G.I.S. for the protection and management of Cultural Heritage; and (6) Signiicance,
This volume publishes a total of seventy-two contributions which relect some of application of different scientiic approaches to the common goal of the conservation
Science, Technology
and
Cultural Heritage
editor: M.A. Rogerio-Candelera
SCIENCE, TECHNOLOGY AND CULTURAL HERITAGE
PROCEEDINGS OF THE SECOND INTERNATIONAL CONGRESS ON SCIENCE AND TECHNOLOGY FOR THE CONSERVATION OF CULTURAL HERITAGE, SEVILLA, SPAIN, 24–27 JUNE 2014
Science, Technology and Cultural Heritage
Editor Miguel Ángel Rogerio-Candelera Instituto de Recursos Naturales y Agrobiología de Sevilla (IRNAS-CSIC), Seville, Spain
CRC Press/Balkema is an imprint of the Taylor & Francis Group, an informa business © 2014 Taylor & Francis Group, London, UK Typeset by V Publishing Solutions Pvt Ltd., Chennai, India Printed and bound in Great Britain by CPI Group (UK) Ltd, Croydon, CR0 4YY All rights reserved. No part of this publication or the information contained herein may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, by photocopying, recording or otherwise, without written prior permission from the publisher. Although all care is taken to ensure integrity and the quality of this publication and the information herein, no responsibility is assumed by the publishers nor the author for any damage to the property or persons as a result of operation or use of this publication and/or the information contained herein. Published by: CRC Press/Balkema P.O. Box 11320, 2301 EH Leiden, The Netherlands e-mail:
[email protected] www.crcpress.com – www.taylorandfrancis.com ISBN: 978-1-138-02744-2 (Hbk) ISBN: 978-1-315-71242-0 (eBook PDF)
Science, Technology and Cultural Heritage – Rogerio-Candelera (Ed) © 2014 Taylor & Francis Group, London, ISBN 978-1-138-02744-2
Table of contents
Science, Technology, and Cultural Heritage: An inexorable relationship M.A. Rogerio-Candelera
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Climate change, sea level rise and impact on monuments in Venice D. Camuffo, C. Bertolin & P. Schenal
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Air pollution and preventive conservation in some European museums R. Van Grieken Low cost strategies for the environmental monitoring of Cultural Heritage: Preliminary data from the crypt of St. Francesco d’Assisi, Irsina (Basilicata, Southern Italy) M. Sileo, M. Biscione, F.T. Gizzi, N. Masini & M.I. Martinez-Garrido Monitoring moisture distribution on stone and masonry walls M.I. Martinez-Garrido, M. Gomez-Heras, R. Fort & M.J. Varas-Muriel Effects of open shelters on limestone decay: The case-study of the Bishop’s Palace archaeological site in Witney (England) C. Cabello Briones Air quality assessment and protection treatments impact on the collection of the Museo Naval (Madrid, Spain) J. Peña-Poza, F. Agua, J.F. Conde, P. De San Pío, S. García Ramírez, J.M. Gálvez Farfán, J.M. Moreno Martín, M. González Rodrigo, M. García-Heras & M.A. Villegas Establishing the relationship between underwater cultural heritage deterioration and marine environmental factors. A comparative analysis of the Bucentaure and Fougueux sites T. Fernández-Montblanc, M. Bethencourt, A. Izquierdo & M.M. González-Duarte Natural gamma radioactivity in granites with different weathering degrees: A case study in Braga (NW Portugal) M. Lima, C. Alves & J. Sanjurjo
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27 35
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Accelerated weathering test as environmental behaviour trials on metals M.A. Gómez-Morón, F. Martín-Cobos & P. Ortiz
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Painting woods vulnerability to ultraviolet exposure M.A. Gómez-Morón, A. Tirado & P. Ortiz
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Physical characterization of super-fragile materials in underwater archaeological sites L.C. Zambrano, M. Bethencourt & M.L.A. Gil
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Underwater Cultural Heritage risk assessment related to mean and extreme storm events: A modelling case study in the Bay of Cadiz T. Fernández-Montblanc, A. Izquierdo & M. Bethencourt
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Another source of soluble salts in urban environments due to recent social behaviour pattern in historical centres B. Cámara, M. Álvarez de Buergo, R. Fort, C. Ascaso, A. de los Ríos & M. Gomez-Heras
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Science, Technology and Cultural Heritage – Rogelio Candelera (Ed) © 2014 Taylor & Francis Group, London, ISBN 978‐1‐138‐02744‐2
Establishing the relationship between underwater cultural heritage deterioration and marine environmental factors. A comparative analysis in Bucentaure and Fougueux sites. T. Fernández-Montblanc, M. Bethencourt, A. Izquierdo, M.M. González-Duarte University of Cadiz, Marine Science and Technological Center of Andalusia, International Campus of Excellence of the Sea (CEI•MAR), Puerto Real, Cádiz, Spain
ABSTRACT: In the present work, the relationship between underwater cultural heritage (UCH) deterioration and marine environmental factors assessed in Fougueux and Bucentaure site are presented. The two war ships were sunken during the Trafalgar Battle (1805) in the Bay of Cadiz. An assessment of UCH deterioration was carried out. Firstly, an archaeometry study was conducted by in situ measurement in guns and anchors located in both studies sites. Secondly, corrosion rates in modern samples of different metallic materials (iron, iron cast, copper and brass) placed in both sites were periodically evaluated by mass loss and electrochemical tests. Physical, chemical and biological conditions were monitored in the shipwreck sites. The archaeometric results are consistent with the corrosion tests carried out in modern samples. The corrosion rates are mainly correlated with physical factors, which exert a direct impact on material degradation, and in turn control the hydro chemical and geochemical characteristics, affecting the development of biological communities.
