Long Imperial Citadel site, Vietnam. J Wood Sci. 2018;64:836–44.

    Article  CAS  Google Scholar 

  37. Imazu S, Ito K, Fujita H, Morgos A. The rapid trehalose conservation method for archaeological waterlogged wood and laquerware. In: Grant T. Cook C. editors. Proceedings of the 12th ICOM-CC Group on wet organic archaeological materials conference, Istanbul, 2013. Istanbul: Lulu.com; 2016. p. 110–7.

  38. Jensen P, Pedersen NB. Examination of D-mannitol as an impregnation agent for heavily degraded waterlogged archaeological wood. In: Grant T. Cook C. editors. Proceedings of the 12th ICOM-CC Group on wet organic archaeological materials conference, Istanbul, 2013. Istanbul: Lulu.com; 2016. p. 118–25.

  39. Broda M, Spear MJ, Curling SF, Ormondroyd GA. The viscoelastic behaviour of waterlogged archaeological wood treated with methyltrimethoxysilane. Materials. 2021;14:5150.

    Article  CAS  Google Scholar 

  40. Majka J, Zborowska M, Fejfer M, Waliszewska B, Olek W. Dimensional stability and hygroscopic properties of PEG treated irregularly degraded waterlogged Scots pine wood. J Cult Herit. 2018;31:133–40.

    Article  Google Scholar 

  41. Vetter LD, den Bulcke JV, Acker JV. Impact of organosilicon treatments on the wood-water relationship of solid wood. Holzforschung. 2010;64:463–8.

    Article  Google Scholar 

  42. Broda M, Mazela B. Application of methyltrimethoxysilane to increase dimensional stability of waterlogged wood. J Cult Herit. 2017;25:149–56.

    Article  Google Scholar 

  43. Kilic M, Kilic AG. Kauramin tests for the Yenikapi shipwrecks. In: Grant T. Cook C. editors. Proceedings of the 12th ICOM-CC Group on wet organic archaeological materials conference, Istanbul, 2013. Istanbul: Lulu.com; 2016. p. 222–7.

  44. Babiński L. Influence of pre-treatment on shrinkage of freeze-dried archaeological oak-wood. Acta Sci Pol Silv Colendar Rat Ind Lignar. 2007;6:89–99.

    Google Scholar 

  45. www.rgzm.de/kur.

  46. Stelzner I. Zur Nassholzkonservierung Bestimmung prozessrelevanter Eigenschaften für die Gefriertrocknung. Stuttgart: Staatliche Akademie der Bildenden Künste; 2017. https://doi.org/10.11588/artdok.00005438. Accessed 12 Oct 2021.

    Book  Google Scholar 

  47. Wittköpper M, Muskalla W, Stephan B, Le Boedec-Moesgard A, Gebhadt S, Klonk S. In: The KUR (conservation and restauration) project - a comparison of different methods to preserve waterlogged wood. Proceedings of the 12th ICOM-CC Group on wet organic archaeological materials conference, Istanbul, 2013. Istanbul: Lulu.com; 2016. p. 134–43.

  48. Cook C, Lafrance J, Li C. Preliminary assessment of a new PEG. In: Strætkvern, K. Williams. E. editors. Proceedings of th 11th ICOM-CC Group on wet organic archaeological materials conference, Greenville, 2010. Greenville: Lulu.com; 2010. p. 245–55.

  49. Cretté SA, Näsänen L, González-Pereyra NG, Rennison B. Conservation and treatment monitoring of waterlogged archeological corks using supercritical CO2 and treatment monitoring using structured-light 3D scanning. J Supercrit Fluids. 2013;79:199–313.

    Article  CAS  Google Scholar 

  50. Schindelholz E, Blanchette RA, Held BW, Jurgens J, Cook D, Drews MJ, Hand S, Seifert B. An evaluation of supercritical drying and PEG/freeze drying of waterlogged archaeological wood. In: Straetkver K, Huisman DJ. editors. Proceedings of the 10th ICOM-CC Group on wet organic archaeological materials conference, Amsterdam, 2007. Amersfoort: Rijksdienst Voor Archeologie, Cultuurlandschap En Monumenten; 2009. p. 399–416.

  51. De Jong J. Conservation techniques for old waterlogged wood from shipwrecks found in the Netherlands. Biodeterior Invest Tech. 1977;113:295–338.

    Google Scholar 

  52. Stelzner I. Transfer into praxis. Evaluation of consolidants for freeze-drying archaeological wood. In: Williams E, Hocker E. editors. Proceedings of th 13th ICOM-CC Group on wet organic archaeological materials conference, Florence, 2016. Florence: Lulu.com; 2018. p. 325–32.

  53. Van Damme T, Auer J, Ditta M, Grabowski M, Couwenberg M. The 3D annotated scans method: a new approach to ship timber recording. Herit Sci. 2020;8:1–18.

    Google Scholar 

  54. Braovac S, McQueen CMA, Sahlstedt M, Kutzke H, Łucejko JJ, Klokkernes T. Navigating conservation strategies: linking material research on alum-treated wood from the Oseberg collection to conservation decisions. Herit Sci. 2018;6:1–16.

    Article  Google Scholar 

  55. Kowalczuk J, Rachocki A, Broda M, Mazela B, Ormondroyd GA, Tritt-Goc J. Conservation process of archaeological waterlogged wood studied by spectroscopy and gradient NMR methods. Wood Sci Technol. 2019;53:1207–22.

    Article  CAS  Google Scholar 

  56. Bugani S, Modugno F, Łucejko JJ, Giachi G, Cagno S, Cloetens P, et al. Study on the impregnation of archaeological waterlogged wood with consolidation treatments using synchrotron radiation microtomography. Anal Bioanal Chem. 2009;395:1977–85.

