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How an integrated diagnostic approach can help in a correct evaluation of thestate of preservation of waterlogged archaeological wooden artefacts

Nicola Macchioni a, Benedetto Pizzo a,*, Chiara Capretti a, Gianna Giachi b

aCNR-IVALSA, Via Madonna del Piano 10, I-50019 Sesto Fiorentino, Italyb Soprintendenza per i Beni Archeologici della Toscana, Largo del Boschetto 3, I-50143 Firenze, Italy

a r t i c l e i n f o

Article history:Received 1 October 2011Received in revised form10 May 2012Accepted 17 May 2012

Keywords:Waterlogged archaeological woodDiagnosisMicromorphologyCell wall chemical componentsPhysical analysisMicroscopic analysis

a b s t r a c t

Artefacts made of wood coming from archaeological excavations provide insights into human culturalbehaviour of the past. They show how man utilised natural resources and how the development ofwoodworking techniques and artistic endeavour were developed. Within archaeological contexts,waterlogged anaerobic conditions generally preserve the appearance of artefacts, although wood issubject to severe decay processes. The said conditions can transform the original material into a new one,thus demonstrating specific differences from those of the “fresh” wood of the same species. In order toassess these new properties correctly, an integrated diagnostic approach is needed, one which includesa multidisciplinary (micromorphological, physical and chemical) evaluation of the state of preservation.

This paper reports several diagnostic results regarding wood artefacts coming from a series ofarchaeological excavations carried out in Italy. Different types of artefacts e ships, furniture, foundationpiles, etc. e that date to different eras (Roman times, the Middle Ages, the Renaissance) have beenincluded in this study. In addition, several species of wood at different levels of decay were analysed. Ourstudy provides evidence of how a multidisciplinary approach, based on anatomical (micromorpholog-ical), physical and chemical analyses, avoids goes beyond the limits of each single type of analysis, thuscontributing to a complete and reliable evaluation of the state of preservation of these archaeologicalartefacts.

� 2012 Elsevier Ltd. All rights reserved.

1. Introduction

Artefacts made of wood and coming from archaeological exca-vations provide insights into human cultural behaviour of the past,and therefore have a declared archaeological value: they testify toman’s utilisation of natural resources as well as to the developmentof woodworking techniques and artistic endeavour. In the event ofa rapid and complete burial in an anaerobic environment (forinstance, under the sediment of the seabed), wood can bepreserved for a very long time. Nevertheless, a certain degree ofdeterioration always occurs even in a water-rich and oxygen-poorenvironment, and produces morphological, physical, and chem-ical modifications (Hoffmann and Jones, 1990). At present, in orderto assess the preservation of wood retrieved from archaeologicalsites, artefacts are first subjected to macroscopic evaluation, whichsometimes also includes a pin test (Florian, 1990). They laterundergo gravimetric measurements in order to calculate the

Maximum Water Content (MWC), which is commonly consideredto be the most important parameter for diagnosing this kind ofmaterial (Schniewind, 1990). In fact, decay induces an increasedporosity in wood cell walls. The filling of these new pores withwater in waterlogged conditions causes an increase in the relativepercentual amount of water in decayed wood, and the MWC cantherefore be considered to be directly proportional to the amount ofdecay. Thus, it gives an indirect evaluation of residual porosity inwaterlogged archaeological wood. However, in addition to theMWC, other types of physical parameters, such as basic density andshrinkage coefficients, provide additional information on the stateof preservation of archaeological wood. Basic density providesa measurement of the residual mass of wood, whereas shrinkagecoefficients give an indication of its loss in terms of orthotropicity.In the decayed wood, both aspects have a connection with eachother: the anisotropy changes because of a decrease in the cellulosemicrofibrils (Grattan and Clarke, 1987), which is due to attacks byfungi and bacteria. As a result, there is a change in the typical ratiobetween shrinkages in longitudinal, radial and tangential direc-tions. This changemainly affects the ratio between longitudinal andradial shrinkages, which, depending on the decay level, can

* Corresponding author. Tel.: þ39 055 522 5623; fax: þ39 055 522 5507.E-mail address: pizzo@ivalsa.cnr.it (B. Pizzo).

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increase to as much as 1:2e1:5, compared to the normal 1:10. Onthe other hand, in most decayed samples the tangential shrinkagecannot be measured, or can be measured only with great difficulty,because the samples frequently tend to collapse.

Instead, micromorphological (MM) analysis, although notalways performed as a routine procedure, represents a directmeans for assessing decay from a qualitative perspective. MMobservations offer multiple possibilities for use, and make itpossible to identify:

1. the taxon constituting the artefact, and thus to compare thecurrent characteristics of the archaeological woodwith those ofsound material of the same species, in an attempt to appraiseits state (Björdal et al., 2000; Capretti, 2008; Klaassen, 2008);

2. the biological agents that caused the decay in the wood(bacteria, fungi);

3. the depth of their penetration into thewoodwith respect to theexternal surface (Björdal et al., 2000; Blanchette et al., 1990).

