Aurélie Verney-Carron

Des blocs de verre archéologique provenant d’une épave découverte près de l’île des Embiez (Var) en mer Méditerranée ont été étudiés en raison de leur analogie morphologique avec les verres nucléaires et de leur environnement connu et stable. Fracturés à l’issue de leur élaboration (comme les verres nucléaires), ces verres se sont altérés près de 1800 ans en eau de mer. Ce travail a abouti au développement et à la validation d’un modèle géochimique capable de simuler l’altération d’un bloc de verre archéologique fracturé au bout de 1800 ans. Les expériences ont permis de déterminer les constantes cinétiques des mécanismes en jeu (interdiffusion et dissolution du réseau vitreux) et les paramètres thermodynamiques (affinité, phases secondaires) de ce modèle. Celui-ci, implémenté dans HYTEC a permis de simuler l’altération de fissures sur 1800 ans. La cohérence des épaisseurs d’altération simulées et des valeurs mesurées sur les blocs valide la capacité prédictive du modèle. Ce modèle permet alors d’expliquer les résultats issus de la caractérisation du réseau de fissures et de son état d’altération. Les fissures de la zone externe du bloc sont les plus altérées du fait du renouvellement rapide de la solution, alors que les fissures internes ont des épaisseurs très fines à cause du couplage entre l’altération du verre et le transport des éléments en solution (effet de l’ouverture initiale et du colmatage). Les résultats expliquent non seulement les épaisseurs les plus fines, mais aussi leur variabilité. Le comportement analogue des verres archéologiques et nucléaires permet d’envisager une transposition de ce modèle aux verres nucléaires en condition de stockage géologique

Built cultural heritages are exposed to environmental factors such as atmospheric pollution, especially in urban areas. Reaction between sulphur dioxide SO2 and calcite CaCO3 from calcareous stone forms a gypsum crust CaSO4.2H2O, commonly called “black crust”. This crust acts as a proxy of ancient atmospheric pollution due to the deposition of particles such as soot, organic compounds, heavy metals, etc. However, to prevent stone degradation, restore the initial aesthetic and the clarity of the architectural lines, black crust are usually removed by cleaning during a restoration project. Traditional techniques like mechanical cleaning are used in most cases. Yet, the inhalation of black crust particles may result in severe health issues. Lead, emitted from coal combustion and leaded gasoline during 20th century and deposited in black crusts, may cause damage to the cardiovascular, nervous, renal and reproductive systems. According to previous studies, its bulk concentration ranges from a few dozen to thousands ppm depending on the city, the sampling location on the buildings and other factors. In France, prior to any black crust cleaning, the acid-soluble lead concentration must be measured by wipes rubbed on façade and must not exceed 1000 µg.m-2. Otherwise, several measures must take place to ensure the safety of operators. However, these wipe tests were originally standardized for flat, horizontal and smooth surfaces. Moreover, wipes can only dissolve the top layer of a black crust, even though the distribution and behaviour of lead within black crust is not well-known in literature.To address these questions, black crust samples collected in France were analysed using electron microprobe to determine the location and quantify lead particles. The morphology of these particles was further characterized using SEM-EDS. In addition, bulk analyses were also performed by ICP-MS to quantify the total lead concentrations. Results indicate that lead concentrations are high and that lead is mainly located in small particles and correlated with combustion metals such as iron. The results are key to optimize risk assessment and in situ measurements.

This paper reviews results published by the International Co-operative Programme on Effects on Materials including Historic and Cultural Monuments (ICP Materials) with emphasis on those obtained after the turn of the century. Data from ICP Materials come from two main sources. The first is through exposures of materials and collection of environmental data in a network of atmospheric exposure test sites mainly distributed across Europe. Corrosion of carbon steel has continued to decrease during the period 2000–2020 but corrosion of zinc only up until 2014, and the trend in zinc corrosion is only visible when examining four-year data. Surface recession of limestone as well as soiling of modern glass show no decreasing trend during 2000–2020. The second is through case studies performed at heritage sites across Europe. Risk analysis of corrosion and soiling for twenty-six sites indicate that currently soiling is a more significant maintenance trigger than corrosion. Costs for maintaining heritage sites are substantial and costs attributable to air pollution is estimated from 40% to as much as 80% of the total cost. Future directions of the program are work on effects of particulate matter, improving the scientific basis for the work, and making the monitoring data publicly available.