    Article  CAS  Google Scholar 

  57. Rankin K, Hazell Z, Middleton A, Mavrogordato M. Micro-focus X-ray CT scanning of two rare wooden objects from the wreck of the London, and its application in heritage science and conservation. J Archaeol Sci. 2021;39:103158.

    Google Scholar 

  58. Wiesner I, Stelzner J, Million S, Kuhnt K, Bott K. The first wheels go round again. In: Grant T. Cook C. editors. Proceedings of the 12th ICOM-CC group on wet organic archaeological materials conference, Istanbul, 2013. Istanbul: Lulu.com; 2016. p. 197–8.

  59. Unger A, Planitzer J, Morgós A. Röntgencomputer- und Magnetresonanztomographie zur Charakterisierung von archäologischem Naßholz. Holztechnologie. 1988;29:249–50.

    Google Scholar 

  60. Demoulin T, Gebhard R, Schillinger B. Neutron tomography of archaeological waterlogged wood. Restaur Archäol. 2015;7:27–33.

    Google Scholar 

  61. Christensen M, Hansen FK, Kutzke H. Phenol formaldehyde revisited-novolac resins for the treatment of degraded archaeological wood: novolac resins for treatment of degraded archaeological wood. Archaeometry. 2015;57:536–59.

    Article  CAS  Google Scholar 

  62. Stelzner I, Stelzner J, Martinez-Garcia J, Gwerder D, Wittkoepper M, Muskalla W, Egg M. Schuetz P. Non-destructive assessment of conserved archaeological wood using computed tomography. In: Bridgland J, editor. Transcending boundaries: integrated approaches to conservation. ICOM-CC 19th Triennial Conference preprints, Beijing, 2021. Paris: ICOM-CC; 2021; p. 1–11.

  63. Wittköpper M. Der aktuelle Stand der Konservierung archäologischer Naßhölzer mit Melamin/Aminoharzen am Römisch-Germanischen Zentralmuseum. Arbeitsblätter für Restauratoren. 1998;29:227–83.

    Google Scholar 

  64. Imazu S, Morgós A. An improvement on the Lactitol MC conservation method used for the conservation of archaeological waterlogged wood (The conservation method using Lactitol MC and Trehalose mixture). In: Hoffmann P, Spriggs JA, Grant T, Cook C, Recht A, editors. Proceedings of the 8th ICOM-CC Group on wet organic archaeological materials conference, Stockholm, 2001. Bremerhaven: ICOM-CC; 2002. p. 413–28.

  65. Smith CW. Archaeological conservation using polymers: practical applications for organic artifact stabilization. College Station: Texas A&M University Press; 2003.

    Google Scholar 

  66. Jensen P, Petersen AH, Straetkvern K. From the Skuldelev to the Roskilde ships—50 years of shipwreck conservation at the National Musem of Denmark. In: Ek M, editor. Shipwrecks 2011 proceedings, chemistry and preservation of waterlogged wooden shipwrecks, Stockholm, 2011. Stockholm: Royal Institute of Technology; 2011. p. 14–20.

    Google Scholar 

  67. Cook C, Grattan D. A method of calculation the concentration of PEG for freeze-drying waterlogged wood. In: Hoffmann P, editor. Proceedings of the 4th ICOM-CC Group on wet organic archaeological materials conference, Bremerhaven, 1987. Bremerhaven: ICOM-CC; 1990. p. 239–52.

  68. Kellogg RM, Sastry CBR, Wellwood RW. Relationships between cell-wall composition and cell-wall density. Wood Fiber Sci. 1975;7:170–7.

    Google Scholar 

  69. Macchioni N, Pizzo B, Capretti C, Giachi G. How an integrated diagnostic approach can help in a correct evaluation of the state of preservation of waterlogged archaeological wooden artefacts. J Archaeol Sci. 2012;39:3255–63.

    Article  CAS  Google Scholar 

  70. Macchioni N, Pecoraro E, Pizzo B. The measurement of maximum water content (MWC) on waterlogged archaeological wood: a comparison between three different methodologies. J Cult Herit. 2018;30:51–6.

    Article  Google Scholar 

  71. Brather S. Zur Anwendung von Dichteangaben bei der Bestimmung der PEG-Tränkkonzentration mit dem PEGcon-Computerprogramm. Restaur Archäol. 2009;2:91–7.

    Google Scholar 

  72. Feldkamp LA, Davis LC, Kress JW. Practical cone-beam algorithm. J Opt Soc Am A. 1984;1:612–9.

    Article  Google Scholar 

  73. Stelzner J, Million S. X-ray Computed Tomography for the anatomical and dendrochronological analysis of archaeological wood. J Archaeol Sci. 2015;55:188–96.

    Article  Google Scholar 

  74. Stamm AJ, Tarkow H. Dimensional Stabilisation of Wood. J Phys Colloid Chem. 1947;51:493–505.

    Article  CAS  Google Scholar 

  75. Stamm AJ, Burr HK, Kline AL. Heat-stabilized Wood (staybwood). Madison: Forest Products Laboratory; 1955.

    Google Scholar 

  76. Stamm AJ. Effect of Polyethylene Glycol on the Dimensional Stability of Wood. For Prod J. 1959;9:375–81.

    CAS  Google Scholar 

  77. Rowell RM, Youngs RL. Dimensional stabilization of wood in use. Madison: Forest Products Laboratory; 1981.

    Book  Google Scholar 

  78. Håfors B. The role of the wasa in the development of the polyethylene glycol preservation method. In: Rowell RM, Barbour J, editors. Archaeological wood; properties, chemistry and preservation. Washington, DC: American Chemical Society; 1990. p. 195–233.

