Revealing the iron skeleton of Notre-Dame de Paris. Methodologies and issues of archaeological and analytical investigations following the blaze

The fire at Notre-Dame de Paris led to the discovery of several series of previously unknown iron armatures, which were systematically recorded. Amongst them, several iron staples from the top of the eaves walls, lead crest reinforcements and a sample of the tie rods used in the choir in the 19th century were analysed by metallography and tensile tests in order to determine their nature and mechanical characteristics. These results can be put into perspective with previous studies on such monuments. The chemical analysis with SEM-EDS of the slag inclusions contained in the matrix of these ferrous alloys makes it possible to determine the technical processes used for their production throughout the construction and restoration of the building, highlighting several differences depending on the typologies of the iron armatures. This information is complemented by a series of radiocarbon dates currently being carried out to better understand the periods of use of these ferrous reinforcements. When compared with those of other materials, these dates could be used to recalibrate the phasing of the building.