1 INTRODUCTION The large number of discovered shipwreck and another typology of underwater archaeological sites, as well as the high cost of extraction, stabilization and storage, make infeasible the extraction and subsequent conservation process. In addition, past experiences have revealed weakness and difficulties in the stabilization techniques, which might endanger underwater cultural heritage (UCH). These reasons have led to consider the in situ preservation option that has been included among the main principles of UNESCO Convention on the Protection of the Underwater Cultural Heritage 2001 (UNESCO, 2002: 53-66). It is well known that stability, degradation and corrosion rates of different materials depend on environmental marine conditions. Shipwreck site formation and degradation process are influenced by physical processes, chemical conditions and biological factors (Wheeler, 2002). Several experiences of in situ protection proposal, mainly with a reburial process involved, has been accomplished and evaluated in last decades (Gregory et al., 2012). However, the effect in degradation process rates in different materials still today is not yet closing. Monitoring programs and evaluation of in situ protection projects have showed that the protection degree and deterioration rates may vary widely due to changing marine environmental conditions (Brouwers, 2008), especially in coastal areas. Thus, the design of an in situ conservation project to protect materials associated with UCH have to be accompanied with the study of the surrounding environmental conditions. Moreover, with the understanding of the relationship between the degradation processes and the marine environmental factors, including hydrodynamic variables, hydrochemical and geochemical features, sedimentary dynamics and biological communities present in the area. The main aim of this work is to assess the contribution of environmental marine conditions in the degradation process of underwater archaeological metallic materials.
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2 MATERIALS AND METHODS 2.1 Studied sites Located near the Bay of Cadiz, in the southwest coast of the Iberian Peninsula, the two archaeological sites are associated with Fougueux and Bucentaure ships. Both vessels, belonging to the combined Franco-Spanish fleet in the Battle of Trafalgar (1805), were sunken during the violent storm that struck the coast of Cadiz after the battle. The ship S.M.I. Bucentaure, represent a scattered shipwreck where a total of 22 iron guns, remains of an anchor and other metallic artifacts are preserved. The site is located in the outer Bay of Cadiz, on the mixed rocky-sandy bottom at 12 m depth. Meanwhile, in Fougueux site, important portion of the hull structure is preserved, along with 25 cannons and an anchor. Fougueux is seated on a sandy bottom at 7 m depth in front of the Sancti Petri sand spit. 2.2 Marine environmental conditions Hidrodymanics and wave climate characterization was conducted in the studied areas. Local time series of waves and currents at the study sites were acquired using ADCP (AWAC) and electromagnetic current meter (Infinity-EM). Also wave climate analysis in the two study areas was carried out. For this purpose, historical wave hindcasts time series in depth water was propagated using Oluca-sp propagation model (GIOC, 2003). In this way, wave series with 44 year duration was obtained in the study areas and a probabilistic analysis was performed. For sediment characterization granulometric analysis of sediment samples collected in Fougueux and Bucentaure sites was carried out using dry sieving method. The sediment mobility and the geomorphological changes in the shipwrecks sites were evaluated by time lapsed bathymetric surveys and the derived accretion-erosion model. The physical-chemical properties of the surface sediment layers were analyzed in both archaeological sites. Sediment cores 60 cm length and 5.7 cm in diameter were manually extracted with scuba equipment. Afterwards in lab, were measured pH, oxidation reduction potential (ORP), porosity and total organic carbon (TOC) parameters at regular intervals of 3 cm. The physical-chemical properties of the water column in both studies areas were monitored. In situ measurements were collected using a multiparameter probe (Hidronaut-305). Periodically, salinity, temperature, pH, redox potential and dissolved oxygen parameters were measured and recorded. The measurements were performed in the whole water column, which allowed to evaluate parameter changes with depth. In addition data-loggers were used to collect time series of temperature and turbidity at the bottom layer. A characterization of benthic community on rocky seabed was carried out at the archaeological sites. On the other hand, evolution of benthic community on artificial substrates was analyzed. For this purpose, a rack with panels 20x30 cm2 of different materials (copper, brass, iron cast, cast, pine, oak) were placed on sediment seabed, and on rocky seabed in each study site. Studies of the biological community in natural substrate and artificial substrate were conducted using image analysis techniques, and sample collection for identification. Abundance of species was calculated using Fixed Point Quadrat technique (Van Rein et al. 2011). Subsequently, analysis multivariate by permutations of variance (PERMANOVA (Anderson, 2001), has been used to test the differences between the various factors analyzed. Differences between samples were plotted by nMDS analysis (non-metric multidimensional scaling). 