Lastly, chemical analysis makes it possible to quantitativelyevaluate the wood’s chemical composition. This is usuallyexpressed as a residual amount of holocellulose, lignin, extractives,and ash, and provides important indications regarding the newpeculiar characteristics of waterlogged archaeological wood(Hedges, 1990).

Table 1 contains a representation of the advantages and disad-vantages of using the methodologies described. However, whileonly one or atmost two types of analyses are commonly carried out,a complete multidisciplinary diagnosis of waterlogged archaeo-logical wood is not often encountered in the scientific literature (asfar as we know, only in the paper by Capretti et al., 2008, in whichthe three techniques are used in synergy).

The results presented here indicate that only an integratedapproach to diagnosis permits a reliable and correct evaluation ofthe state of preservation of waterlogged archaeological wood,whereas each type of analysis applied singly can lead toa misleading evaluation.

To illustrate this point, several diagnostic experiments onwooden artefacts coming from archaeological excavations under-taken in Italy (Venice, Comacchio, Pisa, Naples) are described: inthe examples reported here, misleading information related tosingle analyses was revealed when using the integrated approach.

2. Materials and methods

Samples (more than 200) from various Italian excavations havebeen analysed during the years at the CNR-IVALSA laboratories andat those of the “Soprintendenza per i Beni Archeologici dellaToscana”. They involved different types of artefacts (ships, furni-ture, foundation piles, etc.), historical periods (Roman times, theMiddle Ages, and the Renaissance), wood species, and levels ofdecay. In view of the aims of this study, only the most represen-tative are reported here. Their origin and other details pertaining tothe materials are described in specific sections.

2.1. Micromorphological analysis

MM analyses were carried out using transmission opticalmicroscopy (TOM), as well as scanning (SEM) and transmission(TEM) electron microscopy (even if to a lesser extent). Analyseswere performed by means of:

- DMRB Leitz and DMLB2 Leica transmission optical microscope;- XL 20 Philips and Quanta 200 FEI Company scanning electronmicroscopes;

- EMC201, Philips transmission electron microscope.

Each technique required an appropriate preparation of water-logged wood samples: for TOM, thin sections were cut manuallyfrom frozen samples using a razor blade; for SEM, bulk sampleswere dehydrated by exploiting the Critical Point Dryer technique1

and then coated with gold; as for TEM, the wood was firstembedded in Spurr resin and then cut with an ultra-microtome inorder to obtain ultra-thin [<90 nm thick] sections (Bonzi and Luzzi,1981).

In addition to SEM, it is possible that an Environmental ScanningElectron Microscope (ESEM) could also be used successfully forverifying the extent of the decay in waterlogged wood. However,according to our experience, this technique reveals limits indetailed analysis, in that the quality of the images collected ishighly dependent on the degree of dehydration of the wood. In thecases (not reported here) in which both SEM and ESEM techniqueswere used on the same samples, it was evident that the generalappearance of the cell walls was similar. This confirmed that the useof a combination of a Critical Point Dryer and gold coating did notcause any warping or collapsing of cell walls.

2.2. Physical analysis

A physical characterisation of waterlogged archaeological woodwas carried out by measuring the following physical parameters:

1) Maximum Water Content (MWC), which is the most commonmethod for measuring the extent of decay in archaeologicalwood, is given by:

MWC ¼ 100$MWET �MANHYDR

MANHYDR

whereMWET andMANHYDR are the mass of wood inwaterlogged andanhydrous conditions, respectively.

We always made sure that the water content was the realMaximum Water Content by maintaining samples in waterbetween the sampling and the analyses. In our experience, it isdangerous to force more water by vacuum on decayed samples,because collapses inevitably occur;

2) Basic density (Bd), measured by using the ratio between theanhydrous mass and the waterlogged volume (Hoffmann andJones, 1990; Macchioni, 2003; Schniewind, 1990);

3) dimensional movements (longitudinal, tangential and radial b)of wood were also calculated by measuring the dimensionsunder swollen and oven-dried conditions, but only when thesampling allowed for preparing prismatic specimens that werewell oriented along the three anatomical wood directions.Shrinkages were always measured on the same samples uti-lised for measuring Bd, after these had been oven-dried.

The Basic density (Bd) value was used to measure the ResidualBasic density (RBd), which was calculated as the ratio between themeasured density of the archaeological material and the averagedensity for non-degraded wood of the same species, as derivedfrom the literature (Grattan and Clarke, 1987).

1 To avoid any possible dramatic effect on the wood structure, the application ofthis technique was preceded by a succession of baths in always more concentratedmixtures of distilled water and acetone, using pure acetone for the final step. Thesamples were then fixed as suggested in Björdal et al. (1999).

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Table 1Synoptic table of the methods most used to characterise waterlogged archaeological wood, with related advantages and disadvantages. Most of these are based on theexperience gained by the authors. In the Table, ‘n/a’ means ‘not applicable’.

