It is a real scientific investigation that researchers from the Jean Lamour Institute in Nancy are currently participating with the “Pierre” group of CNRS. Their mission: Discover the recipe for mortars used in the cathedral by medieval builders.
The case is exciting. It takes us to the Middle Ages with ultra-modern tools, at the forefront of technology. Here in Nancy, samples of material arrived from Notre-Dame de Paris, about twenty stones.From the collapsed arch of the nave and choir“.
Two years ago, on April 15, 2019, a terrible fire broke out. Everyone remembers these pictures of the collapsed arrow. The blocks that make up the arch of the cathedral nave were found scattered on the ground after the fire. A huge archaeological puzzle for scientists. To assist the principal architects, the CNRS Launch large-scale scientific research by inviting laboratories across the region to study building materials: wood, glass, metal and stone.
A unique opportunity to uncover, for example, the recipe for medieval mortars used in Notre Dame. Cedric Mullis, Research Engineer at HisCAnt-MA (History and Cultures of Antiquity and the Middle Ages – Lorraine University) And Jean-Michel Micheling, research professor atJean Lamour Institute (CNRS / Université de Lorraine), he went there at the beginning of March and came back with precious specimens.
Maximum information with few samples.
“We’ll have to try to get as much information as possible with the few samples we have“Jean-Michel Mecheling is totally intrigued and there is a lot of him with the stones in his hands. He gauges the importance of the task. He explains that to us above all, to keep some kind of digital reproduction in 3D on the samples, the team starts with tomography.”It is the same as a medical scanner“.
The first analyzes are performed by eyes first. The first clues that Cedric Mullis explained to us:This block comes from a small gap between two main stones for the arch of the nave. Who fell into fire. It teaches us a lot of things. First of all, we have the thickness of the mortar joint less than 1 cm. This makes it possible to understand what the mortar dose was in relation to the stones at this precise location.“For Cedric Mullis, we can also figure out which tool was used to cut the stone.”It behaves somewhat negatively compared to what we no longer see. There are a lot of small teeth, which correspond to the passage of a tool called a bretture, which was used widely Stone cutEspecially at the end of the twelfth century throughout the thirteenth century, in Ile-de-France in particularWe can also see a cross. The most reliable hypothesis is the hypothesis of the sign which undoubtedly indicates the direction the stone should have taken while breaking its arc.
It’s an 800-year-old mortar
For the team, it’s all about answering several questions. Like this: What recipe is used for the mortar? A mortar is a type of putty that is used as a glue to hold stones together. It is usually composed of sand, water and binder materials. Is the technique used in the Middle Ages in Notre Dame special? Another question for the team of scientists. Researchers from the Jean Lamour Institute, with the help of their colleagues from GeoRessources Lab, He will endeavor to travel to the heart of the matter using various tools. “She is 800 years old. Samples are collected from the fallen blocks. And they were hit by fire and water to extinguish the fireJean-Michel Micheling explains. Analysis of “thin sections”, a geology and rock technique (a thin section of a rocky portion that allows light to pass through most of its opaque minerals), made by GeoRessources Lab, provides preliminary information on the composition of the materials that make up the slurry.
There’s another step a little further, in another lab at the Jean Lamour Institute. Here, we find tools called x-ray diffractometers, which are used to describe crystals. “The most important in FrancePascal Pollitt, head of the laboratory, and research engineer at the Jean Lamour Institute (CNRS / University of Lorraine) explains. A small sample of slurry is first converted into powder before being put into the machine.
Notre-Dame is an exceptional site for which we also put exceptional resources.
The final step takes us deep into the matter and into the basements of the Jean Lamour Institute. Thanks to an electron microscope with atomic resolution, we come down to infinitely smaller scale. Here, mortar pores, quartz grains and calcareous nodules show traces of an admixture likely to have been made in the 12th century. At this level, scientists are looking for “Needle in a haystackJean-Michel Micheling and Melanie, study engineer at the Jean Lamour Institute who specializes in microscopy, are looking for uniqueness, something that must be verified in all samples analyzed … “the chalice”! Which represents a type of signature. “Notre-Dame is an exceptional site in which we also invest exceptional resources. We are looking for fine details with this electron microscope. Other techniques are necessary to really find a lot. We may seek transient signatures that can only be found in certain mortars.“
“The problem is, this happens on a very small scale. We can spend weeks on just one sample. This is one of the difficulties with this technology. You have to try to have something as representative as possible. On a few cubic microns of material, try to distinguish what background noise is, and what is or could be exciting for our investigation“.
The first results seemed to indicate that these slurries were somewhat homogeneous and that the joints used were particularly thin. “The architects responsible for managing the project and who will lead the work of the cathedral will have access to this data. The idea is to be as close as possible to the materials and technologies used at the time.“Jean-Michel Micheling concludes,
An investigation continues at the Jean Lamour Institute to try to reconstruct the original recipe for the 800-year-old mortar. The team continues to hope for a distinctive feature of the mortar.
The team has until summer time to come to their conclusions. President Emmanuel Macron has just confirmed that the deadlines for the reopening of Notre Dame de Paris will be met to the public in 2024.