THE CHARACTERIZATION OF WATERLOGGED ARCHAEOLOGICAL WOOD: THE THREE ROMAN SHIPS FOUND IN NAPLES (ITALY)*

Archaeometry

50

, 5 (2008) 855–876 doi: 10.1111/j.1475-4754.2007.00376.x

*Received 9 November 2006; accepted 18 July 2007†Corresponding author: e-mail: [email protected]© University of Oxford, 2008

Blackwell Publishing LtdOxford, UKARCHArchaeometry0003-813X© University of Oxford, 2008XXX

ORIGINAL ARTICLES

The characterization of waterlogged archaeological woodC. Capretti

et al.

*Received 9 November 2006; accepted 18 July 2007© University of Oxford, 2008

THE CHARACTERIZATION OF WATERLOGGED ARCHAEOLOGICAL WOOD: THE THREE ROMAN SHIPS

FOUND IN NAPLES (ITALY)*

C. CAPRETTI, N. MACCHIONI and B. PIZZO

CNR/IVALSA, Via Madonna del Piano, 10, 50019 Sesto Fiorentino (FI), Italy

G. GALOTTA

Istituto Centrale per il Restauro, Piazza S. Francesco di Paola, 9, 84100 Roma, Italy

G. GIACHI†

Soprintendenza per i Beni Archeologici della Toscana, Laboratorio di Analisi, L.go del Boschetto, 3, 50134 Firenze, Italy

and D. GIAMPAOLA

Soprintendenza per i Beni Archeologici delle Province di Napoli e Caserta, Piazza Museo, 19, 80135 Napoli, Italy

Three apparently well-preserved shipwrecks dating back to Roman times were brought tolight near Piazza Municipio in Naples (Italy), during the excavation for the construction ofLine 1 of the subway. The shipwrecks were covered by marine sand and silt, below the watertable. In order to establish the nature and the extent of wood degradation and, therefore,determine how best to preserve the shipwrecks, a diagnostic investigation was carried out.The study involved the identification of wood species, chemical characterization of theresidue component and physical and micro-morphological characterization.

KEYWORDS:

ARCHAEOLOGICAL WOOD, LIGHT MICROSCOPY, ROMAN SHIPWRECKS, WOOD DEGRADATION, WOOD ANALYSIS, CHEMICAL COMPONENTS OF WOOD, NAPLES

INTRODUCTION

In 2004, excavation work to extend the subway network began in Naples (the capital city ofthe Campania Region, in southern Italy). In order to ensure no damage to cultural heritage,the Soprintendenza per i Beni Archeologici delle Province di Napoli e Caserta preceded theexcavations with an archaeological investigation that delineated the coastal landscape of theancient city of Naples in its articulation and functions. This in turn brought to light severalfindings dating back to Roman times: among them, near Piazza Municipio, were structurespertaining to the ancient shoreline and three apparently well-preserved shipwrecks (Giampaola

et al.

2005b).

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The historical and topographic context

The archaeological investigation clarified that the ancient port of

Neapolis

is today locatedunderneath the centre of Naples. The present Piazza Municipio and Piazza G. Bovio were onceoccupied by the sea, close to the coastline, and were part of a big harbour delimited in the westby the tuff relief of

Castel Nuovo

and in the east by a site that is presently occupied by the churchof S. Maria di Porto Salvo (Fig. 1) (Giampaola

et al.

2004a,b, 2005a,b; Giampaola 2005).Above the Republic-period seabed, a level pertaining to the end of the first century

ad

,containing a pier (23 m long, 4.5 m wide) was discovered. This pier was built perpendicularlyto the coastline, in an east–west direction. Close to it, veering towards the north, twoshipwrecks perpendicular to each other were also found: they have been distinguished by theletters A and C. The ships seem to have been voluntarily sunk and abandoned close to the pier;their hulls were then totally filled by a sand layer that formed during the second century. Later,two additional wooden piers were built and their poles broke the planking of shipwreck A.Shipwreck B, with its lime cargo, sank shortly after and probably shattered on one of the piers.

Shipwrecks A (11.7

×

3.2 m) and B (9.0

×

2.0 m) are so-called

onerariae

, which were shipsused primarily for maritime trade in both small- and medium-scale coastal navigation.Shipwreck C (13.2

×

3.7 m) is a

horeia

, a rarer ship having a plate bottom and a transom bowthat facilitated harbour manoeuvres and was utilized for the loading and unloading of goods,and for fishing. The boats were built according to the planking loading principle, the planksbeing connected through the ‘mortise-and-tenon’ method.

Shipwrecks A and C did not contain any cargo; however, onboard equipment was found,such as fishing and working tools (lines, blocks, needles for fishing nets, wicker baskets,leather shoes and bags). Interestingly enough, however, a lot of almost intact finds thatdemonstrate the complexity of the trades of the prosperous harbour of

Neapolis

were found onthe seabed of the first and second centuries

ad

.

The decay of waterlogged archaeological wood

In the event of a rapid and complete burial in an anaerobic environment (for instance, under thesediment of the seabed), wood can be preserved for a very long time, even if a certain degree ofdeterioration always occurs, producing physical and chemical modifications of wood substances.

