National Heritage
Physicochemical analyses have become essential to understanding restoration projects.
Among the addressed issues: revelation of original decoration, identification of different phases of polychromy, extent of previous restoration work and better understanding of visible alterations.
A Scientific Database for Conservators-Restorers of Historic Monuments
CESAAR’s empirical approach is a real asset, continually enriching scientific knowledge of the various techniques used in a different periods and regions.
The acknowledged wealth of this reference base is an indispensable tool for most conservators-restorers of Historic Monuments.
CESAAR laboratory offers a range of technological resources enabling it to handle the full range of analysis services dedicated to Historic Monuments studies:
- Characterisation of materials
- Studies of weathering processes
- Determination of soluble anions and cations using ion chromatography
- Petrophysical tests (hardness measurements, sound wave propagation speed, etc.)
Discoloration of smalt on the surface of a wall paint sample- Notre-Dame de Chartres Cathedral. Chromatic alteration of the pigment resulting in potassium leaching from the periphery of the pigment particles (arrows), through the reaction of the alkaline elements constitutive of the glass (smalt: potassium glass tinted blue by cobalt oxides) with the fatty acids in the paint’s oil binder.
Stratigraphic Studies are crucial to understanding the decorations
The analysis is based on micro-samples of polychromy. The original colours and painting techniques are revealed, and any repaints and restorations are identified.
Samples are embedded in epoxy resin in order to perform microsection perpendicular to their surface. The microsection is examined under optical microscopy to identify the stratigraphy and pigment particles in each layer.
Stratigraphic section of a painting sample from an altarpiece, observed using optical microscopy (reflected and polarised light). Evidence of a succession of twelve decors. Original red decor from the 18th century (arrows).
Scanning electron microscopy (SEM) coupled with energy dispersive X-ray element analysis (EDX) allow then identification of the different phases of polychromy and characterisation of the mineral and metallic components (pigments, gilding, bronzine and mineral fillers) for each layer.
Organic pigments are studied using Raman spectroscopy.
Organic compounds (binders, glues, waxes, resins, lacquers, etc.) are analysed layer by layer using Fourier transform infrared micro-spectrophotometry.
Scientific Collaboration with Conservators-Restorers of National Heritage
The application of all part of these different scientific approaches depends on the question posed by the restorer-conservator.
The granularity of the scientific response depends on the question posed in the specific context of a restoration project.