Philippe Malaurent

Contribution of numerical modelling of environmental parameters to the conservation of prehistoric cave paintings: the example of Lascaux Cave

Abstract This study of Lascaux Cave consisted of simulating the evolution of changes in the levels of temperature and humidity both in the air and in the rock. By choosing different models (one-dimensional, three-dimensional, etc.), it was possible to calculate the required variables (temperature, moisture levels, speeds, etc.) at all points inside the cave, to locate zones of high water vapour concentration and to understand the nature of the airflow. The simulations described here provide the first general data on the airflow within the cave and its hygrothermic behaviour. The temperature fields result from natural convection phenomena, which are influenced by the climate outside the cave. From the point of view of air dynamics, we can observe the presence of an overall airflow that starts in the Machine Room (containing the air conditioning system installed in 1958), runs along the ground to the end of each of the branches of the cave, and returns along the cave vault to its starting point. This slow-moving phenomenon suggests the possibility of passive control of the ambient air from the Machine Room. There are localized risk areas where condensation of water vapour can occur, resulting in rapid deterioration of the limestone. Several of these areas are therefore monitored using condensation indicators placed on the cave walls or by visual observation of painted areas. The higher air speeds detected in some areas of the cave result in decay of the prehistoric paintings. The numerical modelling results, confirmed by observations and measurements in situ, should be taken into consideration when managing the conditions within the cave.

Re-establishing an underground climate appropriate for the conservation of the prehistoric paintings and engravings at Lascaux

Abstract The prehistoric paintings and engravings of the Lascaux cave almost disappeared in the 1960s, victims of their own fame. The facilities installed to allow public access to the cave disturbed and destabilized the equilibrium which had been responsible for conserving the caves art. The complexity of the parameters at play raised the question: had the age-old equilibrium, which had kept the rock art in such excellent condition, been irretrievably destroyed? Thirty years of measurements and research have made it possible to examine, in both the short term and the long term, the validity of the decisions that were taken. It was found that the climatic equilibrium of this natural cave, essential to the appropriate control of the underground environment, could be restored. Since 1996, automated data-collection tools, which remain reliable even in harsh environmental conditions, have replaced manual data-collection methods. The continuous monitoring made possible by automatic data-collection heralds a new era in the scientific management of this type of cultural heritage.

Apport de l’analyse colorimétrique à propos de la caractérisation in situ des peintures préhistoriques dans une démarche conservatoire : cas de la grotte Chauvet (Ardèche, France)

Abstract In situ colorimetric determination is a useful quantitative and non-destructive contribution for the characterisation of organic and mineral pigments. It is in accordance with regard to the administrative instructions, which privilege the maximal conservation to secure the integrity of art discovered recently in this extraordinary prehistorical sanctuary. This determination connected with technical statements of archaeologists, help us to understand that many red hand paintings drawn with the palm of the right hand of a man and of a woman or adolescent, were made from one unique paint pot and the mode of retouch of black charcoal drawings.

Hydrochemical and Hydrodynamic Behavior of the Epikarst at the Lascaux Cave (Montignac, France)

This study focuses on determining the hydrodynamic and hydrogeochemical behavior of the vadose zone of Lascaux karst (Dordogne, France). This work is of particular interest for the conservation of the famous prehistoric paintings of the Lascaux Cave. Indeed, unsustainable infiltration into the cave influences the microclimate parameters (temperature, humidity) and may play a role in aerologic phenomena (condensation, drying) that can affect the decorated walls. A continuous monitoring device for physical and chemical parameters (conductivity, pH, temperature, dissolved O2) and fluorescence of organic matter are installed in the epikarstic spring located inside the cavity. In addition, weekly samples are performed at the epikarstic and Haute Fageotte springs. Weekly rainfall (major ions, water isotopes) and soil water (major ions, organic carbon) samples are performed to determine the input chemical signal in the karst system. The results show that water with shorter or longer residence time can be identified during the floods, considering electrical conductivity and the dissolved organic carbon as natural tracers. Moreover, when the system is highly water saturated, water with long residence time is solicited highlighting an increase of the area participating to the flow at the epikarstic emergence. The study of the calco-carbonic equilibrium of the epikarstic spring also confirms these observations. The calco-carbonic equilibrium shows interannual and seasonal variations related to climatic conditions, carbon dioxide concentration in soils and epikarst, and the flow conditions in the vadose zone. The relations between SIc and PCO2eq allow us to recognize the climate influence on the recharge geochemical signal of the Lascaux karst. It would be useful to estimate the global warming impact on the geochemistry of karst water.

Random temperature and humidity models in Atlantic environment

ABSTRACT Moisture and temperature variations have a high influence on building materials behavior, like creep and durability in timber or activity of corrosion in reinforced concrete. Improving the prediction of these behaviors requires a better modeling of these variations. Variations of temperature and humidity recorded during several years at an hourly time step have been analyzed so as to make the part between a deterministic signal (explained by astronomical reasons) and a stochastic part. The variographical analysis for temperature has revealed a correlation structure of about seven days. The humidity is considered as a random variable whose variations are constrained by temperature values and physical laws (air saturation). The combined simulation enables to build synthetic climates, which present the same patterns, in terms of statistical distribution and time dynamics than real data records. These synthetic signals will be used for studying the building materials response under long-term environmental loading. An application to timber durability will be presented in a companion paper.

Decomposition of CO2 Signal in Lascaux Cave

Air CO2 partial pressure (Pco2) in one of the monitored parts in Lascaux cave (Hall of the Bulls, near the entrance) is variable. For the year 2009, three major components of Pco2 were identified: a seasonal component, a low-frequency component and a high-frequency component. As a first step to understand the presence of Pco2 in caves, this study aims to separate these components and quantify their contributions to the Pco2 signal. Seasonal component is calculated with a sinusoid curve fitted to the measured Pco2. This component is subtracted from the measured Pco2. Then, from the remaining value of Pco2, low- and high-frequency components were separated using Fourier transform, threshold filtering of the frequency and Inverse Fourier transform. Seasonal component is the main contributor (82 % on the average); high-frequency component participates 12 % on the average. Low-frequency component is not present all the year; the average participation is 6 %. Finally, to link these three components with other measured parameters such as temperature, water flow and atmospheric pressure, hypotheses were proposed.

Microclimate analysis of deteriorated wall paintings: With restitution of original decoration through imaging

Abstract The restoration of deteriorated wall paintings in an underground environment requires at the outset a complex analytical approach designed to clarify the deterioration processes. These can be identified and prioritized using continuous microclimatic monitoring with multichannel analytical loggers, providing abundant data on climatology, airflow and hydrogeology in real or semireal time. The investigator can therefore have an almost instantaneous idea of the evolving microclimatic conditions of the monument, identifying among other variables the condensation or evaporation phases of the walls and the rising or sinking of the underground water table when the monument ‘has its feet in the water’, as in the case described here of St Emilion (France). In addition, electronic image capture in situ can be used to decode and restitute very damaged paintings that have become difficult to read, with a view to their being eventually presented to the public.