    Google Scholar 

  79. Wadell H. Volume, shape and roundness of quartz particles. J Geol. 1935;43:250–80.

    Article  Google Scholar 

  80. de Jong J. The conservation of shipwrecks. In: ICOM-CC, editor. Preprints of the ICOM-CC 5th triennial meeting, Zagreb, 1978. Paris: ICOM-CC; 1978. p. 78/7/1–10.

  81. de Jong J. The conservation of waterlogged timber at Ketelhaven (Holland). In: ICOM-CC, editor. Preprints of the ICOM-CC 5th triennial meeting, Venice, 1975. Paris: ICOM-CC; 1975. p. 75/8/1–9.

  82. Mühlethaler B. Conservation of waterlogged wood and wet leather. Paris: Eyrolles; 1973.

    Google Scholar 

  83. Jensen P, Jørgensen G, Schnell U. Dynamic LV-SEM analyses of freeze drying processes for waterlogged wood. In: Hoffmann P, Grant T, Spriggs JA, Cook C, Recht A, editors. Proceedings of the 8th ICOM-CC Group on wet organic archaeological materials conference, Stockholm, 2001. Bremerhaven: ICOM-CC; 2002. p. 319–33.

  84. Hoffmann P. On the long-term visco-elastic behaviour of polyethylene glycol (PEG) impregnated archaeological oak wood. Holzforschung. 2010;64:725–8.

    Article  CAS  Google Scholar 

  85. Mietke H, Martin D. Sugar preservation of the Friesland ship. Chemical and microbiological investigations and insights. In: Bonnot-Diconne C, Hiron X, Khoi Tran Q, Hoffmann P, editors. Proceedings of the 7th ICOM-CC Group on wet organic archaeological materials conference, Grenoble, 1998. Grenoble: ICOM-CC; 1999. p. 204–9.

  86. Schiweck H. Zucker/Saccharose, Seine anwendungstechnisch relevanten Eigenschaften bei der Nassholzkonservierung. Arbeitsblätter für Restauratoren. 1998;31:241–6.

    Google Scholar 

  87. Spinella A, Chillura Martino DF, Saladino ML, et al. Solid state NMR investigation of the roman Acqualadroni rostrum: tenth year assessment of the consolidation treatment of the wooden part. Cellulose. 2021;28:1025–38.

    Article  CAS  Google Scholar 

  88. Cole-Hamilton DI, Kaye B, Chudek IA, Hunter G. Nuclear magnetic resonance imaging of waterlogged wood. Stud Conserv. 1995;40:41–50.

    Google Scholar 

  89. Mori M, Kuhara S, Kobayashi K, Suzuki S, Yamada M, Senoo A. Non-destructive tree-ring measurements using a clinical 3T-MRI for archaeology. Dendrochronologia. 2019;57:125630.

    Article  Google Scholar 

Download references

Acknowledgements

The authors thank the Federal Cultural Foundation and the Cultural Foundation of German States (KUR Programme) and all participants for their work in conserving the wooden samples.

The 3D scanning was done in cooperation with the University of Applied Science Mainz, i3mainz—Institute for Spatial Information and Surveying Technology.

Funding

Open Access funding enabled and organized by Projekt DEAL. The establishment of the reference collection for the conservation of waterlogged wood was funded by the Federal Cultural Foundation and the Cultural Foundation of German States. The cross-border research project is funded by the German Research Foundation—416877131 and the Swiss National Science Foundation—200021E_183684.

Author information

Authors and Affiliations

Authors

Contributions

JS designed, analysed and interpreted the data regarding the surface/shrinkage analyses of archaeological wood and was the major contributor in writing the manuscript. IS designed, analysed and interpreted the data and wrote the manuscript. DG performed the CT measurements. AC, GH were responsible for the structured-light 3D scanning. MW, WM, ME were responsible for the preparation of the KUR sample collection. DG, JM, MW, WM, AC, GH, ME, PS supported the analysis of the data as well as contributed to the manuscript writing. All authors read and approved the final manuscript.

Corresponding author

Correspondence to Jörg Stelzner.

Ethics declarations

Competing interests

The authors declare that they have no competing interests.

Additional information

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Appendices

Appendices

Appendix A: Genus, conservation method, condition, dimensions and resolution µCT of the samples

Sample

KUR-No

Genus

Conservation method

Umax (%)

Condition (de Jong)

Basic density (g/cm3)

Residual basic density (%)

Dimensions (cm)

L, Ø/L, W, H

Resolution µCT (µm)

Al1-Air

V24-23

Alder

Air dried

743

1

0.124

28

20, 3–5

27

Al1-AlEt

V24-45

Alder

Alcohol-Ether

706

1

0.129

29

12, 3–5

27

Al1-K800

V24-60

Alder

Kauramin 800®

958

1

0.098

22

16, 3–5

30

Al1-LaTr

V24-19

Alder

Lactitol/trehalose

891

1

0.104

24

14, 3–5

30

Al1-PEG1

V24-13

Alder

PEG (1)

853

1

0.109

25

17, 3–5

35

Al1-PEG2

V24-63

Alder

PEG (2)

671

1

0.136

31

18, 3–5

27

Al1-PEG3

V24-21

Alder

PEG (3)

1048

1

0.090

20

19, 3–5

30

Al1-Sac

V24-34

Alder

Saccharose

820

1

0.113

26

13, 3–5

27

Al1-Sil

V24-56

Alder

Silicone oil

807

1

0.114

26

15, 3–5

30

As1-Air

V28-27

Ash

Air dried

738

1

0.124

22

11, 12

43

As1-AlEt

V28-23

Ash

Alcohol-Ether

994

1

0.094

17

11, 12

44

As1-K800

V28-30

Ash

Kauramin 800®

961

1

0.097

17

11, 12

35

As1-PEG1

V28-08

Ash

PEG (1)