In waterlogged contexts, the decay of wood evolves by the loss of the carbohydrate componentswithin the fibrillar texture, from the lumen towards the middle lamella, while the ligninundergoes only some oxidative modification and its content remains almost unchanged(Goldstein 1984; Shiffer 1987; Hedges 1990; Kim 1990; Rowell and Barbour 1990; Fengel1991; Eaton and Hale 1993; Uçar

et al.

1996; Kim and Singh 2000).The degradation of wood is mainly due to the enzymatic processes of biotic agents (fungi

and bacteria), which act before and after it has been embedded. Many studies demonstrate thatdifferent types of degradation and microbial successions take place in buried and waterloggedwood; studies are also bringing to light the importance of bacteria as main degraders, althoughdecay proceeds very slowly. In waterlogged sites with near-anaerobic conditions, erosionbacteria are the only organisms able to degrade wood (Nilsson and Daniel 1988; Blanchette

et al.

1990; Eaton and Hale 1993; Singh

et al.

1994; Björdal

et al.

1999, 2000; Blanchette2000; Powell

et al.

2001). The most important manifestation of erosion decay consists incell distortion, collapse in the tangential direction and the detachment of secondary cell walllayers: the cell lumen is filled with decay products. Cell walls are gradually converted into an

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Figure 1 A plan of the old harbour of Naples.

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amorphous substance consisting of residual wooden material and bacteria, whereas the com-pound middle lamellae, which are richer in lignin, are not so severely damaged, even in themost advanced stages of decay (Blanchette

et al.

1990). Degraded wood shows morphological,chemical and physical alteration and shows poor mechanical properties: therefore, particularcare must be made in drying it, so as not to cause any irreversible damage (Rowell and Barbour1990). The loss of wood substance causes a lower density and a growing microporosity andpermeability: therefore, the wood is bulked by water (Hedges 1990; Fengel 1991). Such woodis often characterized by a high inorganic content due to the deposition of salts and sedimentsinto the fibres (Passialis 1997; Bettazzi

et al.

2005). The degree of decay can be estimated bythe chemical analysis of the residual components (Grattan and Mathias 1986; Pan

et al.

1990;Uçar and Yilgör 1995; Giachi

et al.

2003). Moreover, the measurements of residual densityand of water content in waterlogged wood become an essential parameter to assess the state ofpreservation and to plan the conservation of archaeological waterlogged wood (Schniewind1990; Panter and Spriggs 1997; Passialis 1997; Hoffmann 2003; Jensen and Gregory 2006).

Diagnostic survey and the aim of the work

At the moment of recovery, the three shipwrecks were positioned as shown in Figure 2: thestructure of the hulls was apparently well preserved except for the tops, which were partially

Figure 2 The three shipwrecks brought to light.

https://www.researchgate.net/publication/226239533_Aging_and_fossilization_of_wood_and_its_components?el=1_x_8&enrichId=rgreq-522e4f3c-bd0c-4d77-b609-aa8201c8bd60&enrichSource=Y292ZXJQYWdlOzIyOTc3Mjc0NjtBUzoxMDE3MTc4ODY2MzYwNDlAMTQwMTI2Mjg0MjczNw==


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loose, and the upper edges, which were heavily degraded by

Teredo

bores (Fig. 3). The ship-wrecks were preserved 3.5 m below the present water table (13.5 m below the ground level),embedded in a homogeneous sediment of marine sand and silt. All of the shipwrecks’ woodappeared to be water-saturated and had, in great part, a spongy consistency, especially inthe upper portions of shipwrecks A and C.

A white calcareous deposit, probably due to the transported cargo, partially covered thecentral part of shipwreck B.

1

Moreover, in most of the central planking, calcium carbonatedeposits were present inside the wooden fibres, and the wood had a whitish colour and amineral-like hardness and was particularly hard during sampling. Most of the inner and outerparts of the hulls’ surfaces were covered by a thick layer of waterproofing organic material(most probably vegetable pitch).

Taking into consideration the great historical value of the Roman shipwrecks of Naples, adiagnostic survey was carried out in order to assess the extent of wood degradation by chemical,physical and micro-morphological characterization, and to suggest the most suitable means fortheir conservation. Analytical work was utilized to compare the different approaches normallyused for diagnostic investigations of archaeological wooden findings.

MATERIAL AND METHODS

The samples from the three shipwrecks used for the analyses are listed in Tables 1–3. They wereselected as representative samples of the hulls, and their distribution is shown in Figures 4–6.

1

As resulted from EDX and XRD analyses.

Figure 3 Teredo bore attacks at the upper edge of shipwreck C.

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In the majority of cases, the size of each sample was approximately 4 cm in length, 4 cm inwidth and 3 cm in thickness.

Identification of the wood species and micro-morphological characterization

Identification of wood species

2

and micro-morphological investigations were carried out bymeans of transmission light microscopy (DMRB, Leitz, and DM LB 2, Leica) on thin sectionsof wood (10–20

μ

m), taken in the three diagnostic anatomical directions (transverse, longitudinal-radial and longitudinal-tangential). Different cutting techniques were employed, depending on the

2

The identifications here reported were carried out by IVALSA for diagnostic study. A complete identification of the wood speciesused in the three ships was carried out by the University ‘Federico II’ of Naples.