2.3 Corrosion determination in modern samples Field exposure tests of modern metallic samples (iron, iron cast, copper and brass) similar to the most common archaeological metallic materials were conducted at the studies sites. The corrosion rates of the 7 cm x 3 cm samples mounted in rack and subject to dissimilar environment (permanent burial (H3), continuously exposed (H1), and alternatively reburial and exposed (H2) were periodically measured after 6, 12 and 18 months exposure times. In order to know the corrosion rates, electrochemical test were conducted. On one hand electrochemical experiments were performed on the samples using a Solartron Potenciostat. Polarization curves were registered in different ranges (from ± 50 mV vs. Ecorr) after 1h open circuit potential, at polarisation rate of 0.1667 mV/s. Corrosion rates at mm/year and another parame-
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ters such as the polaristion resistance, Rp, were obtained in the range between ±20 mV vs. Ecorr. (Mansfeld,1976; ASTM G 59). Also a mass loss test following ASTM G1 procedure was realized in order to evaluate metal and alloys damage after the mentioned exposures time. 2.4 Previous Archaeometric study A previous archaeometric study was carry out in both study sites. In order to evaluate the degree of stability of the archaeological objects (cannons and anchor) located in the study sites. In both archaeological sites some cannons and anchors were selected as targets to establish their current conservation status and assess the prospects for in situ conservation. First, a partial de-concretion task was carried out, which allowed in situ measurements of pH and corrosion potential Ecorr, following the method patented by Bethencourt (2002). The prediction was made by applying the linear relationship between the logarithm of the corrosion rate (Vcorr) and the corrosion potential of iron in seawater (Ecorr) (Macleod, 1995; Gregory, 1999)
log Vcorr = M E corr + C
(1)
Where M and C are parameters of the linear fit. The corrosion rate was estimated as the thickness of the measured graphitic concretion divided by the number of years in immersion of the object. The thickness of layer concretion was measured by gauge, making a hole in the object by using an air drill attached to a compressed air cylinder according to the procedure described in Bethencourt et al., 2002. The corrosion potential measurements were performed using a Data Sheet H1 Bathycorrometer Buckley Ltd., cathode potentiometer which determines the corrosion of the underwater structures. 3 RESULTS AND DISCUSSION 3.1 Environmental marine conditions Hydrodynamic and wave variables were differences between both archeological sites. As current measurements shown, Bucentaure is subject to stronger tidal current, with the main tidal harmonic constituents, lunar semidiurnal tide (M2), reaching up 0.20 m s-1, whereas at Fougueux site is limited to 0.10 m s-1. In addition, wave propagation modeling results show remarkable dissimilarities in the studies areas. The significant wave height (Hs) at Fougueux is higher during 78% time along a year (Fig.1.a). Beyond this difference, in case of Fougueux area, during extreme storms (Hs>3.85 m) wave breaking occur, inducing the suspension and transport of great amount of sediments. Furthermore, the wave orbital velocity near the bottom, is always greater in Fougueux site due to a shallower seabed. Consequently, the shear stress induced by waves is markedly larger at Fougueux site, implying a higher remobilization of sediments. On the other hand granulometric analysis shows differences between Fougueux and Bucentaure sites. In Bucentaure, sediment can be classified as moderately sorted very fine gravelly coarse sand (D50 = 1.095 mm), while in the Fougueux site the sediment can be classified as well sorted fine sand (D50 = 176.8 mm). Coarse grain size in the sediment implies more difficulties for resuspension and transport than smaller grain size. In addition well sorted sediment in Fougueux is correlated with the high energy induced by waves. Accretion-erosion models reveal major changes in Fougueux area unlike unchanged measured in Bucentaure site. The measurement in hydro-chemical variables analyzed show similar values in the study sites due to their proximity and the little difference in depth. Annual temperature variations occur at both studies sites with similar range, from 14 º C reached during March up to 24 ºC measured on September. It should be noted in the deeper part of the profiles, that greater temperatures changes occur at the Fougueux site. The salinity recorded remained around 36 psu, without significant changes in the water column. The density profiles show a well-mixed water column, although with a slight pycnocline associated with daily thermocline.