Stained glass windows are a precious heritage to pass on to future generations. However, medieval stained glass windows are particularly altered due to their chemical composition and the effects of climatic (mainly water and temperature), environmental (pollution) and biological factors. In this review, we present the alteration patterns observed on ancient Si-K-Ca stained glass windows. To better understand their formation mechanisms and determine the alteration rates, different exposure campaigns to the current atmosphere in a position sheltered from rain or not and laboratory experiments in aqueous medium or in gaseous phase have been conducted. Either model glass or ancient stained glass windows were studied. Isotopic tracers (D,¹⁸O,²⁹Si) have been used as they constitute a powerful tool to elucidate the involved processes and to measure their kinetics. Thanks to all of these data, an alteration scenario of medieval stained glass alteration is proposed. Besides, the extrapolation of kinetic data based on several hypotheses over seven centuries gives very consistent results compared to the ancient stained glass samples.

Since the Industrial revolution and due to increasing anthropogenic emissions, the composition of the atmosphere has been modified, leading to climate change and pollution. The impacts of pollution were depicted through paintings and writing from the beginning of the 19th century, but pollution measurements are relatively recent. In order to obtain ancient air pollution data, proxies in urban area need to be found.Black crusts formed on limestone and marble monuments in urban area seem to be a good candidate as local proxy. Mainly composed of gypsum (CaSO4.2H2O), they are a chemical alteration pattern resulting from the reaction of the dissolution of the calcite (CaCO3) of the stone and of sulfation by sulphur dioxide (SO2) from the atmosphere. Particulate matter accumulates in the newly formed gypsum layer in sheltered area from the rain, thus giving the black crust a passive sampler potential.To use black crusts as past air pollution archives, samples were collected at Père Lachaise cemetery (Paris) on ancient, dated (1820-1887) and unrestored limestone or marble tombs. Different types of analyses were performed to study sample morphology (by Optical Microscope), particulate matter (by Scanning Electron Microscopy) and chemical composition (especially major elements and trace metals by ICP-AES, LA-ICP-MS). Results underline two important features to use black crusts as past air pollution archives. First, the low variability of chemical composition of black crusts from Père Lachaise cemetery highlights that the black crusts are representative of the site and register the background pollution. Then, the morphology (laminar vs. dendritic) of black crusts is a key parameter to sample black crusts as the stratigraphy is much better preserved in laminar black crusts.

Limestone buildings in urban areas are weathered due to climatic factors, to pollution but also to biological activity. Many studies have focused on microbially-mediated precipitation of calcite but few on their influence on limestone dissolution rates. In this study, a cultivable approach for studying bacterial dissolution of limestone is proposed. The results show, for the first time, that limestone has selected a specific structure in the bacterial communities and that each bacterial class has its own metabolism inducing a different efficiency on the alteration of limestone grains. Cultivable bacterial and fungal strains in our study permit to considerably increase (by 100 to 1,000,000 times) the chemical weathering rates compared to laboratory or field experiments. Individually, the results bring information on the ability to alter limestone by dissolution. Moreover, taken together, a functional ecological adaptation of bacterial and fungal classes to the alteration of the limestone monument has been highlighted. In order to release calcium into solution, these strains slightly acidify the medium and produce low molecular mass organic acids during experiments, especially lactic and oxalic acids.