Diagnostic technique Sample size Advantages Disadvantages

Microscopy In general n/a - Identification of taxon- Qualitative evaluation of thedecay through the determinationof the responsible biological agentsand of the depth of their attack

- Limited action of the analysis: areas ofthe order of millimetres and less areobserved

Transmission OpticalMicroscopy (TOM)

Thin sections of�2 mm side

- Easy to perform, it does not requirevery costly instrumentation

- Waterlogged samples need preventivepreparation by freezing or by embeddingthem in resin in order to cut them intothin sections

Scanning ElectronMicroscopy (SEM)

Massive samples of�2 mm side

- High resolution 3D images of thesamples can be collected

- Waterlogged samples need preventivedehydration and coating

- Resolution depends on both the surfacecharacteristics and the samplepreparation

- The instrument is expensive and notalways available

EnvironmentalScanning ElectronMicroscopy (ESEM)

Massive samples of�2 mm side

- 3D images of samples can be collectedwith no need for preventive preparationof the waterlogged samples: dehydrationoccurs inside the instrument.

- No traumatic action on the wood anatomyis expected

- Detailed analysis is less effective thanthat attained through SEM

- Resolution depends on both the surfacecharacteristics and the sample preparation

- The instrument is expensive and notalways available

TransmissionElectronMicroscopy (TEM)

Ultra-thin sections of�1 mm side

- High resolution 2D images of samples canbe collected

- Samples need a complex preliminarypreparation (embedding and ultra-thincutting), which requires a long time

- The instrument is very expensive andnot always available

Physical analysis In general n/a - Quantitative evaluation of the decay bymeans of a comparison with values forsound wood of the same species

- A minimum quantity of material ofapprox. 100 mg is needed to obtainreliable values (gravimetric measurements)

Maximum WaterContent (MWC)

Samples of �100 mgon a wet wood basis

- This is a ‘familiar’, widespread parameterthat is easily understood

- Measurements are easy to carry out withfairly inexpensive equipment

- Measurements can also be performedon site

- Misleading results can be obtained whenthe gravimetric measurements are notreliable (for instance, due to the presenceof mineral inclusions, or in the presenceof collapsed material)a

- Samples have to be at their maximumimbibition state for the measurementsto be correct

Basic density (Bd) Samples of �100 mgon a wet wood basis

- Measurements are easy to carry out withfairly inexpensive equipment

- Misleading results can be obtainedwhen the gravimetric measurementsare not reliable (for instance, due tothe presence of mineral inclusions, or inthe presence of collapsed material)a

Residual Basicdensity (RBd)

n/a - Measurements are easy to carry out withfairly inexpensive equipment

- Measurements are additionally affectedby the imprecision in values used forthe basic density of sound wood, whichmust to be taken from average data inthe literature

Shrinkages (b long.,tang., rad.)

Prismatic samples ofmillimetre scaleoriented along thedirections of the wood

- Measurements make it possible to knowwhether the wood is still anisotropic

- Measurements are not always possibledue to the occurrence of collapse andthe consequent development ofdeformations and cracks

Chemical analysis(gravimetric)

In general n/a - Measurements are easy to carry out withrelatively inexpensive equipment

- Measurements are slow and tedious- Expertise is requested

Residual amountsof lignin (L) andholocellulose (H)

Samples of �250 mgof dry milled wood

- Detailed description of residual chemicalcomposition of wood tissue

- As it is gravimetric, the analysis requireslarge portions of waterlogged material,especially for extremely decayed samples

- Procedures for determining holocelluloseare affected by imprecision, and so thisparameter is better evaluated by difference

Holocellulose,lignin ratio (H/L)

n/a - Although gravimetric, the measurementsare not affected by the ash (mineralinclusions) content

- If errors are present in direct measurements,these errors can also be increased byusing their ratio

Ash Samples of �250 mgof dry milled wood

- Measurements are easy to carry out, withequipment that is not overly expensive

- Volatile compounds formed after a reactionat a high temperature are not assessed

a Outcome of present paper.

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2.3. Chemical analysis

The chemical characterization of the archaeological wood wascarried out by following the international standard methodologiesthat are normally used on fresh wood (TAPPI, 1996-7), with a fewvariations in view of the small amount of material available. Themeasurements were carried out as described previously (Pizzoet al., 2010). In brief, the procedure consisted of a Soxhlet extrac-tion of wood flour, first in organic solvents (a 2:1 v/v mixture ofethanol and toluene) and subsequently in deionised water. After-wards, the lignin was measured according to Klason’s method ona part of the extracted meal, while the remaining part was used fordetermining the holocellulose content using the proceduresdescribed by Norman and Jenkins (as reported in Browning, 1967).All measurements were performed on sieved material (40e60mesh, corresponding to 0.2e0.4 mm). The quantitative resultsrefer to the anhydrous weight of the wood flour, and indicate theamount of the residual chemical components. The decay was thusevaluated by comparing the values of the decayed wood with thoseof fresh wood of the same species. However, it is worth noting thatthe results on fresh material were fairly varied and somewhataffected by the test methods. Therefore, the small differences foundin the lignin and holocellulose content may well be insignificant.

3. Results and discussion

3.1. Cases in which the various approaches gave comparable results

In most cases, each diagnostic approach made possible a cleardiagnosis, and gave results that were in good agreement. Someexamples are given here as follows.