1291

1

0.074

13

11, 12

35

As1-PEG2

V28-10

Ash

PEG (2)

1195

1

0.079

14

11, 12

35

As1-PEG3

V28-36

Ash

PEG (3)

929

1

0.100

18

11, 12

44

As1-Sac

V28-07

Ash

Saccharose

1376

1

0.069

12

11, 12

35

As1-Sil

V28-24

Ash

Silicone oil

983

1

0.095

17

11, 12

35

Be1-Air

V07-23

Beech

Air dried

664

1

0.137

24

20, 8, 8

35

Be1-AlEt

V07-18

Beech

Alcohol-Ether

735

1

0.125

22

12, 8, 8

35

Be1-K800

V07-14

Beech

Kauramin 800®

720

1

0.127

23

19, 8, 8

35

Be1-LaTr

V07-Exp3

Beech

Lactitol/trehalose

566

1

0.158

28

17, 8, 8

35

Be1-PEG1

V07-09

Beech

PEG (1)

772

1

0.119

21

13, 8, 8

35

Be1-PEG2

V07-27

Beech

PEG (2)

654

1

0.139

25

14, 8, 8

35

Be1-PEG3

V07-08

Beech

PEG (3)

747

1

0.123

22

15, 8, 8

35

Be1-Sac

V07-01

Beech

Saccharose

748

1

0.123

22

16, 8, 8

35

Be1-Sil

V07-37

Beech

Silicone oil

808

1

0.114

20

18, 8, 8

35

Fi1-Air

V22-28

Fir

Air dried

381

2

0.223

59

30, 8, 2,5

32

Fi1-AlEt

V22-09

Fir

Alcohol-Ether

398

2

0.215

57

22, 8, 2,5

32

Fi1-K800

V22-33

Fir

Kauramin 800®

487

1

0.181

48

26, 8, 2,5

32

Fi1-LaTr

V22-26

Fir

Lactitol/trehalose

352

2

0.239

63

24, 8, 2,5

32

Fi1-PEG1

V22-22

Fir

PEG (1)

432

1

0.201

53

27, 8, 2,5

32

Fi1-PEG2

V22-31

Fir

PEG (2)

3711

2

0.2281

601

28, 8, 2,5

32

Fi1-PEG3

V22-35

Fir

PEG (3)

241

2

0.325

86

29, 8, 2,5

32

Fi1-Sac

V22-11

Fir

Saccharose

285

2

0.284

75

23, 8, 2,5

32

Fi1-Sil

V22-05

Fir

Silicone oil

333

2

0.250

66

25, 8, 2,5

32

Fi2-Air

V30-Exp1

Fir

Air dried

465

1

0.188

49

11, 6–7

40

Fi2-AlEt

V30-33

Fir

Alcohol-Ether

695

1

0.131

35

11, 6–7

40

Fi2-K800

V30-09

Fir

Kauramin 800®

601

1

0.150

39

11, 6–7

40

Fi2-PEG1

V30-04

Fir

PEG (1)

542

1

0.164

43

11, 6–7

40

Fi2-PEG2

V30-18

Fir

PEG (2)

632

1

0.143

38

11, 6–7

40

Fi2-PEG3

V30-15

Fir

PEG (3)

554

1

0.161

42

11, 6–7

40

Fi2-Sac

V30-17

Fir

Saccharose

599

1

0.150

40

11, 6–7

40

Fi2-Sil

V30-24

Fir

Silicone oil

548

1

0.163

43

11, 6–7

40

Oa1-Air

V10-02

Oak

Air dried

201

2

0.374

67

17, 7

32

Oa1-K800

V10-06

Oak

Kauramin 800®

198

2

0.378

67

16, 7

32

Oa1-LaTr

V10-33

Oak

Lactitol/trehalose

160

3

0.441

79

15, 7

32

Oa1-PEG1

V10-29

Oak

PEG (1)

179

3

0.407

73

11, 7

32

Oa1-PEG2

V10-31

Oak

PEG (2)

176

3

0.412

74

12, 7

32

Oa1-PEG3

V10-39

Oak

PEG (3)

181

3

0.404

72

13, 7

32

Oa1-Sac

V10-03

Oak

Saccharose

163

3

0.435

78

14, 7

32

Oa2-Air

V16-15

Oak

Air dried

362

2

0.233

42

12, 15, 4,5

33

Oa2-AlEt

V16-09

Oak

Alcohol-Ether

175

3

0.414

74

12, 15, 4,5

32

Oa2-K800

V16-25

Oak

Kauramin 800®

228

2

0.339

61

12, 15, 4,5

44

Oa2-PEG1

V16-18

Oak

PEG (1)

189

2

0.391

70

12, 15, 4,5

35

Oa2-PEG2

V16-32

Oak

PEG (2)

237

2

0.329

59

12, 15, 4,5

44

Oa2-PEG3

V16-36

Oak

PEG (3)

188

2

0.393

70

12, 15, 4,5

35

Oa2-Sac

V16-17

Oak

Saccharose

184

3

0.399

71

12, 15, 4,5

35

Oa2-Sil

V16-13

Oak

Silicone oil

187

2

0.394

70

12, 15, 4,5

32

Oa3-Air

V27-17

Oak

Air dried

577

1

0.155

28

12–14, 5–6

19

Oa3-AlEt

V27-40

Oak

Alcohol-ether

527

1

0.168

30

12–14, 5–6

32

Oa3-K800

V27-07

Oak

Kauramin 800®

646

1

0.140

25

12–14, 5–6

26

Oa3-LaTr

V27-30

Oak

Lactitol/trehalose

566

1

0.158

28

12–14, 5–6

26

Oa3-PEG1

V27-12

Oak

PEG (1)

691

1

0.132

24

12–14, 5–6

32

Oa3-PEG2

V27-02

Oak

PEG (2)