Table 1 Shipwreck A: the samples collected and their sampling points in the ship’s hull

Sample Sampling point

A1 Planking, table 2, port: T2bA2 Planking, table 1, starboard: T1tA3 Planking, table 3, port: T3bA4 Planking, table 1, port: T1bA5 Floor timber 50, south: M50SA6 Floor timber 50, north: M50NA7 Floor timber 1: M01A8 Futtock 18, starboard: S18tA9 Futtock 18, port: S18bA10 KeelsonA11 Ceiling, table 14a, port: Fi4abA12 Ceiling, table 12a, port: Fi2abA13 Ceiling, table 13b, starboard: Fi3btA14 Ceiling, table 14a, starboard: Fi4atA15 Ceiling, upper table between frames 20/21, port: 20/21

Table 2 Shipwreck B: the samples collected and their sampling point in the ship’s hull


B1 Frame, 06, south: O06SB2 Frame, 14, south, left side: O14SsxB3 Frame, 14, south, right side: O14SdxB4 Frame, 20, north, right side: O20NdxB5 Frame, 20, north, left side: O20NsxB6 Frame, 28, south: O28SB7 Planking, table 2, south: T2SB8 Planking, table 2, north: T2NB9 Planking, table 3, north: T3NB10 Planking, table 4, south: T4SB11 Planking, table 5, south: T5SB12 Planking, table 10, north: T10NB13 Keel


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preservation state of the wood samples. Cubes with a side length of about 0.5 cm were cuteither by hand, using a razor blade on frozen pieces, or by cryomicrotome (Cryostat CM 1900,Leica). Sections for microscopy were cut from the inner part of the samples, in order toinvestigate wood at least 2 cm below the surface.

If necessary, samples were previously embedded in a glycerol-based medium (GlycerolGely, BDH), to improve consistency and elasticity in degraded wood (Fioravanti

et al.

1997).

Table 3 Shipwreck C: the samples collected and their sampling point in the ship’s hull


C1 Futtock 01, starboard, central portion: S01tcenC2 Futtock 01, starboard, external portion: S01testC3 Futtock 01, starboard, external portion: S01testC4 Futtock 035, port, central portion: S035bcenC5 Floor timber 46: M46C6 Ceiling, table 2: Fi2C7 Ceiling, table 3b, starboard, between frames 17/18: Fi3bt17/18C8 Ceiling, table 3b, starboard, between frames 30/31: Fi3bt30/31C9 Ceiling, table 2B: Fi2B17AlC10 Ceiling, table: FiB17DuC11 Ceiling, table: Fi3B45C12 Ceiling, table: Fi4BC13 Planking, table 1, port: T1bC14 Planking, table 9, port: T9bC15 Planking, table 16B, port: T16Bb

Figure 4 The sampling of shipwreck A (the plotting of the hull was realized by Calcagno Architetti Associati s.r.l.and by TecnoIn).

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After cutting, the embedding gel was removed in warm water and the thin sections weremounted on slides. In many cases, sections were stained with a solution of 0.1% w/v anilineblue in 50% lactic acid, in order to highlight micro-organism occurrence. Microbial decay wasinvestigated using both bright-field and polarized light microscopy: the latter is useful todemonstrate the loss of crystalline cellulose.

Identification of wood species was carried out by identification keys and by the comparisonof the collected images with the specialized literature (Greguss 1955; Jacquiot 1955; Jacquiotet al. 1973; Schweingruber 1978, 1990). It was possible to identify almost all of the woodspecies, even if, in a few cases, the identification stopped at genus level because of the heavydeterioration and the collapse of the cells.

Figure 5 The sampling of shipwreck B (the plotting of the hull was realized by Calcagno Architetti Associati s.r.l.and by TecnoIn).

Figure 6 The sampling of shipwreck C (the plotting of the hull was realized by Calcagno Architetti Associati s.r.l.and by TecnoIn).

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Chemical characterization of wood

The chemical characterization of archaeological wood was carried out following the internationalstandard methodologies normally used on fresh wood (TAPPI 1996–7), with some variationsdue to the small amount of available material. It is worth noting that the application of suchprocedures could cause the loss of some structural components of wood. Therefore, frequentlytheir overall amount, expressed in relative terms and referred to the oven-dry material, doesnot reach 100% (Rowell and Barbour 1990; Pizzo et al. 2006).

The methodologies utilized for the analyses of wooden samples are described in Table 4. Allthe measurements have been performed on the sieved material (in the range 40–60 mesh,corresponding to 0.2–0.4 mm). The quantitative results refer to the anhydrous weight of thewood flour and give the amount of the residual chemical components. The decay is thereforeevaluated by comparing the values of the degraded wood with those of the fresh wood of thesame species, as reported in Table 5.