3.1.1. PisaSeveral portions of hull or entire hulls of ancient ships dating

back to the period ranging from the IInd century BC to the Vthcentury AD were discovered at S. Rossore, near Pisa (Giachi et al.,2000, 2006). MM analysis made it possible to identify the woodspecies constituting the hulls and then to make an inventory of thetypes used for their realization, thus enabling a correlation of eachwood type with its structural function. Ship A and Ship F arespecifically considered here. In Ship A (end of the IInd c. e begin-ning of the IIIrd c. AD), the planking was entirely made of Pinuspinaster Aiton (maritime pine), while Quercus spp. (deciduous oak),Ulmus sp. (elm) and Juglans regia L. (walnut) were used for theframes. In all the sample wood, the MM analysis pointed outwidespread attack by soft rot fungi and bacterial erosion (Fig. 1),which caused a severe loss of wood mass, with a consequentincrease in porosity. Microscopic observation also revealed thepresence of very thin erosion channels caused by bacteria, and thatof fungi spores, which were visible in both cross and longitudinalsections.

In particular, TEM analysis revealed the total transformation ofthe S1 and S2 layers due to bacteria and fungi attacks in the oakwood of Ship F. The wall was transformed into a material withoutconsistency, and the cells only partially retained their originalshape (Fig. 2).

In many cases, the results of the physical and chemical analyses(some examples are reported in Table 2 for Ship A) confirmed woodthat was greatly decayed, and characterised by a high MWC (464%on average, with a maximum of 633%), very low Bd (0.14e0.31 g/cm3), and correspondingly low values of RBd (21e46%). Theresults of the chemical analyses are summarised in both theholocellulose/lignin (H/L) ratio and the lignin content. They alsoconfirm averagely the loss of most of the original chemicalstructural components: the actual H/L values were as low as

0.1e0.4. The corresponding values for non-decayed wood arereported in Table 6.

3.1.2. ComacchioIn the neighbourhood of Comacchio, a Roman ship, the so-

called Fortuna maris (Ist c. AD), was excavated in a deltaic envi-ronment (Berti, 1990). The ship’s hull was made of Ulmus sp. (elm).Surprisingly, the micromorphological examination identifieda wood that is very similar to sound “fresh” wood. The cell walls

Fig. 1. Pisa. TOM images of transversal (a) and longitudinal (b, c) sections of Pinuspinaster Aiton from ship A (PA-A2). In the images, the arrows point out: a) fungalspores between the degraded secondary cell wall and the middle lamella; b) chains offungal spore inside the cell lumen; c) typical morphology of an erosion bacteria attackaround the areolate pits (bars 20, 50, 20 mm, respectively).

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seemed not to have suffered any attacks by microorganisms(Fig. 3).

Table 3 shows the results of chemical and physical analyses ofthe sampled wood. With the exception of sample CM-1, the resultsrevealed a state of preservation of waterlogged wood comparableto that of sound wood of the same species: i.e. values measured for

the archaeological material were very similar to the correspondingvalues for non-decayed wood (Table 6). This was particularlyevident for samples CM-2, 5 and 7. In general, the results from allthe diagnostic assays were in good agreement.

3.2. Cases in which only the integrated approach resulted ina correct diagnostic evaluation

In specific cases, some of the diagnostic techniques consideredgave misleading results, thus making necessary an integratedapproach in order to obtain a correct evaluation of the state ofpreservation of the wood. Some examples are given here as follows,together with the reason for the potential error associated witheach technique:

3.2.1. NaplesRecently, three shipwrecks dating back to Roman times were

found at Naples, close to the coast (Capretti et al., 2008). Thediagnostic results on the wood samples of Ship B are reported hereby way of example. The hull was made mainly of Cupressus sem-pervirens L. (cypress), while Picea abies Karst. (spruce), Quercus ilexL. (holly oak), Fagus sylvatica L (beech), J. regia L. (walnut) and Ulmussp. (elm) were found to be used for the frames.

In various samples, a strong biological decay (bacterial erosionand soft rot caused by fungi) was found (see Fig. 4), and often led tothe depletion of the tracheid pitting in softwoods.

Table 4 shows some noticeable contrasts between the resultsfrom the physical evaluations and the H/L ratio values. For instance,samples NB6 and NB9 showed low MWC values (below 200%),while the H/L ratios were among the lowest (0.3 and 0.7, respec-tively), thus evidencing an opposite trend. This discrepancy wasrelated to the high amount of ash, which was representative of theinorganic content within the wood tissue. In particular, sample NB9had an ash content about of 70% (in sound wood, this value is lessthan 1%), and this fact appreciably affected the measurements ofboth the MWC and the Bd, which were based on gravimetricevaluations. On the contrary, the H/L was virtually unaffected bya high ash content, because both the lignin and the holocellulosewere calculated on the basis of the effective wood mass (theamount of ash was excluded from the sample weight).