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Figure 1. (a) Log normal distribution function of significant wave height. (b) nMDS of different communities of sessile organisms that settled in the different experimental panels, in each sampled month and location. F = Fougueux; B = Bucentaure. (stress = 0.13).(c) Graphical Representation by nMDS (stress = 0.01) of the benthic community sampled by video transects during cold season (W) and warm season(S).
Concerning to geo-chemical characterization, as ORP (indicator of oxygen content) show, in Fougueux site, beyond 15-27 cm, sediment has anoxic conditions. Meanwhile in Bucentaure site anoxic zones are not present in the measurements, due the short length reached by cores. In the first 15 cm where the data are comparable, we observe a higher redox potential that would be associated with higher oxygen content at this site. The pH values are similar in two sites, closeness to sweater value (pH=8), and don’t significant variation where found in profiles. Low COT concentration characterizes the studies areas. Lightly higher values were found in Bucentaure site, probably correlated with higher rates of primary production and closeness to the mouth of Guadalete river. Regarding to biological characterization on artificial substrates, panels of copper and brass doesn’t experimented colonization due to the biocidal nature of copper. The degree of colonization increased in the case of cast and iron cast panels. The panels of pine and oak have showed a greater colonization. There are significant differences between the panels placed on sediment seabed, these have not been colonized and remained partially buried, and panel exposed on hard substrate has been colonized and presented greater coverage rates. Figure 1.b show the nMDS of the benthic community developed on artificial substrate in Fougueux and Bucentaure site for every month sampled. The dissimilarities in community evolution can be noted after only after two months of exposure; differences are markedly greater after 15 month of exposure. After two months algae were the largest group to determining the differences between sites. However, after 15 month of exposure, mollusks, bryozoans, annelids and barnacles also contributed to differentiate the community in both sites. Algae, Teredo and Escaroides navalis coccinea were more abundant in Fougueux site, whereas Filograna implexa, Spirobranchis triqueter and Balanus sp. were more profuse in Bucentaure site. The nMDS (Fig 1.c) show significant differences between biological communities developed on natural substrate in the studied zones. It should be note that benthic community in Bucentaure site remains unchanged, unlike seasonal changes observed in Fougueux site. In the latter, the main species that characterized the community are algae. Cystosseira sp, Halopithys incurva, Laurencia obtusa, or Plocamium cartilagineum., In Bucentaure algae were found, although also contributed significantly to the differences species of sponges (Aplysina aerophoba, Dyc-
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tionella sp., Incrustans or Dysidea), squirts (Ecteinascidia turbinata) or polychaetes (Filograna implexa). 3.2 Corrosion determination in modern samples Figure 2 show the corrosion rates as a result of mass loss test accomplished for the different exposure times. In order to perform a comparative analysis between sites mean value in each station was calculated from continuously exposed (H1) and alternatively reburial and exposed (H2) locations. As Figure 2 illustrates the highest rates of corrosion correspond to the Fougueux site. This pattern is common to all materials tested with the exception of brass. Cast and iron cast present the higher corrosion rates with similar values among 0.15-0.30 mm/year. However, the behavior and evolution during exposure time is different, thus meanwhile cast corrosion rate decrease with the growing of layer formed by corrosion product, the corrosion rate in iron cast continue to increase during all test performed. Corrosion rates of brass and copper were markedly lower with values among 0.03-0.09 mm/year. In the case of brass, initially corrosion rates were higher in Bucentaure site, although after 18 month exposure also was slightly greater in Fougueux site.
Figure 2. Mass loss test results. Evolution of corrosion rates of different materials analyzed. (a) Iron cast. (b) Cast. (c) Brass. (d) Copper.