Physical characterization of wood

A small prismatic specimen was obtained from each collected sample, by following theanatomical directions and obtaining as much material as possible from each sample. In general,

Table 4 The methodologies used for the chemical characterization of the archaeological samples

Chemical component Methodology utilized

Organic extracts Soxhlet extraction using a toluene/ethanol mixture, 2:1 v/v (TAPPI T204 modified)Water extracts Soxhlet extraction on the same powder already extracted with the organic solventsLignin content Klason (or acid) method (TAPPI T222), on a part of the extracted meal

(approximately 1 g per sample)Amount of holocellulose Method of Norman and Jenkins as described in Browning (1967),

on the residual part of the extracted meal (approximately 1 g per sample)Ashes Maintenance of the powder in air at 600°C (TAPPI T211)

Table 5 Reference values for fresh wood, utilized for the comparison of the chemical and physical values of thedecayed wood. The H/L ratios have been measured directly by using the same methodologies utilized for the archaeo-

logical samples. The Db values are taken from the literature (Giordano 1981)

Wood species Holocellulose/Lignin (H/L) Basic density (Db)

Cupressus sempervirens 2.0 0.52Fagus sylvatica 3.0 0.61Juglans regia 2.6 0.61Larix decidua 2.2 0.56Picea abies 2.0 0.38Pinus sp. 2.0 0.52Quercus sp. 2.1 0.67Ulmus sp. 2.1 0.57

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the specimens were 2–3 cm in the longitudinal direction and 1–2 cm in the radial and tangentialdirections. The weight and volume (by the water displacement method) of the specimens weremeasured at saturated state and once again after a gradual drying, which was obtained first ina controlled environment (20°C and 65% R.H.) and then in an oven at 103 ± 2°C. The differenceof the values obtained before and after drying allowed us to calculate the most important physicalparameters for evaluating the decay of waterlogged wood (Table 6). The initial characteristicsof the specimen and the impressive deformations during drying permitted calculation of thetotal shrinkages only on a few samples (Macchioni 2003).

RESULTS AND DISCUSSION

The results of identification of the wood species together with those of the chemical and physicalcharacterization of the wood of the three shipwrecks are reported in Tables 7–9.

Wood species

In the three shipwrecks, most of the collected samples are conifers: Cupressus sempervirensL. (Mediterranean cypress), Larix decidua Miller (European larch), Pinus pinaster Aiton(cluster pine), Pinus pinea L. (stone pine) and Picea abies Karsten (Norway spruce).

Hardwoods such as Fagus sylvatica L. (common beech), Juglans regia L. (common walnut),Quercus caducifolia (oak), Ulmus sp. (elm) and Quercus ilex L. (holly oak) were also utilized forthe ships’ construction.

The 15 samples collected for shipwreck C show the most homogeneous composition: nineare of Quercus caducifolia, and three respectively of Pinus pinaster and Picea abies. Cupressuswas utilized mainly for the construction of shipwreck B (6 out of 13 samples).

Results of chemical and physical analyses: comparison among the shipwrecks’ hulls

A preliminary macroscopic observation of wood fragments revealed that in most cases thewood structure was particularly weak even under light pressure. In some cases, differences in

Table 6 The methodologies used for the physical characterization of the archaeological samples

Physical parameter Methodology utilized

Saturated density, SD (g cm−3) Mf/Vf Basic density, Db (g cm−3) M0/Vf Maximum water content, MWC (%) (Mf – M0)/M0 Equilibrium moisture content, EMC (%) Moisture content of samples maintained at 20°C and 65% R.H.Residual density, RDb (%) Dbd/Db

Key to symbols

Mf is the mass at maximum water content.

Vf is the volume at maximum water content.

M0 is the anhydrous mass.

Dbd is the basic density of decayed wood.

Db is the basic density of non-decayed wood.

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Table 7 Shipwreck A: the results of chemical and physical characterization

Sample Species SD Db MWC% EMC% RDb% ls% ts% rs% O.E. (%) W.E. (%) A (%) L (%) H (%) H/L

A 1 Pinus pinea 1.121 0.331 238 13.5 64.9 11.5 1.2 1.6 48.8 25.1 0.5A 2 Larix decidua 1.098 0.281 291 14.1 73.8 0.8 3.4 1.2 2.2 53.7 21.3 0.4A 3 Picea abies 1.087 0.248 339 14.5 65.2 1.9 1.0 4.6 64.8 11.6 0.2A 4 Picea abies 1.090 0.227 379 13.3 59.9 0.05 2.0 1.2 3.3 61.2 19.0 0.3A 5 Juglans regia 1.046 0.131 699 16.3 21.5 2.8 2.0 14.3 68.4 3.9 0.1A 6 Juglans regia 1.040 0.134 678 15.0 21.9 17.0A 7 Ulmus sp. 1.114 0.322 246 15.8 56.5 2.5 1.1 14.5 54.1 24.3 0.4A 8 Juglans regia 1.065 0.167 536 15.7 27.4 2.4 2.9 6.6 76.5 6.0 0.1A 9 Juglans regia 1.059 0.187 468 14.9 30.6 9.4 59.1 25.4 4.0 1.1 4.5 71.3 12.2 0.2A 10 Quercus caducifolia 1.079 0.243 343 15.5 36.3 4.5 2.3 5.0 71.8 7.9 0.1A 11 Picea abies 1.071 0.209 413 14.7 54.9 3.1 2.2 4.3 64.5 11.3 0.2A 12 Cupressus sempervirens 1.119 0.347 222 14.0 66.7 0.2 9.3 2.9 3.1 1.5 1.6 39.6 53.9 1.4A 13 Larix decidua 1.081 0.229 372 14.5 40.9 11.9 8.3 1.2 0.5 1.2 40.2 30.0 0.7A 14 Pinus pinea 1.069 0.228 368 15.2 44.7 1.2 1.1 6.1 64.1 8.0 0.1A 15 Pinus sp. 1.083 0.265 309 12.7 57.5 6.4 1.2 3.0 49.5 20.4 0.4