3.2.2. VeniceThe foundation piles of some historic buildings (XIV-XVII cent.

AD) in Venice were subjected to a diagnostic study in order toinvestigate their state of preservation (Biscontin et al., 2011;Macchioni et al., 2009). The TOM observation highlighted the factthat thewood of Alnus glutinosa (L.) Gaert. (alder), Quercus sp. (oak),and Larix decidua Miller (European larch) trees had been utilized.The decay in the wood appeared to be extensive, mainly on pilesmade of alder, and was mostly due to bacterial erosion. In Fig. 5, thetypical feature due to degradation from erosion bacteria is shown

Table 2Pisa: Results of the chemical and physical characterisations of some selected wood samples from Ship A. In the Table, WAW is the waterlogged archaeological wood, Bd isthe Basic density, MWC is the Maximum Water Content, and H/L is the ratio between Holocellulose and Lignin. b values are shrinkages along the three anatomical directions(L, R, T). Lignin values refer to the weight of the anhydrous sample. One analysis per sample was carried out because of the limited availability of the material. The symbol ‘e’refers to measurements not carried out because of cell collapse.

Sample Wood species Bd of WAW (g cm�3) RBd (%) MWC (%) Lignin (%) H/L of WAW b long. (%) b tang. (%) b rad. (%)

PA-A1 Quercus sp. 0.31 46 261 64 0.1 e e e

PA-A2 Pinus pinaster Aiton 0.18 35 483 51 0.4 4.2 e e

PA-A3 Quercus sp. 0.18 26 506 69 0.1 2.7 0.8 1.2PA-A4 Ulmus sp. 0.17 29 543 59 0.1 1.6 e e

PA-A5 Juglans regia 0.19 31 462 62 0.1 e e e

PA-A6 Quercus sp. 0.14 21 633 51 0.1 1.9 e e

PA-A7 P. pinaster Aiton 0.23 45 362 58 0.3 3.3 e e

Fig. 2. Pisa. TEM images of a transversal section of Quercus wood sampled from Ship F(PA-A3). The biological attack transformed cell wall in a very porous material.Instrumental magnification is 2240� in (a) and 4380� in (b).

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with its characteristic groove-like erosion (Klaassen, 2008). Theresults of chemical and physical analyses on several piles are shownin Table 5 (and are to be compared with the analogous values fornon-decayed wood reported in Table 6). Most of the alder samples(V-L, V-N, V-P) evidenced appreciable decay: the averageMWCwasof the order of 600% with a H/L of 0.6. The anatomical features ofthe representative V-L sample are shown in Fig. 6. However,unusual and misleading conditions were found during the diag-nosis, and an anomalous result was obtained in the case of the V-Msample. From a simple consultation of the physical parameters asreported in Table 5, it can be seen that this samplewas seemingly inbetter conditions than the other alder samples: the MWC was only204%, and the RBd was approximately 90%. In contrast, the chem-ical parameters showed a high level of decay: the value of the H/Lratio was the lowest (0.4), and lignin constituted 70% of the woodtissue (this value was 23% for non-degraded alder), thus signifyingthat most of the polysaccharides had been lost. On the other hand,the amount of ash could not justify the diagnostic differencesbetween the MWC and the H/L, because this amount was only 4%. Itwas possible to explain the said incongruence after the MM anal-ysis, which showed that the V-M sample had collapsed. This factapparently indicated that there was less room for water in thisparticular sample (Fig. 6).

Table 5 also reports the case of sample V-H, which was takenfrom a larch-wood board. This sample showed a very low MWC

value (64%) and a high Bd value (0.91 g/cm3), which correspondedto an anomalous RBd value that was found to be much higher than100%. Chemical analysismade it possible to explainwhy the densityvalues seemed to be so high: the ash contentwas almost 70% in thatsample: i.e. more than 2/3 consisted of inorganic materials, thusovershadowing the real residual density of the sample.

3.2.3. PisaSample PA-A1 (Table 2) was taken from an oak artefact. It

showed a low MWC value (261%) that did not correspond to thevery low H/L (0.1) and RBd (46%) values. The MM observationshowed a partial collapse involving fibres and radial parenchyma,but excluding the large vessel (Fig. 7). In this case, the contrastbetween the values measured in each single analysis was not asapparent as it was in previous cases. Therefore, it shows just howinsidious it can be to place excessive confidence on only one type ofevaluation.

As evidenced by the various examples presented above, collapseand high ash content represent the most common cases of eventualsnags to making a correct evaluation of the state of preservation inwaterlogged wood. In the present work, only 3 representative casesfor ash (samples NB6, NB9 and V-H), and 2 for collapse (V-M andPA-A1) were presented. However, after more than 200 samples hadbeen analysed, we found a total of 17 cases of collapsed wood and26 cases of ash content higher than 10% (9 higher than 15%).

Table 3Comacchio: Results of chemical and physical analyses of the samples obtained from the hull of the “Fortuna maris”. One analysis per sample was carried out because of thelimited availability of the material. For the meaning of the symbols, consult Table 2.

