In situ protection and conservation of the Zakynthos wreck
In situ protection and conservation of the Zakynthos wreck
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ABSTRACT
Over the last 40 years a large number of shipwrecks have been recorded around the world. Recently, the preservation of several historic wooden ships, has highlighted the work of maritime archaeology and provided public access to important finds of cultural heritage.
The aim of this study was to investigate the preservation of the Zakynthos wreck (Greece).
The first part of the work investigated the protection of the wreck timbers during and after excavation and the second part the most appropriate method for their conservation.
In order to understand the processes that contribute to the preservation and degradation of the Zakynthos wreck material, the ecology and nature of the pelagic and benthic environments of the Zakynthos site were investigated. Data obtained from 12 months monitoring of the site showed a normal marine open-circulation environment with a high biodeterioration risk. Major deteriogens were molluscs, and to a lesser extent crustacean borers and lignicolous fungi. Pine, beech and oak samples exposed for 24 months at the site showed high deterioration rates. Physico-chemical and microbiological analyses of the benthic environment showed it to be a sandy, low energy anaerobic sediment. Based on this information, an in situ protection method for the timbers exposed during and after excavations was developed.
The geotextile “Terram”, a synthetic product made of polyethylene and polypropylene, was tested in vivo at Zakynthos and Langstone Harbour (UK) and in vitro for its suitability as a physical barrier system against marine boring organisms. Four different grades of Terram were used : 500, 1000, 2000 and 4000, and controls. Terram grades 2000 and 4000 provided effective protection against marine borer infestation in both laboratory and field studies. In situ application of Terram 4000 at the Zakynthos site demonstrated the mechanical resistance of the fabric and its stability in the marine environment. After one year the geotextile was covered by sand and colonised by marine fauna and flora. It returned the excavated site to a stable anaerobic environment and ensured the protection of shipwreck timbers buried within it. Terram 4000 is recommended for the in situ protection of wreck timbers in marine archaeological sites.
The majority of the archaeological material found at Zakynthos site was waterlogged wood and the extent of its degradation affects significantly its conservation. Characterisation of the degree of deterioration of the oak timbers encountered at the Zakynthos shipwreck was determined by examination of their micro-morphological and physico-chemical properties. The preservation condition of oak, pine and birch samples from the Mary Rose wreck was also determined in order to obtain a wider range of wood species and conditions.
A comparative study of conservation treatments involved three low (PEG 200, BREOX 50A20, BREOX 50W200) and two high (PEG 4000, BREOX 50W4000) molecular weight water-borne polymers. These were tested in a one- and two-stage impregnation systems, followed either by air or freeze drying. In the one-stage impregnation system followed by air drying BREOX 50A20 and BREOX 50W 4000 were found to be unsuitable. PEG 200 provided consolidation to the lightly degraded samples and PEG 4000 to the heavily degraded ones. Polymer content estimated for the low molecular weight chemicals showed that PEG 200 was retained to a greater extent than either BREOX 50A20 and BREOX 50W200. When BREOX 50A20 was used as a pre-treatment to freeze drying in a one-stage impregnation system it provided effective consolidation for waterlogged wood and gave better aesthetic results than either PEG 200 or BREOX 50W200. Samples treated with this polymer also displayed very low values of moisture content at the equilibrium state.
In a two-stage treatment system followed by air drying, BREOX 50A20 showed compatibility with PEG 4000 and displayed the best ASE for oak and pine samples. Similar ASE values were exhibited by PEG, BREOX 50A20 and BREOX 50W200 in a two-stage system followed by vacuum freeze drying. Finally, all hardwoods examined displayed better ASE values in all impregnation systems when followed by vacuum freeze drying rather than air drying.
In conclusion, the results of this study indicated that Terram 4000 is an effective physical barrier system for the in situ protection of excavated wreck timbers. Furthermore, they indicate that if the Zakynthos wreck is to be conserved as a complete structure, a two-stage impregnation system followed by air drying using, BREOX 50A20 and PEG 4000 is the preferred treatment. Conversely, if the wreck is be conserved as separate timbers and then reassembled, PEG 200 or BREOX 50A20 used in a one-stage impregnation system followed by freeze drying is the most appropriate.
