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The conservation of a 2nd-century AD shipwreck represents a challenge in many ways: the amount of material, different ones such as waterlogged wood, iron, lead, textiles, pitch, among others. A global project has to be planned, meaning that scale adaptations had to be thought of taking into account the exceptional size and diversity matters. On top of it, a common thread with pyrite has to be taken into account to avoid acidification by little footsteps at each conservation care stage. To do this, a complete dismantling has occurred, allowing the removal of 26 meters of waterproofing material which happened to be pitched textiles. To explore the data embedded inside, a new unfolding protocol had to be elaborated; that respected their fragility. New issues arose from this work, allowing to link the textiles to the barge, and also opened new exploration fields of an exceptional set of roman textiles.
The Lyon Saint-Georges barge from the 2nd century AD has now been treated with PEG 2000 for 4 years. A high concentration rate of pyrite, up to more than 40 wt % in certain areas, was detected when she it arrived in ARC-Nucléart, and special care was needed to face this problem. What feedback do we have on the various tasks made to prevent the wreck from acidification and what are the current conservation conditions of the barge? Several tasks were carried out to prevent from acidification while the wreck was still waterlogged. First, the complete dismantling, allowing the removal of 2100 nails and corrosion products before treatment in PEG 2000 solution. Then the constant monitoring of the solutions, with a dynamic system of cleaning, oxygenation and ion-catching resins to remove the solubilized salt, helped by maintaining the pH in the region of 5-5.5. After freeze-drying, complementary coring was done, mainly in the nails’ holes, and a basic-buffer coating with Disodium Sebaçate was then applied. Now the wreck is stored in Grenoble, under air-conditioned monitoring that keeps a low-rate of relative humidity (under 50%). We observed several initiations of acidification, with areas becoming light grey and demonstrating a peeling skin aspect, but these areas never became wet yet, as already usually observed on acidic wood treated with PEG. After checking the pH in these areas, it was measured a minimum of 3. This acidification resulted in a very superficial dry layer, easy to remove in one or at the most several interventions. Thus, the stabilization of the wood in these conditions seems effective. Now work has started with curators to prepare the museum area for the arrival and installation of the wreck for 2022 and to establish a long term conservation plan, providing on-going detailed observations and ensuring optimal environmental conditions during the public display of the barge.
A pre-restoration diagnosis revealed a high amount of pyrite in the wood of the Lyon Saint-Georges 4 shipwreck (end of the second century). The occurrence of this phase is supposed to result from the microbiologically influenced corrosion of the iron fasteners. So, all the nails and metallic elements were removed from the remains before treatment and the wreck was consolidated by polyethylene glycol impregnation coupled to a specific desalination process. Treated and non-treated samples extracted from the wreck were studied in order to identify the iron/sulfur-containing compounds present in the wood before and after treatment and figure out its effect. Sample analyses relied on an original approach combining magnetic characterization methods and more common elemental and structural analysis methods. The results showed that the treatment was effective in removing soluble salts. However, a large amount of unstable iron sulfides remained inside the wood. © 2019, © The International Institute for Conservation of Historic and Artistic Works 2019.
Pyrite and greigite were identified in the wood of two ancient shipwrecks using an original multi-technique analytical approach. Structural characterization methods such as environmental scanning electron microscopy, micro-Raman spectroscopy and X-ray diffraction were combined with magnetic measurement methods, such as magnetic susceptibility measurements and isothermal remanent magnetization acquisition curves. This is the first time that magnetic measurement methods are used in the field of cultural heritage to study wet organic archaeological materials. They proved to be particularly suitable to detect with a very high sensitivity ferromagnetic s.l. mineral phases inside waterlogged wooden samples, i.e. in the bulk. The occurrence of iron sulfides in archaeological shipwrecks extracted from waterlogged environments is usually attributed to microbiologically influenced corrosion of iron fasteners. This study demonstrates that the nature of the identified iron sulfides is consistent with a step-by-step in situ anoxic oxidation process of mackinawite.