Sample Wood species Bd of WAW (g cm�3) RBd (%) MWC (%) Lignin (%) H/L of WAW b long. (%) b tang. (%) b rad. (%)

CM-1 Ulmus cf. minor 0.13 21.8 751 73 0.1 9.1 69.5 21.7CM-2 0.42 74.3 172 29 1.9 0.4 e e

CM-3 0.23 41.1 359 31 1.7 1.5 e e

CM-4 0.20 35.2 431 35 1.5 4.3 e 20.0CM-5 0.43 74.6 168 31 2.0 1.1 20.0 6.9CM-6 0.17 30.0 518 35 1.5 3.0 e e

CM-7 0.39 68.9 189 32 2.0 �0.5 25.7 13.6

Table 4Naples: Physical and chemical characterizations of the samples from Ship B. One analysis per sample was carried out because of the limited availability of the material. Ligninvalues, extractives and H/L ratio refer to the effective mass of wood (i.e. by excluding ash from the sample weight). For the meaning of the other symbols, consult Table 2.

Sample Wood species Bd of WAW (g cm�3) RBd (%) MWC (%) Lignin (%) H/L of WAW Extractives (%) Ash (%)

NB1 Ulmus sp. 0.40 70.8 189 35 1.4 5.0 54.2NB4 Fagus sylvatica 0.20 32.3 449 76 0.1 8.8 16NB6 Picea abies 0.41 107.1 194 62 0.3 4.4 9.7NB7 Cupressus sempervirens 0.52 99.7 129 37 1.4 4.0 3.4NB8 Cupressus sempervirens 0.31 59.6 258 39 1.2 5.7 2.9NB9 Cupressus sempervirens 0.61 117.1 120 43 0.7 5.8 68.9NB11 Cupressus sempervirens 0.37 70.5 208 36 1.2 5.3 13.7NB12 Cupressus sempervirens 0.39 75.7 204 45 0.4 4.5 6.3NB13 Quercus ilex 0.22 30.4 398 74 0.1 6.0 5.7

Table 5Venice: Physical and chemical results on some foundation piles. One to threereplicates per sample were carried out, depending on the availability of material.Lignin values, extractives and H/L ratio refer to the effective mass of wood (i.e. byexcluding ash from the sample weight). For the meaning of the symbols, consultTable 2.

Sample Woodspecies

Bd of WAW(g cm�3)

RBd(%)

MWC(%)

Lignin(%)

H/L ofWAW

Extractives(%)

Ash(%)

V-H Larixdecidua

0.91 162.5 64 46 1.1 6.1 68.4

V-J Quercus sp. 0.46 69.2 148 32 1.9 7.2 4.1V-L Alnus sp. 0.17 42.3 519 51 0.6 10.2 3.0V-M Alnus sp. 0.36 89.6 204 70 0.4 3.6 4.0V-N Alnus sp. 0.15 37.5 603 65 0.4 9.3 2.9V-P Alnus sp. 0.13 33.1 703 54 0.7 5.9 5.4

Table 6Reference values for non-degraded wood utilized as a comparison for the analogousvalues of the decayed wood. The lignin content and H/L ratiowere measured directlyby using the same methodologies as for the archaeological samples. The Bd valueswere taken from the literature (Giordano, 1981).

Wood species Lignin (%) H/L Bd (g cm�3)

Alnus sp. 23 2.7 0.40Cupressus sempervirens 32 2.0 0.52Fagus sylvatica 20 3.0 0.61Juglans regia 22 2.6 0.61Larix decidua 24 2.2 0.56Picea abies 28 2.0 0.38Pinus pinaster Aiton 26 2.1 0.52Quercus sp. 20 2.4 0.67Ulmus sp. 25 2.1 0.57

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3.3. The importance of a correct diagnostic evaluation

From the data reported here (Tables 2e5), it clearly appears thatwaterlogged archaeological wood is a different (“new”) materialcompared to fresh wood. Polysaccharides (cellulose and hemi-celluloses) were originally 2e3 times more abundant than lignin,while in the most greatly decayed samples the amount of hol-ocellulose was only 1/10 of lignin. In the same samples, the densityof the residual material was 10e20% of the original one.

This fact also reflects on the important technological propertiesof wood, which depend on the extent of the decay that hasoccurred. For instance, as shown, the orthotropicity was appre-ciably reduced (Tables 2 and 3). Moreover, the hygroscopicity alsochanged: Table 7 reports the average EquilibriumMoisture Content

Fig. 3. Comacchio. TOM images of elm wood sampled from the Roman ship: trans-verse (a), tangential (b) and radial (c) sections of sample CM-2. The wood showeda very sound aspect, comparable to that of fresh wood (bars 10 mm).

Fig. 4. Naples. SEM images of cross (a) and tangential (b) sections of a spruce sampleof Ship B (NB6) showing the presence of numerous fungal hyphae in tracheids and rays(bar 20 mm).

Fig. 5. Venice. TOM image of the radial section of a sample of larch taken from the V-Hpile. Groove-like erosion in the cell wall, a typical feature of an attack by erosionbacteria, was evident.

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(EMC) and the physical and chemical characteristics of someadditional waterlogged archaeological wood samples, as comparedto the hygroscopic behaviour of sound wood (Giordano, 1981). Itcan be seen how the EMC values of the decayed wood werecomparable to those of the sound material. However, they shouldhave been different, considering the dramatic depletion of poly-saccharides and the consequent increase in the lignin content

(lignin is generally considered to be much less hygroscopic thanhemicelluloses and cellulose). This result can be explained onlyby hypothesizing that the same decay agents that destroyedhemicelluloses and depolymerised cellulose also attacked thelignin and made it more hygroscopic. This occurrence has also beensuggested in other works in which complex analytical techniqueswere used (Alesiani et al., 2005; Colombini et al., 2009).