Key to symbols

SD is the saturated density (g cm−3) of the wood, given by the ratio of the saturated mass and the swollen volume at maximum water content.

Db is the basic density (g cm−3) of the wood, given by the ratio of the anhydrous mass and the swollen volume at maximum water content.

MWC% is the maximum water content of the wood, given by the water mass as a percentage of the anhydrous mass of the wood.

EMC% is the equilibrium moisture content of the wood at constant mass at 20°C and 65% R.H.

RDb% is the residual basic density of the wood, calculated as the density of the sample as a percentage of the basic density of the same wood from the literature.

ls%, ts% and rs% are the longitudinal, tangential and radial shrinkages, as percentages, of the wood samples from MWC to the anhydrous state.

O.E. is the organic extractives (%).

W.E. is the water extractives (%).

A is the ash content (%).

L is the lignin content (%).

H is the holocellulose content (%).

H/L is the ratio between residual holocellulose and lignin.

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Table 8 Shipwreck B: the results of chemical and physical characterization (symbols as in Table 7)

Table 9 Shipwreck C: the results of chemical and physical characterization (symbols as in Table 7)


B 1 Ulmus spp. 1.166 0.404 189 10.7 70.8 1.2 1.1 54.2 16.4 23.7 1.4B 2 Juglans regia 1.065 0.181 488 17.9 29.7 20.2B 3 Juglans regia 1.053 0.158 566 13.7 25.9B 4 Fagus sylvatica 1.082 0.197 449 16.2 32.3 4.7 2.7 16.0 69.0 5.0 0.1B 5 Fagus sylvatica 1.076 0.201 436 13.9 32.9 8.2 1.4 44.4 35.1 18.0 0.5B 6 Picea abies 1.196 0.407 194 7.6 107.1 2.9 23.2 11.9 1.8 2.2 9.7 57.9 15.7 0.3B 7 Cupressus sempervirens 1.186 0.518 129 13.7 99.7 5.9 7.3 3.3 0.6 3.4 37.1 52.0 1.4B 8 Cupressus sempervirens 1.111 0.310 258 13.9 59.6 1.5 11.8 9.2 5.1 0.4 2.9 40.3 47.0 1.2B 9 Cupressus sempervirens 1.339 0.609 120 5.5 117.1 1.4 0.4 68.9 13.8 15.3 1.1B 10 Cupressus sempervirens 1.179 0.450 162 11.5 86.6 2.2 0.6 4.2 36.2 28.4 0.8B 11 Cupressus sempervirens 1.128 0.366 208 14.0 70.5 3.6 1.0 13.7 32.9 41.0 1.2B 12 Cupressus sempervirens 1.197 0.394 204 11.8 75.7 2.9 1.3 6.3 44.0 16.0 0.4B 13 Quercus ilex 1.088 0.219 398 17.2 30.4 2.1 3.6 5.7 73.7 6.9 0.1


C 1 Quercus caducifolia 1.116 0.245 355 15.1 36.6 8.4 9.0 2.3 6.9 64.0 11.9 0.2C 2 Quercus caducifolia 1.130 0.248 354 14.4 37.0 14.3 5.6 4.5 11.3 59.2 5.8 0.1C 3 Quercus caducifolia 1.001 0.222 350 16.0 33.1C 4 Quercus caducifolia 1.084 0.237 356 13.1 35.4 20.8C 5 Quercus caducifolia 1.050 0.165 535 14.6 24.6 18.2C 6 Quercus caducifolia 1.093 0.254 330 14.8 37.9 4.2 1.2 5.5 71.6 6.9 0.1C 7 Pinus pinaster 1.073 0.270 266 15.3 51.9 8.7 13.3 5.3 4.2 5.5 4.3 53.1 26.3 0.5C 8 Pinus pinaster 1.066 0.183 481 14.7 35.2 15.2C 9 Quercus caducifolia 1.068 0.198 439 14.8 29.6C 10 Quercus caducifolia 1.091 0.273 300 14.1 40.7 18.1C 11 Pinus pinaster 1.068 0.183 483 15.2 35.2 17.9 50.0 2.2 0.5 3.9 74.9 6.7 0.1C 12 Picea abies 1.078 0.220 392 14.6 57.9 62.1C 13 Picea abies 1.130 0.240 372 13.6 63.2 56.3C 14 Picea abies 1.025 0.260 293 14.8 68.4 1.5 0.5 8.5 64.0 11.5 0.2C 15 Quercus caducifolia 1.049 0.316 231 13.3 47.2 3.6 27.8 21.1 5.2 0.7 2.5 59.2 27.4 0.5