578

1

0.155

28

12–14, 5–6

32

Oa3-PEG3

V27-01

Oak

PEG (3)

557

1

0.160

29

12–14, 5–6

39

Oa3-Sac

V27-21

Oak

Saccharose

434

1

0.200

36

12–14, 5–6

26

Oa3-Sil

V27-10

Oak

Silicone oil

520

1

0.170

30

12–14, 5–6

26

Pi1-Air

V03-01

Pine

Air dried

390

2

0.219

52

20, 7, 9–12

39

Pi1-AlEt

V03-17

Pine

Alcohol-Ether

3321

2

0.2511

601

12, 7, 9–12

40

Pi1-K800

V03-41

Pine

Kauramin 800®

3321

2

0.2511

601

19, 7, 9–12

40

Pi1-LaTr

V03-28

Pine

Lactitol/trehalose

3321

2

0.2511

601

17, 7, 9–12

40

Pi1-PEG1

V03-35

Pine

PEG (1)

3321

2

0.2511

601

13, 7, 9–12

40

Pi1-PEG2

V03-32

Pine

PEG (2)

3321

2

0.2511

601

14, 7, 9–12

40

Pi1-PEG3

V03-20

Pine

PEG (3)

3321

2

0.2511

601

15, 7, 9–12

40

Pi1-Sac

V03-45

Pine

Saccharose

3321

2

0.2511

601

16, 7, 9–12

40

Pi1-Sil

V03-42

Pine

Silicone oil

3321

2

0.2511

601

18, 7, 9–12

40

Sp1-Air

V23-20

Spruce

Air dried

503

1

0.176

46

21, 10, 6

40

Sp1-K800

V23-08

Spruce

Kauramin 800®

482

1

0.182

48

20, 10, 6

40

Sp1-LaTr

V23-02

Spruce

Lactitol/trehalose

454

1

0.192

51

19, 10, 6

40

Sp1-PEG1

V23-25

Spruce

PEG (1)

427

1

0.203

53

15, 10, 6

40

Sp1-PEG2

V23-30

Spruce

PEG (2)

280

2

0.288

76

16, 10, 6

40

Sp1-PEG3

V23-28

Spruce

PEG (3)

282

2

0.287

75

17, 10, 6

40

Sp1-Sac

V23-29

Spruce

Saccharose

374

2

0.227

60

18, 10, 6

40

  1. 1 = Mean value of the sample series

Appendix B: Volumes of the samples before and after conservation with calculated shrinkage and ASE

Sample

KUR-No

Volume Scan1 (mm3) before conservation

Volume Scan2 (mm3) after conservation

Shrinkage (%)

ASE (%)