Therefore, a correct diagnostic evaluation helps in under-standing the new properties of decayed wood and, in perspective,in classifying the material according to its true level of decay.Currently, archaeological artefacts are always treated after beingdiscovered and prior to being put on display in a museum (Giachiet al., 2010, 2011; Unger et al., 2001). A correct classification ofthis material could make it possible to tailor the treatment methodon the basis of the class of decay. In selected cases, the phaseinvolving impregnation with consolidating substances could evenbe avoided, at least when the normal checks which develop inwood after drying can be tolerated (for instance, when objects donot show colours or woodworking signs on their surfaces).

4. Conclusions

Generally speaking, the MWC is considered to be the mainparameter to be used for diagnostic evaluations on waterloggedarchaeological wood. Instead, this work, which is based on theresults of several diagnostic campaigns carried out on differenttypes of artefacts in different states of preservation, demonstratesthe great importance of an integrated multidisciplinary diagnosticapproach. The various diagnostic techniques considered hereusually give reliable and comparable results in the case of bothwell-preserved and highly-decayed material. However, relevantcases have revealed that single parameters (including MWC)cannot describe the real state of preservation of wood samples, duee for example e to a high ash content or to the presence ofcollapsed cells. Only chemical analysis in the first case (high ashcontent) or anatomical examination in the second (collapse) cancorrect the first evaluationwhich results from the sole use of MWC.Therefore, each type of analysis makes its own contribution to thediagnostic evaluation, whereas single results can be misleading.The final diagnosis comes from connecting up the various analyticalresult in a rational manner, and makes it possible to evaluatecorrectly the effective state of preservation of the archaeologicalmaterial, the properties of which are appreciably different fromthose commonly known for non-degraded wood.

At the same time, a suitable intervention involving the artefactscan be planned only on the basis of a reliable knowledge of thecharacteristics of the material which has to be conserved. Withinthis perspective, a correct evaluation of the MWC is also importantas regards treatment, and a precise classification of the materialdepending on the extent of its decay can be well assessed only bymeans of a synergy of the analysis techniques.

Fig. 6. Venice. TOM images of the transverse sections of alder constituting the V-Lsample (a) in comparison with that of the V-M sample (b) (bar 0.1 mm and 50 mm,respectively).

Fig. 7. Pisa. TOM transverse sections of sample PA-A1 (Table 2), showing a partialcollapse of the fibres and of the radial parenchyma (bar 50 mm).

Table 7Average Equilibrium Moisture Contents (EMC, %) of the archaeological woodsamples at 20 �C and at different RH levels. The physical and chemical characteristicsare also reported. The latter were evaluated on three samples (standard deviation inbrackets).

Wood EMC (%) at different RH (%) Lignin (%) H/L Bd(g cm�3)

35 45 65 85

Elm 8.6 9.3 11.9 16.7 76 (�1.1) 0.1(�0.02)

0.15(�0.01)

Pine 6.9 7.7 10.2 14.9 67 (�6.9) 0.3(�0.09)

0.15(�0.02)

Soundwood

7 9 12 18 See Table 5

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References

Alesiani, M., Proietti, F., Capuani, S., Paci, M., Fioravanti, M., Maraviglia, B., 2005. 13CCPMAS NMR Spectroscopic analysis applied to wood characterization. Appl.Magn. Reson. 29, 177e184.

Berti, F., 1990. Fortuna Maris, la nave romana di Comacchio. Nuova Alfa Editoriale,Bologna.

Biscontin, G., Izzo, F.C., Bini, C., Rinaldi, E., Macchioni, N., Pizzo, B., Capretti, C.,Molon, G., Regini, M., Lionello, A., Cavaggioni, I., Morabito, Z., 2011. Preliminarystudy on the behaviour of the wooden foundations in Venice. In: Campostrini, P.(Ed.), Scientific Research and Safeguarding of Venice, vol. VII, 2007e2010Results. CORILA, Stampa Europrint, Treviso, pp. 57e69.

Björdal, C.G., Nilsson, T., Daniel, G., 1999. Microbial decay of waterlogged archaeo-logical wood found in Sweden. Int. Biodeter. Biodegr. 43, 63e73.

Björdal, C.G., Daniel, G., Nilsson, T., 2000. Depth of burial, an important factor incontrolling bacterial decay of waterlogged archaeological poles. Int. Biodeter.Biodegr. 45, 15e26.

Blanchette, R.A., Nilsson, T., Daniel, G., Abad, A., 1990. Biological degradation ofwood. In: Rowell, R.M., Barbour, R.J. (Eds.), Archaeological Wood. Properties,Chemistry, and Preservation. Advances in Chemistry Series, vol. 225. Am. Chem.Soc., Washington DC, pp. 141e174.