apparent hardness and strength could be detected in the same element: wood appeared soft andspongy in the outer parts, and relatively fibrous, compact and resistant in the inner parts. Thechemical and physical analyses revealed heavy decay for most of the samples: the holocellulosevalues are low, whereas the amount of lignin is often very high, up to 76.5%. Nevertheless, insome cases this trend is irregular: in shipwreck B, some samples show a lignin content similarto that of holocellulose and in two samples (B4 and B13) the latter is approximately 70% ormore. Moreover, the samples from shipwreck B exhibit a very high ash content (68.9% in B9):this is due to an anomalous penetration of calcium carbonate into the wood fibres coveringmost of the hull at the moment of the discovery.

High levels of decay are also shown by the physical characterization. For example, MWC%values indicate a very high water content, especially in most of the samples from shipwrecksC (up to 535) and A (up to 699), whereas in shipwreck B, MWC% ranges from 120 to 204 in7 out of the 13 samples. It is, however, possible to evaluate the wood decay more effectivelyby using the holocellulose/lignin (H/L) ratio: this parameter allows a direct comparisonbetween the values obtained from the degraded samples and those of the fresh wood. TheH/L ratios are generally less than 0.5 in all the Neapolitan woods, thus indicating a generallyhigh level of decay. Exceptions are represented by samples A12 and A13 from shipwreck Aand by six of those from shipwreck B, whose values are shown in Figure 7.

The loss of holocellulose, with the characteristic orientation of cellulose’s micro-fibrils intothe S2 layer of the cell wall, causes a decrease in the anisotropic characteristics of thedegraded wood (Macchioni 2003). The measured values of the longitudinal shrinkage are veryhigh in the more heavily degraded samples: for instance, 17.0% in A6, 20.2% in B2 and 18.2% inC5, as against values that are commonly less than 1% in non-degraded wood (Giordano 1981).

Concerning the homogeneity of the decay across the three shipwrecks, physical andchemical characterizations demonstrate that a considerable part of shipwreck B is in relativelygood condition, whereas shipwrecks A and C show a greater level of decay (chemical analysesshow on average a higher level of degradation for shipwreck C, but the number of samples wasless in this case). However, the decay is more uniform among the samples from shipwreck C.This is shown, for example, by the values of MWC%: the mean is 369 (± 85) in shipwreck C,whereas it is 393 (± 146) in shipwreck A and 292 (± 153) in shipwreck B.

Figure 7 The holocellulose/lignin ratios for the samples from shipwreck B.



Results of chemical and physical analyses: comparison among the wood species

Cypress, which is largely present in shipwreck B, shows the best state of preservation amongthe woods found in this excavation, as demonstrated by its good chemical and physicalparameters: excluding the anomalous values, average H/L = 1.2, average MWC% = 186 andaverage RDb% = 76.5. Additionally, chemical analysis shows a lignin value quite close to thatof fresh wood (Fig. 8) in all samples except for B9, because of the elevated amount of ashes,which lowers other relative values. Pine and larch give rather uneven results: whereas somesamples show an intermediate decay (A1, A15 and C7: H/L = 0.5 av., MWC% = 238–309 andRDb% = 58.1 av.) others are more heavily decayed (A14 and C11: H/L ~ 0.1, MWC% = 368–483 and RDb% = 39.9 av.). Norway spruce samples are found all over the three shipwrecks:they show a rather uniform, moderately high, level of decay (with H/L ratios in the range of0.2–0.3), even if, in sample B6, the chemical and physical parameters do not show the sameresult.

Despite the few samples available, there are many differences in the behaviour ofhardwoods. Whereas elm samples (A7 and B1) are in a rather good state of preservation(H/L = 0.9 av., MWC% = 189–246 and RDb% = 63.7 av.), oak, holly oak, beech and walnutare more heavily degraded, with H/L values ranging from 0.1 to 0.2, MWC% from 293 to 699and a mean value for RDb% of roughly 30.

Evaluating all of the analyses, the decay seems to be related to the wood species, and in thiscase it seems that softwoods are less decayed than hardwoods.

Based on the reported values, it is also possible to compare the different diagnosticapproaches utilized for the analyses. For this purpose, it is essential to classify the level of thedecay of single samples: for the physical characterization, this was carried out by using theapproach proposed by De Jong (as reported in Grattan and Clarke 1987), with a slightlymodified value, whereas an arbitrary assessment was used for the chemical characterization. Inparticular, a MWC% value of 225, instead of 185 (as proposed by De Jong), was selected toseparate the first class (low decay) from the second one (medium decay), whereas the value of400 was chosen between the medium and high levels of decay. Correspondingly, arbitrary valuesof 0.7 and 0.1 for the H/L ratio were selected to differentiate the three classes of decay.