Al1-Air

V24-23

146,308

31,179

78.69

0

Al1-AlEt

V24-45

102,902

99,115

3.68

95

Al1-K800

V24-60

160,907

162,261

− 0.84

101

Al1-LaTr

V24-19

128,825

104,028

19.25

76

Al1-PEG1

V24-13

224,601

223,555

0.47

99

Al1-PEG2

V24-63

105,005

104,819

0.18

95

Al1-PEG3

V24-21

159,932

156,425

2.19

97

Al1-Sac

V24-34

113,119

81,711

27.77

65

Al1-Sil

V24-56

154,675

140,245

9.33

88

As1-Air

V28-27

1,333,063

235,173

82.36

0

As1-AlEt

V28-23

1,243,400

1,205,707

3.03

96

As1-K800

V28-30

571,461

573,401

− 0.34

100

As1-PEG1

V28-08

731,204

755,998

− 3.39

104

As1-PEG2

V28-10

416,108

421,655

− 1.33

102

As1-PEG3

V28-36

1,121,247

1,145,266

− 2.14

103

As1-Sac

V28-07

757,823

604,063

20.29

75

As1-Sil

V28-24

1,220,413

1,099,338

9.92

88

Be1-Air

V07-23

772,702

151,476

80.40

0

Be1-AlEt

V07-18

597,620

565,700

5.34

93

Be1-K800

V07-14

689,166

688,499

0.10

100

Be1-LaTr

V07-Exp3

671,849

630,914

6.09

92

Be1-PEG1

V07-09

674,679

671,609

0.46

99

Be1-PEG2

V07-27

699,016

697,988

0.15

100

Be1-PEG3

V07-08

585,750

569,672

2.74

97

Be1-Sac

V07-01

609,858

434,048

28.83

64

Be1-Sil

V07-37

507,941

389,231

23.37

71

Fi1-Air

V22-28

453,549

222,550

50.93

0

Fi1-AlEt

V22-09

460,970

440,617

4.42

91

Fi1-K800

V22-33

384,611

371,581

3.39

93

Fi1-LaTr

V22-26

360,264

328,850

8.72

83

Fi1-PEG1

V22-22

494,810

478,138

3.37

93

Fi1-PEG2

V22-31

445,544

434,733

2.43

95

Fi1-PEG3

V22-35

500,516

483,497

3.40

93

Fi1-Sac

V22-11

480,933

465,727

3.16

94

Fi1-Sil

V22-05

434,348

392,397

9.66

81

Fi2-Air

V30-Exp1

88,000

49,539

43.71

0

Fi2-AlEt

V30-33

427,312

414,753

2.94

93

Fi2-K800

V30-09

495,437

492,590

0.57

99

Fi2-PEG1

V30-04

307,024

306,696

0.11

100

Fi2-PEG2

V30-18

269,965

270,071

− 0.04

100

Fi2-PEG3

V30-15

421,682

411,711

2.36

95

Fi2-Sac

V30-17

357,884

338,088

5.53

87

Fi2-Sil

V30-24

404,852

386,070

4.64

89

Oa1-Air

V10-02

725,355

399,675

44.90

0

Oa1-K800

V10-06

895,292

868,531

2.99

93

Oa1-LaTr

V10-33

768,421

705,640

8.17

82

Oa1-PEG1

V10-29

1,008,166

930,839

7.67

83

Oa1-PEG2

V10-31

997,903

883,538

11.46

74

Oa1-PEG3

V10-39

969,533

883,916

8.83

80

Oa1-Sac

V10-03

901,297

798,944

11.36

75

Oa2-Air

V16-15

512,214

249,991

51.19

0

Oa2-AlEt

V16-09

806,657

758,211

6.01

88

Oa2-K800

V16-25

1,214,955

1,160,158

4.51

91

Oa2-PEG1

V16-18

1,002,133

944,715

5.73

89

Oa2-PEG2

V16-32

1,258,876

1,188,430

5.60

89

Oa2-PEG3

V16-36

1,208,876

1,157,459

4.25

92

Oa2-Sac

V16-17

1,056,104

961,673

8.94

83

Oa2-Sil

V16-13

844,580

725,961

14.04

73

Oa3-Air

V27-17

293,261

47,476

83.81

0

Oa3-AlEt

V27-40

267,820

250,129

6.61

92

Oa3-K800

V27-07

340,889

338,726

0.63

99

Oa3-LaTr

V27-30

266,238

220,194

17.29

79

Oa3-PEG1

V27-12

363,884

362,077

0.50

99

Oa3-PEG2

V27-02

283,059

268,144

5.27

94

Oa3-PEG3

V27-01

289,788

266,534

8.02

90

Oa3-Sac

V27-21

316,392

249,489

21.15

75

Oa3-Sil

V27-10

379,014

325,680

14.07

83

Pi1-Air

V03-01

901,457

693,464

23.07

0

Pi1-AlEt

V03-17

771,098

727,558

5.65

76

Pi1-K800

V03-41

1,067,031

1,034,388

3.06

87

Pi1-LaTr

V03-28

776,356

755,903

2.63

89

Pi1-PEG1

V03-35

867,035

849,403

2.03

91

Pi1-PEG2

V03-32

983,539

953,583

3.05

87

Pi1-PEG3

V03-20

747,056

721,864

3.37

85

Pi1-Sac

V03-45

752,562

734,681

2.38

90

Pi1-Sil

V03-42

783,823

739,365

5.67

75

Sp1-Air

V23-20

1,062,100

365,165

65.62

0

Sp1-K800

V23-08

906,595

850,773

6.16

91

Sp1-LaTr

V23-02

839,765

768,510

8.49

87

Sp1-PEG1

V23-25

1,031,354

1,063,448

− 3.11

105

Sp1-PEG2

V23-30

955,998

944,487

1.20

98

Sp1-PEG3

V23-28

1,053,538

1,047,572

0.57

99

Sp1-Sac

V23-29

885,828

771,872

12.86

80

Appendix C: Volume changes of the samples 10 years after conservation considering inner structures from µCT

Sample

KUR-No

Volume Scan2 (mm3) after conservation

Volume Scan3 (mm3) 10 years after conservation

Volume µCT (mm3) 10 years after conservation

Shrinkage (%)

Scan 2 and 3

Shrinkage (%)