A growing portion of scientists realises the need to not only alert about climate change, but also change their professional practices. A range of tools have emerged to promote more sustainable activities, yet many scientists struggle to go beyond simple awareness-raising to create concrete transition actions. Here we propose a game-based transition support systemMaTerre180’, which has been designed to build scenarios of greenhouse gas (GHG) emission reductions in the academic community. After providing a common scientific background about the context (global warming issue, its causes and consequences) and setting up a challenge (50% reduction of carbon budget by 2030), the participants belonging to the academic community and its governance bodies immerse themselves into fictional characters, to simulate the behaviour of real research groups. The game has been deployed during the year 2021, with six hundred participants from nine countries and 50 cities. Results explore clear pathways for GHG reductions between 25 and 60%, and a median reduction of 46%. The alternatives allowing the greatest reduction are video communication tools (36%), followed by mutualization of professional activities and voluntary cancellation or reduction, that represent 22 and 14% of reduction, respectively. The remaining 28% of reduction consists of transport alternative, relocation of professional activities, extended duration of some travels, etc. In addition, the analyses pointed out the importance of the guided negotiation phase to bring out some alternatives such as relocation, local partners and computing optimization. An added value of this transition support system is that the information it collects (anonymously) will be used to answer pressing research questions in climate change science and environmental psychology regarding the use of serious games for promoting changes in attitudes and behaviours towards sustainability, and including broader questions on how network structures influence “climate behaviour”, knowledge and the governance of the commons.Modestly,MaTerre180’offers an innovative game-based transition support system to build scenarios of greenhouse gas (GHG) emission reductions in the academic community. It is not simply a question of moving tokens on a virtual gameboard and a playful adjustment of practices, but rather a question of brainstorming about possible and desirable ways of remodelling research and teaching communities and embracing a new paradigm. After tens of workshops, our results show clear pathways for reaching up to 50% GHG reductions and stress the importance of guided negotiations to bring out alternatives to carbonized activities. This first attempt reinforces our belief that scientific engagement is at the heart of the international development agenda and a key approach to tear down the institutional barriers that inhibit the transformation needed to achieve a more sustainable society.

Most stained-glass windows installed during the Middle Ages have deteriorated over time due to climate and pollution. To reconstruct their alteration history over the centuries, evaluate the current environmental risk, and predict their alteration in the future, two modelling methodologies have been used. First, based on the short-term exposure of medieval-type glass in different sites, dose–response functions (DRFs) were established. These DRFs correlate relevant environmental factors (temperature, rain quantity, rain pH, relative humidity, and SO₂ concentration) with the response of the material in terms of alteration layer thickness. The second methodology consists of laboratory experiments that aim at parametrising kinetic laws as a function of specific parameters (temperature, rain pH, and relative humidity). These kinetic laws can be extrapolated over long periods, contrary to DRFs. In this study, we compared both methodologies to simulate the alteration of a model stained glass at different European sites or over different time periods. The results highlighted that the kinetic laws were able to closely represent the data, except for the polluted sites where the alteration was underestimated. This indicated that the dependence of the alteration rate on the pollutant concentrations should be included to improve the model.

A large number of stained glass windows were installed from the 13th century. During the Middle-Ages, most of glass pieces have a Si-K-Ca composition with a relatively low SiO2 content, but high content of K2O and CaO.  This chemical composition means that medieval stained glass deteriorates during environmental exposure, from climate and environmental pollution. These alterations are manifested in the form of an alteration layer and secondary phases (mainly gypsum or syngenite). The alteration layer is generally depleted in K and Ca, but rich in Si, Al and Fe. Its thickness varies up to 300 µm after 6 or 7 centuries of alteration. In order to reconstruct the alteration history and predict the deterioration of stained glass windows in the future, it is necessary to determine alteration rates as a function of the climate and environmental parameters. Several methodologies can be used to achieve this. First, short-term exposures or laboratory experiments can assess the first stages of the alteration and short-term kinetics. From these results, dose-response functions (DRF) were established for sheltered and unsheltered rain conditions. They correlate relevant environmental factors (temperature, rain quantity, rain pH, relative humidity, SO2 concentration) with the response of the materials in terms of alteration layer thickness. The second methodology consists in laboratory experiments that aim at parametrizing kinetic laws as a function of specific parameters (temperature, pH of rain, and relative humidity). These kinetic parameters do not directly consider pollution, but they can be extrapolated over long periods and can be inputs to geochemical models. In this study, we have compared both methodologies to simulate the alteration of a model stained glass at different European sites (using data from the ICP-Materials program). Both models give good results, but the geochemical model tends to underestimate the alteration at polluted sites. This indicates that the pollution via the concentration in SO2 for example should be included to improve the model.