LSG4 (Lyon Saint-Georges n°4) is a gallo-roman shipwreck discovered in 2004 in Lyon, France, during a rescue excavation, and then stored in a lake for ten years with two others wrecks from the same period. Over the past two years, conservators have been working tight with the archaeologist in charge of the LSG4 shipwreck and now we present how we built our fruitful collaboration. We managed to raise the six parts from the lake and transport them to Arc Nucléart in January 2014. We were considering further dismantling, for handling issues, but we had to review all plans because of the presence of iron and sulfur compounds. Decision was taken to completely remove nails and, hence, to lay down every piece of wood. It was a unique opportunity to work together. The archaeologist took data about construction and upkeep after dismantling and before PEG treatment. As conservators cleaned every inch of the wood, they saw noticeable details they showed to the archaeologist. We also chose to separate the differents materials in order to ease their conservation, adapted for each material, and archaeological analysis, based on our common experience. After freeze-drying, new observations can be conducted, because of the slight wood shrinkage during this operation, that enlighten treenails for example. Conservators help the archaeologist to do his task by preparing planks, then they use his plans for their own recording with the on-going operation of complementary coring. In 2016, we worked on the support together to find the right position for elements. At each step of the conservation process, working together increases significantly knowledge, to still take better care of the remains. We’re mainly working on avoiding acidification for this wreck; news are good for now, and we hope it will go on! After more than a year of collaboration, the archaeological part and the conservation part are equal and raise various questioning. After years of specialization in each discipline, it is now time to converge and see what we can do together. Archaeologist can make observations after conservator’s intervention, and conservator can understand needs of archaeologist and integrate them in the conservation process.
The biologist of ARC Nucleart took ten years to elaborate regeneration systems and protocols for PEG solutions treatment used for the preservation of waterlogged wood. By experience, contamination comes in the treatment solution from the wood itself, but also sometimes from the various biocides used in the past. Gradually, the solution become insane to be longer used and is thrown in great quantity. Our approach is original; instead of adding exogenous substances to control contamination (biocides), we explored the path to remove all the contaminating agents. For biological agents (bacteria, yeast …) ultra violet lamps are used to disinfect the aqueous solution permanently. In spite this treatment, there is still biofouling staying in the solution. Consequently special filters were found in order to remove all that matters in suspension (weaved filter, active coal, ionic exchange resins), but also contribute to indirect disinfection. From the agro-food industry, micro-filtration was chosen. A fruitful collaboration was established with the filters’ fabricant to elaborate a complete filtration’s solution: loop circuit, with pump and flexible miscellaneous filtration elements. Finally, the process is complete and allow to destroy all the bacteria and micro-organisms coming from the waterlogged wood and developed in anaerobic environment, by oxygenating solutions with skimmers coming from the swimming-pool industry. With the combination of all these techniques, it is possible to regenerate efficiently PEG solutions 24h/24h. The efficiency of this process, was controlled by analysis of PEG’s degradation, using FTIR monthly, and HPLC every six months. No changes has been shown over this past ten years. With this experimentation, we improved the PEG treatment process in terms of efficiency, but also in terms of environmental and economic considerations. It works well because ARC-Nucléart didn’t bought PEG over the past five years (in spite of successive big treatments for the Arles Rhône 3, Antibes, and Lyon Saint-Georges 4 shipwrecks), neither PEG have been thrown.
ARC-Nucléart has developed a system for regenerating PEG (polyethylene glycol) baths, used in the treatment for consolidating waterlogged archaeological wood progressively degraded by bacteria, by substances that have dissolved in the water and by particles added by the wood itself. The novelty of this approach lies in its method of replacing the use of biocides with a fourfold method of extraction and neutralizing contaminants: removal of particules and yeasts by micro-filtration; removal of ions by fluidized beds of resin/activated charcoal; disinfection of the PEG solution by running it past an UVC lamp and by air bullage (oxygenation) of baths. Using these measures to regenerate the baths markedly reduces the economic and environmental impact of the treatments at the same time as improving their quality. Keywords. Archaeological wood, recycling PEG treatment baths, filtration, UVC.