Scan 3 and µCT

Al1-Air

V24-23

31,179

24,760

17,706

20.59

28.49

Al1-AlEt

V24-45

99,115

98,384

93,231

0.74

5.24

Al1-K800

V24-60

162,261

161,185

156,812

0.66

2.71

Al1-LaTr

V24-19

104,028

102,996

86,192

0.99

16.31

Al1-PEG1

V24-13

223,555

223,018

217,914

0.24

2.29

Al1-PEG2

V24-63

104,819

102,585

100,481

2.13

2.05

Al1-PEG3

V24-21

156,425

154,216

143,465

1.41

6.97

Al1-Sac

V24-34

81,711

78,017

68,037

4.52

12.79

Al1-Sil

V24-56

140,245

139,209

132,425

0.74

4.87

As1-Air

V28-27

235,173

216,694

193,375

7.86

10.76

As1-AlEt

V28-23

1,205,707

1,197,414

1,184,689

0.69

1.06

As1-K800

V28-30

573,401

569,276

564,613

0.72

0.82

As1-PEG1

V28-08

755,998

754,140

744,974

0.25

1.22

As1-PEG2

V28-10

421,655

419,105

410,026

0.60

2.17

As1-PEG3

V28-36

1,145,266

1,147,825

1,137,275

− 0.22

0.92

As1-Sac

V28-07

604,063

597,524

512,904

1.08

14.16

As1-Sil

V28-24

1,099,338

1,089,794

939,898

0.87

13.75

Be1-Air

V07-23

151,476

147,738

127,144

2.47

13.94

Be1-AlEt

V07-18

565,700

559,303

558,498

1.13

0.14

Be1-K800

V07-14

688,499

686,595

677,402

0.28

1.34

Be1-LaTr

V07-Exp3

630,914

630,508

593,651

0.06

5.85

Be1-PEG1

V07-09

671,609

668,946

662,300

0.40

0.99

Be1-PEG2

V07-27

697,988

693,637

681,991

0.62

1.68

Be1-PEG3

V07-08

569,672

566,796

559,662

0.50

1.26

Be1-Sac

V07-01

434,048

433,702

427,680

0.08

1.39

Be1-Sil

V07-37

389,231

390,118

379,094

-0.23

2.83

Fi1-Air

V22-28

222,550

219,359

215,214

1.43

1.89

Fi1-AlEt

V22-09

440,617

437,768

434,591

0.65

0.73

Fi1-K800

V22-33

371,581

369,032

364,899

0.69

1.12

Fi1-LaTr

V22-26

328,850

326,867

326,097

0.60

0.24

Fi1-PEG1

V22-22

478,138

478,878

478,834

− 0.15

0.01

Fi1-PEG2

V22-31

434,733

436,025

433,782

− 0.30

0.51

Fi1-PEG3

V22-35

483,497

483,900

483,138

− 0.08

0.16

Fi1-Sac

V22-11

465,727

464,262

461,471

0.31

0.60

Fi1-Sil

V22-05

392,397

393,697

389,657

− 0.33

1.03

Fi2-Air

V30-Exp1

49,539

48,737

45,156

1.62

7.35

Fi2-AlEt

V30-33

414,753

413,424

409,599

0.32

0.93

Fi2-K800

V30-09

492,590

491,311

486,574

0.26

0.96

Fi2-PEG1

V30-04

306,696

305,457

298,768

0.40

2.19

Fi2-PEG2

V30-18

270,071

269,760

265,858

0.12

1.45

Fi2-PEG3

V30-15

411,711

412,560

403,988

− 0.21

2.08

Fi2-Sac

V30-17

338,088

336,763

330,397

0.39

1.89

Fi2-Sil

V30-24

386,070

385,594

384,166

0.12

0.37

Oa1-Air

V10-02

399,675

375,634

360,929

6.02

3.91

Oa1-K800

V10-06

868,531

852,548

760,510

1.84

10.80

Oa1-LaTr

V10-33

705,640

684,208

679,196

3.04

0.73

Oa1-PEG1

V10-29

930,839

925,324

922,177

0.59

0.34

Oa1-PEG2

V10-31

883,538

873,966

871,588

1.08

0.27

Oa1-PEG3

V10-39

883,916

884,323

863,624

− 0.05

2.34

Oa1-Sac

V10-03

798,944

800,842

798,595

− 0.24

0.28

Oa2-Air

V16-15

249,991

242,620

232,541

2.95

4.15

Oa2-AlEt

V16-09

758,211

746,747

746,471

1.51

0.04

Oa2-K800

V16-25

1,160,158

1,159,215

980,995

0.08

15.37

Oa2-PEG1

V16-18

944,715

944,951

927,353

− 0.02

1.86

Oa2-PEG2

V16-32

1,188,430

1,175,774

1,171,048

1.06

0.40

Oa2-PEG3

V16-36

1,157,459

1,148,261

1,131,193

0.79

1.49

Oa2-Sac

V16-17

961,673

965,032

960,526

− 0.35

0.47

Oa2-Sil

V16-13

725,961

723,683

722,258

0.31

0.20

Oa3-Air

V27-17

47,476

44,990

41,674

5.24

7.37

Oa3-AlEt

V27-40

250,129

245,888

243,032

1.70

1.16

Oa3-K800

V27-07

338,726

338,272

325,887

0.13

3.66

Oa3-LaTr

V27-30

220,194

220,472

189,715

− 0.13

13.95

Oa3-PEG1

V27-12

362,077

360,424

356,083

0.46

1.20

Oa3-PEG2

V27-02

268,144

266,536

258,136

0.60

3.15

Oa3-PEG3

V27-01

266,534

269,946

261,177

− 1.28

3.25

Oa3-Sac

V27-21

249,489

246,670

226,558

1.13

8.15

Oa3-Sil

V27-10

325,680

318,458

311,940

2.22

2.05

Pi1-Air

V03-01

693,464

690,464

669,462

0.43

3.04

Pi1-AlEt

V03-17

727,558

720,240

715,479

1.01

0.66

Pi1-K800

V03-41

1,034,388

1,029,360

1,024,444

0.49

0.48

Pi1-LaTr

V03-28

755,903

747,161

744,845

1.16

0.31

Pi1-PEG1

V03-35

849,403

848,117

844,877

0.15

0.38

Pi1-PEG2

V03-32

953,583

941,285

937,230

1.29

0.43

Pi1-PEG3

V03-20

721,864

723,021

720,784

− 0.16

0.31

Pi1-Sac

V03-45

734,681

736,946

733,326

− 0.31

0.49

Pi1-Sil

V03-42

739,365

745,165

738,476

− 0.78

0.90

Sp1-Air

V23-20

365,165

355,505

350,248

2.65

1.48

Sp1-K800

V23-08

850,773

842,600

821,603

0.96

2.49

Sp1-LaTr

V23-02

768,510

759,002

728,992

1.24

3.95

Sp1-PEG1

V23-25

1,063,448

1,059,582

1,053,036

0.36

0.62

Sp1-PEG2

V23-30

944,487

937,396

933,264

0.75

0.44

Sp1-PEG3

V23-28

1,047,572

1,048,511

1,045,822

− 0.09

0.26

Sp1-Sac

V23-29

771,872

766,530

745,213

0.69

2.78

Appendix D: Surface and volume changes of the samples 10 years after conservation considering inner structures from µCT

Sample

KUR-No

Surface Scan3 (mm2) 10 years after conservation

Surface µCT (mm2) 10 years after conservation

Surface change (%)

Scan 3 and µCT

Shrinkage (%)