3.3 Archaeometric study result Following methodology outlined in section 2.4 a total of four measurements were performed, distributed over nine months, allowing to obtain the average value of Ecorr. The maximum error don`t exceed the + / - 25 mV, justifying the use of average value. Table 1 show the linear fit parameters calculated according to Equation 1. Result show higher corrosive process in metallic artifact located in Fougueux site after two centuries of exposure. Thus, material loss due to uniform corrosion on cannons located in Fougueux site vary from 0.127 to 0.246 mm/year, whereas corrosion rates measured on cannons located in Bucentaure site was significantly lower with values of 0.073 to 0.118 mm/year. In addition, it should be noted the different thickness founded in biological concretion. While average thickness was only 5mm on cannons located on Fougueux site, in the case of cannons located in Bucentaure site biological concretion reach up to 30 mm thick. Table 1. Linear fit parameters M_________________________________________ and C calculated for each studied site according to Equation 1. Shipwreck site M C ______________________________________ Bucentaure
2.5015
0.3775
Fougueux 2.5810 0.5913 _________________________________________
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4 CONCLUSION The results of monitoring studies carried out on Fougueux and Bucentaure sites, combined with metallic material degradation test and an archaeometric characterization of artillery located in both sites, have allowed asses relationship between environmental marine condition and degradation process of the underwater archaeological metallic material. Physics conditions have a crucial role in metallic material degradation, being the most notable difference founded among Bucentaure and Fougueux site. Thus, higher rates of corrosion on artillery were measured in Fougueux site, which is subjected to higher energetic conditions due to wave action. These results are consistent with corrosion test carry out in modern samples. Physics factor exert control over degradation rates in two primary ways. On one hand, the great rates of sediment remobilization and transport induced by waves in Fougueux site could cause the damage by direct mechanical effect on metallic material as well as removing the product corrosion layer developed on these. On the other hand, abrasive and mechanical effect of sediment on the growth of the calcareous concretion. This effect may result in the decrease of thickness, having a direct negative impact on their conservation status. Physical and hydro-chemical conditions, can contribute to development different types of biologic benthic community: dominated by algae or in turn with a greater presence of sponges, squirts and polychaetes, whose calcareous depositions seem to contribute positively to the UCH conservation. ACKNOWLEDGEMENTS This study has been supported by project ARQUEOMONITOR CTM2010- 16363 (Spanish Ministry of Economy and Competitiveness). We wish to thank the Scientific and Technological Diving Unit of the University of Cadiz who assisted us in sampling expeditions.
5 PREFERENCES ASTM G 59: Practice for conducting potentiodynamic polarization resistance measurements. Bethencourt, M.; Botana F. J., &Marcos, M. 2002. «Sistema combinado para el registro y la conservación arqueológica subacuática in situ». España. Patente de invención n.º 2221525, 2002-05-24. Brouwers, W., Manders, M. 2008. Machu: Managing Cultural Heritage Underwater. Vitruvius, 16-23. GIOC(Grupo de ingeniería de costa) (2003). “OLUCA –S.P 2.0. Universidad de Cantabria. Ministerio del Medio ambiente. Dirección General de Costas. p. 170. Gregory, D., Jensen, P. & Strã¦Tkvern, K. 2012. Conservation And In Situ Preservation Of Wooden Shipwrecks From Marine Environments. Journal of Cultural Heritage, 13, S139-S148. Mansfeld, F. 1976. The polarization resistance technique for measuring corrosion currents, in: M.G. Fontana, R.W. Staehle (Eds.), Advances Corrosion Science Technology, vol. VI, Plenum Press, New York, 1976, pp. 163–261. Van Rein H, Schoeman DS, Brown CJ, et al. 2011. Development of benthic monitoring methods using photoquadrats and scuba on heterogeneous hard-substrata: a boulder-slope community case study. Aquat Conserv Mar Freshw Ecosyst 21:676–689. Wheeler, A. J. 2002. Environmental Controls on Shipwreck Preservation: The Irish Context. Journal of Archaeological Science, 29, 1149-1159. UNESCO-UCH (2002): «Convención sobre la Protección del Patrimonio Cultural Subacuático». Resolución aprobada, previo informe de la Comisión IV, en la 20ª sesión plenaria, el 2 de noviembre de 2001. Actas de la Conferencia General, 31ª reunión (París, 15 de octubre - 3 de noviembre de 2001). París: Organización de las Naciones Unidas para la Educación, la Ciencia y la Cultura, pp. 53-66.
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