Table 10 shows the result of this comparison. In a consistent part of the samples, (approximately70% of the total), the two criteria allow for a unique classification. Almost all the species are

Figure 8 The relative amounts of the chemical constituents of wood for the cypress samples from shipwrecks A and B.



graded into the same class, and in particular all of the six pine samples and five out of theseven cypress samples are classified in the same manner. In the other cases (almost 30% ofthe total), the two criteria are very close and the difference between them is only one gradingclass. These differences can be related to several factors: the selection of the limits betweenthe classes; the differing amounts of ashes among samples, which influences the measurementsbased on weight (mainly the physical ones); and the fact that analyses were carried out ondiffering amounts of material—small for physical assessments and relatively large (a fewgrams) for the chemical ones—and thus the latter represents a larger part of the wood.

Decay typologies

The micro-morphological characterization of the wood allowed for an evaluation of the extentof biodegradation and an identification of the main decay pattern of the three shipwrecks.

Microscopic observations demonstrated that bacterial attacks, particularly by erosion bacteria,are mainly responsible for depleting the wood (Fig. 9). The wood showed the non-homogeneousdistribution of the attack: sound cells3 were close to cells whose secondary wall wastransformed into a porous, granular material and which had lost their normal shape and consist-ency. Erosion bacteria, which are the most common type in waterlogged archaeological wood,feed on carbohydrates in the S2 layer, while the compound middle lamellae and S1 layer arestill intact in the degraded cells.

3 Polarized light microscopy showed the intact structure of these cell walls, which appeared bright due to the birefringent natureof the cellulose.

Table 10 A comparison of the results of the different analyses for samples from shipwrecks A, B and C: the gradingclasses were selected as described in the text

Grading Grading Grading

Sample Physical Chemical Sample Physical Chemical Sample Physical Chemical

A1 ** ** B1 * * C1 ** **A2 ** ** B2 *** – C2 ** ***A3 ** ** B3 *** – C3 ** –A4 ** ** B4 *** *** C4 ** –A5 *** *** B5 *** ** C5 *** –A6 *** – B6 * ** C6 ** ***A7 ** ** B7 * * C7 ** **A8 *** *** B8 ** * C8 *** –A9 *** ** B9 * * C9 *** –A10 ** ** B10 * * C10 ** –A11 *** ** B11 * * C11 *** ***A12 * * B12 * ** C12 ** –A13 ** * B13 ** *** C13 ** –A14 ** ** C14 ** **A15 ** ** C15 ** **



Figure 9 LM photographs of transverse sections of softwood samples, showing the characteristic decay pattern caused by erosion bacteria at different degradation levels. (a) Initial and non-homogeneous decay, with apparently undecayed tracheids in latewood adjacent to decayed clusters (Larix decidua, sample A13); (b)–(e) Advanced decay stages, in which the entire secondary cell wall is decayed and tends to disconnect. The typical chequered pattern shows sound tracheids isolated among heavily degraded cells, consisting of amorphous residual material; polarized light (c, e) revealed the high birefringence of the cellulose in the apparently sound cell walls; (b), (c) Cupressus sempervirens (sample B12); (d), (e) Pinus sp. cfr. P. nigra, P. sylvestris (sample A15). Bars: (a) 20 μm; (b), (c) 10 μm; (d), (e) 100 μm.



Besides the biological decay that had developed during centuries of burial, evidence of arecent microbial colonization, due to soil and air contamination, was present.4 This presenceexpanded down to 2–3 cm in depth from the surface, where fungal mycelia had developed(Fig. 10), in addition to a network of very thin hyphae (0.45 μm maximum diameter). Thelatter can be attributed to prokaryote organisms that, according to the microbiological analysis(see note 4), are ascribed to actinomycetes (Fig. 11) (Schaal and Pulverer 1981).

In addition, some soft rot decay was frequently observed, with typical holes within the S2layers of cell walls and cavities with conical ends (Fig. 12).

Finally, it should be pointed out that the tracheid pitting of softwoods was frequentlydetached, in addition to which there was cross-field pitting: in various samples from shipwreck B,it was destroyed to the point of being unrecognizable. In cases where a high level of decaywas present, the multiple effects of different typologies of attack were scarcely distinguishablefrom one another.

CONCLUSIONS

Three Roman shipwrecks were brought to light near Piazza Municipio, during the excavationfor the construction of Line 1 of the subway in Naples. Considering the great historicalvalue of these artefacts, it soon became an obvious necessity to implement a comprehensivediagnostic plan in order to establish the typology and the extent of the degradation of the

4 In agreement with the microbiological analysis carried out a few weeks after the beginning of the excavation, during the recoveryof the shipwrecks. The identification of micro-organisms isolated in culture medium demonstrated an active colonization on woodsurfaces by cellulosolytic fungi (Alternaria sp., Aspergillus niger and Trichoderma viride) and bacteria (mainly filamentous bacteriabelonging to the Actinomycetales order) (Giampaola et al. 2005b).

Figure 10 LM photograph of a tangential section of Picea abies (sample B6), showing the presence of numerousfungal hyphae in tracheids and rays. Bar: 10 μm.



wood, and its future conservation. An investigation was carried out, after the identification ofthe wood species, by means of chemical, physical and micro-morphological characterizations.