Over the last 40 years a large number of shipwrecks have been recorded around the world. Recently, the preservation of several historic wooden ships, has highlighted the work of maritime archaeology and provided public access to important finds of cultural heritage.
The aim of this study was to investigate the preservation of the Zakynthos wreck (Greece).
The first part of the work investigated the protection of the wreck timbers during and after excavation and the second part the most appropriate method for their conservation.
In order to understand the processes that contribute to the preservation and degradation of the Zakynthos wreck material, the ecology and nature of the pelagic and benthic environments of the Zakynthos site were investigated. Data obtained from 12 months monitoring of the site showed a normal marine open-circulation environment with a high biodeterioration risk. Major deteriogens were molluscs, and to a lesser extent crustacean borers and lignicolous fungi. Pine, beech and oak samples exposed for 24 months at the site showed high deterioration rates. Physico-chemical and microbiological analyses of the benthic environment showed it to be a sandy, low energy anaerobic sediment. Based on this information, an in situ protection method for the timbers exposed during and after excavations was developed.
The geotextile “Terram”, a synthetic product made of polyethylene and polypropylene, was tested in vivo at Zakynthos and Langstone Harbour (UK) and in vitro for its suitability as a physical barrier system against marine boring organisms. Four different grades of Terram were used : 500, 1000, 2000 and 4000, and controls. Terram grades 2000 and 4000 provided effective protection against marine borer infestation in both laboratory and field studies. In situ application of Terram 4000 at the Zakynthos site demonstrated the mechanical resistance of the fabric and its stability in the marine environment. After one year the geotextile was covered by sand and colonised by marine fauna and flora. It returned the excavated site to a stable anaerobic environment and ensured the protection of shipwreck timbers buried within it. Terram 4000 is recommended for the in situ protection of wreck timbers in marine archaeological sites.
The majority of the archaeological material found at Zakynthos site was waterlogged wood and the extent of its degradation affects significantly its conservation. Characterisation of the degree of deterioration of the oak timbers encountered at the Zakynthos shipwreck was determined by examination of their micro-morphological and physico-chemical properties. The preservation condition of oak, pine and birch samples from the Mary Rose wreck was also determined in order to obtain a wider range of wood species and conditions.
A comparative study of conservation treatments involved three low (PEG 200, BREOX 50A20, BREOX 50W200) and two high (PEG 4000, BREOX 50W4000) molecular weight water-borne polymers. These were tested in a one- and two-stage impregnation systems, followed either by air or freeze drying. In the one-stage impregnation system followed by air drying BREOX 50A20 and BREOX 50W 4000 were found to be unsuitable. PEG 200 provided consolidation to the lightly degraded samples and PEG 4000 to the heavily degraded ones. Polymer content estimated for the low molecular weight chemicals showed that PEG 200 was retained to a greater extent than either BREOX 50A20 and BREOX 50W200. When BREOX 50A20 was used as a pre-treatment to freeze drying in a one-stage impregnation system it provided effective consolidation for waterlogged wood and gave better aesthetic results than either PEG 200 or BREOX 50W200. Samples treated with this polymer also displayed very low values of moisture content at the equilibrium state.
In a two-stage treatment system followed by air drying, BREOX 50A20 showed compatibility with PEG 4000 and displayed the best ASE for oak and pine samples. Similar ASE values were exhibited by PEG, BREOX 50A20 and BREOX 50W200 in a two-stage system followed by vacuum freeze drying. Finally, all hardwoods examined displayed better ASE values in all impregnation systems when followed by vacuum freeze drying rather than air drying.
In conclusion, the results of this study indicated that Terram 4000 is an effective physical barrier system for the in situ protection of excavated wreck timbers. Furthermore, they indicate that if the Zakynthos wreck is to be conserved as a complete structure, a two-stage impregnation system followed by air drying using, BREOX 50A20 and PEG 4000 is the preferred treatment. Conversely, if the wreck is be conserved as separate timbers and then reassembled, PEG 200 or BREOX 50A20 used in a one-stage impregnation system followed by freeze drying is the most appropriate.
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