Bonzi, L.M., Luzzi, P., 1981. Ultrastructural modifications of etioplasts, related totheir position in the leaf tissue, in dark-grown seedlings of Salvia splendens L.upon to continuous light. Cariologia 34, 25e52.

Browning, B.L., 1967. Methods of Wood Chemistry, vol. I. Interscience Publishers. ADivision of John Wiley and Sons Inc., New York.

Capretti, C., Macchioni, N., Pizzo, B., Galotta, G., Giachi, G., Giampaola, D., 2008.Characterisation of the waterlogged archaeological wood: the three ships foundin Naples (Italy). Archaeometry 50 (5), 855e876.

Capretti, C., 2008. Proposta di classificazione del degrado nel legno archeologicoimbibito, PhD thesis, Dipartimento di Scienze e Tecnologie Ambientali e Fore-stali (DISTAF), Firenze.

Colombini, M.P., Lucejko, J.J., Modugno, F., Orlandi, M., Tolppa, E.L., Zoia, L., 2009.A multi-analytical study of degradation of lignin in archaeological waterloggedwood. Talanta 80, 61e70.

Florian, M.E., 1990. Scope and history of archaeological wood. In: Rowell, R.M.,Barbour, R.J. (Eds.), Archaeological Wood - Properties, Chemistry, and Preser-vation. Advances in Chemistry Series, vol. 225. American Chemical Society,Washington, DC, pp. 3e34.

Giachi, G., Lazzeri, S., Paci, S., 2000. Il legno utilizzato per la costruzione delleimbarcazioni: indagini preliminary. In: Bruni, S. (Ed.), Le navi antiche di Pisa. Adun anno dall’inizio delle ricerche. Polistampa Ed., Firenze, pp. 80e86.

Giachi, G., Lazzeri, S., Paci, S., 2006. I legni dei manufatti portati alla lucenell’ampliamento sud. In: Bruni, S. (Ed.), Il porto urbano di Pisa antica. Lafase etrusca. II. Il contesto e il relitto ellenistico. Silvana Ed., Milano,pp. 174e178.

Giachi, G., Capretti, C., Macchioni, N., Pizzo, B., Donato, I.D., 2010. A methodologicalapproach in the evaluation of the efficacy of treatments for the dimensionalstabilisation of waterlogged archaeological wood. J. Cult. Herit. 11 (1), 91e101.

Giachi, G., Capretti, C., Macchioni, N., Donato, I.D., Pizzo, B., 2011. New trials in theconsolidation of waterlogged archaeological wood with different acetone-carried products. J. Archaeol. Sci. 38, 2957e2967.

Giordano, G., 1981. Tecnologia del legno. UTET Ed., Torino.Grattan, D.W., Clarke, R.W., 1987. Conservation of waterlogged wood. In: Pearson, C.

(Ed.), Conservation of Marine Archaeological Objects. Butterworth, London,pp. 164e206.

Hedges, J.I., 1990. The chemistry of archaeological wood. In: Rowell, R.M.,Barbour, R.J. (Eds.), Archaeological Wood. Properties, Chemistry, and Preserva-tion. Archaeological Wood. Properties, Chemistry, and Preservation, Advancesin Chemistry Series, vol. 225. Am. Chem. Soc., Washington DC, pp. 111e140.

Hoffmann, P., Jones, M.A., 1990. Structure and the aging process for waterloggedwood archaeological. In: Rowell, R.M., Barbour, R.J. (Eds.), Archaeological Wood.Properties, Chemistry, and Preservation. Advances in Chemistry Series, vol. 225.Am. Chem. Soc., Washington DC, pp. 35e65.

Klaassen, R.K.W.M., 2008. Bacterial decay in wooden foundation piles. Patterns andcauses: a study of historical pile foundations in the Netherlands. Int. Biodeter.Biodegr. 61, 45e60.

Macchioni, N., Pizzo, B., Capretti, C., 2009. Indagini e caratterizzazione del legno. In:Biscontin, G., Izzo, F., Rinaldi, E. (Eds.), Il Sistema Delle Fondazione Ligneea Venezia. Valutazione del comportamento chimico-fisico e microbiologico.Multigraf Spirea Ed., Venezia, pp. 41e59.

Macchioni, N., 2003. Physical characteristics of wood from the excavations ofancient port of Pisa. J. Cult. Herit. 4, 85e89.

Pizzo, B., Giachi, G., Fiorentino, L., 2010. Evaluation of the applicability of conven-tional methods for the chemical characterisation of waterlogged archaeologicalwood. Archaeometry 52, 656e667.

Schniewind, A.P., 1990. Physical and mechanical properties of archaeological wood.In: Rowell, R.M., Barbour, R.J. (Eds.), Archaeological Wood. Properties, Chem-istry, and Preservation. Advances in Chemistry Series, vol. 225. Am. Chem. Soc.,Washington DC, pp. 87e109.

TAPPI, 1996-7. Standards Technical Association of Pulp and Paper Industry. 360Lexington AM, New York.

Unger, A., Schniewind, A.P., Unger, W., 2001. Conservation of Wood Artefacts.Springer Verlag, Berlin.

N. Macchioni et al. / Journal of Archaeological Science 39 (2012) 3255e3263 3263