Individual analyses

The single analyses showed some interesting results: the greater part of the decay process wasdue to the action of erosion bacteria, which were present in most of the analysed samples.Moreover, some evidence of incipient microbial colonization, by both fungi and filamentousbacteria, was found: they are clearly referable to recent attacks due to soil and air contamination.An appreciable loss of polysaccharides in most of the samples, with the subsequent replacementof the wood substance in the cell walls by water, is a direct consequence of the biologicaldecay. At a macroscopic level, this mechanism is responsible for the spongy consistencyobserved in most of the wood in the Neapolitan shipwrecks.

Nevertheless, in some cases this trend was not confirmed: for example, certain samples fromshipwreck B and some from shipwreck A were in a good state of preservation. In particular, itwas noted that the decay was related to the wood species, with the general rule that softwoodshave less tendency to decay than hardwoods. From this point of view, the example of cypressis very interesting: almost all of the analysed samples can be considered to be in a very goodstate of preservation, still maintaining an elevated residual amount of holocellulose.

Comparison among the analyses

The great diagnostic effort employed in this case allows comparison of the various approaches(micro-morphological, physical and chemical) that are generally used separately for diagnostic

Figure 11 LM photographs of longitudinal sections of Larix decidua (sample A2), showing a network of thin strands,highlighted by staining with aniline blue and lactic acid. The tiny diameter of the filaments (less than 0.45 μm) is referableto prokaryote organisms, specifically actinomycetes. A network of very thin cavities is also visible. Bar: 10 μm.



investigations of archaeological wooden findings. One must consider, however, that theanalyses were carried out on a different scale: very reduced for the micro-morphologicalexaminations (punctual observations on a qualitative basis), and extensive for the physical andthe chemical ones, which provide quantitative results.

From this perspective, the following points can be made:• The convergence of the results coming from the differing diagnostic methods utilized on most

of the samples attests to the adequacy of the single methods of analysis, but at the same timeshows that several approaches are necessary in order to provide a unique and reliable evaluationof the state of preservation of a sample, whereas single measurements can suffer from sizeeffects, or from the distribution of the decay along the finding or across the wooden samples.

• A flexible approach is necessary for a consistent classification of archaeological samples.Giving single value limits in the decay class is only partially useful, while an interval ofvalues might give a better representation. Moreover, an integrated approach, making use ofthe results from the various characterizations, provides for a more adequate grading of thefindings. For this purpose, the physical and chemical investigations are particularly suitablewhen giving numerical values.

• Microscopic observations are essential tools to individualize the decay agents and typologies.Nevertheless, their contribution to the quantitative diagnostic evaluation of woodenarchaeological findings, together with physical and chemical analyses, could be significantly

Figure 12 LM photographs of sections of Picea abies (sample C14), showing the typical appearance of soft rotdegradation. In the transverse section (a), there are small cavities within the S2 layer of tracheid cell wall (arrows),referable to an initial stage of soft rot decay. In the longitudinal section (b), many cavities are visible with conicalends produced by hyphae growing parallel to the cellulose microfibrils within wood cell walls (Blanchette 1990;Eaton and Hale 1993). Bars: (a) 10 μm; (b) 20 μm.



increased by carrying out more comprehensive sampling of the material and, therefore,reducing the problems caused by the different scales of observation.

Suggestions for conservation

As for conservation, the analyses demonstrated that shipwrecks A and C are in an homogeneousstate of preservation, in each case, with samples having a medium or high level of decay, apartfrom a few exceptions.

Considering that neither shipwreck was dismantled when removed, and that they weresuccessively preserved in their lying positions, the same type of treatment can be utilized forall the different wood of both structures, and this choice can be justified because of theirhomogeneous state of preservation. Regarding shipwreck B, a certain distribution of decaywas observed, with some samples being in very good condition (e.g., cypress) and othersheavily degraded. However, one must take into account that the shipwreck was disassembledbefore its removal, and therefore different treatments on the various types of wood will haveto be utilized to facilitate restoration. In the case of the cypress wood, which presented itselfin very good condition, a controlled environment to dry it could be taken into consideration,without the introduction of consolidating products. Nevertheless, considering that the cypresselements have the largest size in shipwreck B, a more accurate and specific investigation isrequired before any definite suggestions for treatment are given.

ACKNOWLEDGEMENTS

The authors wish to thank all the people who collaborated in the positive outcome of thisarchaeological excavation and the subsequent study and, in particular, the Superintendentswho followed one another during the excavation in Naples: Dr S. De Caro, Dr L. Nava, DrV. Sampaolo and Dr F. Zevi. Particular thanks are offered to Dr Giulia Boetto and Dr VittoriaCarsana for their help during the sampling operations and, moreover, to Luigi Fiorentino forthe execution of the chemical analyses.

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THE CHARACTERIZATION OF WATERLOGGED ARCHAEOLOGICAL WOOD: THE THREE ROMAN SHIPS FOUND IN NAPLES (ITALY)*