Scan 3 and µCT

Al1-Air

V24-23

12,415

35,734

188

28.49

Al1-AlEt

V24-45

14,420

34,211

137

5.24

Al1-K800

V24-60

20,390

49,633

143

2.71

Al1-LaTr

V24-19

21,314

86,288

305

16.31

Al1-PEG1

V24-13

23,221

80,711

248

2.29

Al1-PEG2

V24-63

14,962

30,272

102

2.05

Al1-PEG3

V24-21

18,914

140,336

642

6.97

Al1-Sac

V24-34

16,940

37,182

119

12.79

Al1-Sil

V24-56

18,652

38,461

106

4.87

As1-Air

V28-27

35,082

119,044

239

10.76

As1-AlEt

V28-23

63,506

107,480

69

1.06

As1-K800

V28-30

44,077

87,917

99

0.82

As1-PEG1

V28-08

48,955

155,842

218

1.22

As1-PEG2

V28-10

37,882

96,622

155

2.17

As1-PEG3

V28-36

65,935

148,547

125

0.92

As1-Sac

V28-07

44,404

208,448

369

14.16

As1-Sil

V28-24

63,532

220,025

246

13.75

Be1-Air

V07-23

26,021

84,639

225

13.94

Be1-AlEt

V07-18

44,767

54,400

22

0.14

Be1-K800

V07-14

48,788

67,928

39

1.34

Be1-LaTr

V07-Exp3

48,653

168,337

246

5.85

Be1-PEG1

V07-09

48,109

119,721

149

0.99

Be1-PEG2

V07-27

49,745

132,591

167

1.68

Be1-PEG3

V07-08

43,384

73,579

70

1.26

Be1-Sac

V07-01

39,509

57,242

45

1.39

Be1-Sil

V07-37

37,812

70,962

88

2.83

Fi1-Air

V22-28

43,576

60,517

39

1.89

Fi1-AlEt

V22-09

53,868

66,645

24

0.73

Fi1-K800

V22-33

50,126

86,374

72

1.12

Fi1-LaTr

V22-26

50,801

67,624

33

0.24

Fi1-PEG1

V22-22

55,726

59,109

6

0.01

Fi1-PEG2

V22-31

56,394

78,984

40

0.51

Fi1-PEG3

V22-35

57,206

65,082

12

0.16

Fi1-Sac

V22-11

53,339

71,043

33

0.60

Fi1-Sil

V22-05

53,077

65,926

24

1.03

Fi2-Air

V30-Exp1

8635

19,131

122

7.35

Fi2-AlEt

V30-33

32,416

51,646

59

0.93

Fi2-K800

V30-09

37,876

86,145

127

0.96

Fi2-PEG1

V30-04

26,653

90,152

238

2.19

Fi2-PEG2

V30-18

26,381

71,852

172

1.45

Fi2-PEG3

V30-15

34,819

100,612

189

2.08

Fi2-Sac

V30-17

29,908

71,373

139

1.89

Fi2-Sil

V30-24

31,114

38,846

25

0.37

Oa1-Air

V10-02

52,255

85,432

63

3.91

Oa1-K800

V10-06

61,457

131,774

114

10.80

Oa1-LaTr

V10-33

57,718

102,110

77

0.73

Oa1-PEG1

V10-29

62,422

88,035

41

0.34

Oa1-PEG2

V10-31

58,833

81,532

39

0.27

Oa1-PEG3

V10-39

61,296

122,801

100

2.34

Oa1-Sac

V10-03

56,280

68,620

22

0.28

Oa2-Air

V16-15

35,080

59,160

69

4.15

Oa2-AlEt

V16-09

57,645

89,005

54

0.04

Oa2-K800

V16-25

81,202

198,276

144

15.37

Oa2-PEG1

V16-18

73,083

151,386

107

1.86

Oa2-PEG2

V16-32

80,898

134,853

67

0.40

Oa2-PEG3

V16-36

78,207

131,352

68

1.49

Oa2-Sac

V16-17

73,739

163,807

122

0.47

Oa2-Sil

V16-13

56,663

76,156

34

0.20

Oa3-Air

V27-17

11,681

23,883

104

7.37

Oa3-AlEt

V27-40

29,406

41,819

42

1.16

Oa3-K800

V27-07

31,023

62,587

102

3.66

Oa3-LaTr

V27-30

31,972

146,691

359

13.95

Oa3-PEG1

V27-12

31,420

49,818

59

1.20

Oa3-PEG2

V27-02

34,300

81,133

137

3.15

Oa3-PEG3

V27-01

32,071

62,450

95

3.25

Oa3-Sac

V27-21

37,746

101,695

169

8.15

Oa3-Sil

V27-10

36,179

47,156

30

2.05

Pi1-Air

V03-01

56,362

70,166

24

3.04

Pi1-AlEt

V03-17

52,635

71,872

37

0.66

Pi1-K800

V03-41

69,860

98,177

41

0.48

Pi1-LaTr

V03-28

58,601

63,425

8

0.31

Pi1-PEG1

V03-35

59,624

93,104

56

0.38

Pi1-PEG2

V03-32

65,219

94,048

44

0.43

Pi1-PEG3

V03-20

52,700

68,616

30

0.31

Pi1-Sac

V03-45

54,560

61,158

12

0.49

Pi1-Sil

V03-42

54,128

72,204

33

0.90

Sp1-Air

V23-20

45,100

98,004

117

1.48

Sp1-K800

V23-08

60,128

177,153

195

2.49

Sp1-LaTr

V23-02

57,273

206,642

261

3.95

Sp1-PEG1

V23-25

68,803

144,463

110

0.62

Sp1-PEG2

V23-30

68,719

95,985

28

0.44

Sp1-PEG3

V23-28

70,485

107,966

35

0.26

Sp1-Sac

V23-29

56,646

226,761

300

2.78

Rights and permissions

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data.

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Stelzner, J., Stelzner, I., Martinez-Garcia, J. et al. Stabilisation of waterlogged archaeological wood: the application of structured-light 3D scanning and micro computed tomography for analysing dimensional changes. Herit Sci 10, 60 (2022). https://doi.org/10.1186/s40494-022-00686-6

Download citation

  • Received:

  • Accepted:

  • Published:

  • DOI: https://doi.org/10.1186/s40494-022-00686-6

Keywords

  • Conservation
  • Waterlogged archaeological wood
  • Volume
  • Shrinkage
  • Computed tomography
  • Structured-light 3D scanning