Vincent Detalle

Non destructive testing in situ, of works of art by stimulated infra-red thermography

This paper presents various examples of assistance to the restoration of mural paintings by infra-red photothermal radiometry. First, we present the experimental device implemented for the study. Then, we show the possibility to detect separation or air voids by this technique in various works of art as the Saint Christopher of the Campanna collection of Louvre, in the painted ceilings of the abbey of Savin Saint sur Gartempe (classified with the world heritage of UNESCO) and finally in the Cocteau frescoes of the vault Saint Pierre of Villefranche sur mer.

Approach of the measurement of thermal diffusivity of mural paintings by front face photothermal radiometry

This paper deals with the approach of the possibilities of the front face photothermal thermography to measure the longitudinal thermal diffusivity of a mural painting. We present at first the principle of the method of measure based on the use coupled of transformed integrals and thermal quadruples. We show then the feasibility of the method by means of numerical simulation. We present then the experimental device implemented for the study. We show finally, by means of the experimental study of a sample of plaster, which the photothermal method allows in a particular case, a good estimation of the parameter longitudinal thermal diffusivity. Within the framework of the assistance to restoration of mural painting, our laboratory works since about ten year on the detection of detachment and air pocket situated in frescoes. The front face photothermal thermography, has already allowed us to detect, in situ, detachment situated in the Saint Christopher of the “Campana” collection of “Louvre”, in walls painted of the church Saint Florentin of Bonnet, in ceilings painted of abbey of “Saint Savin sur Gartempe” (classified in the UNESCO world heritage) and finally in the frescoes Cocteau of the vault “Saint Pierre” of “Villefranche sur Mer” [1-3 ]. These qualitative studies being positive, they push us now to study the possibilities of the photothermal method in characterization of the defects. Later, the objective is to determine both the area of the defect but also the depth in which it is situated. For it we intend to proceed by an adjustment theory / experiment with the use of methods of inverse techniques of the type levenberg marquardt [4]. To feed the model evoked previously, it is necessary to know the thermophysical properties of the studied materials. Two solutions were offered to us: either appeal to bibliographical values that is to develop a method of measure of diffusivity usable in situ. For reasons of appropriate life of materials (ageing, presence of humidity, manufacturing processes, environment), it is the second solution that we chose to implement. To lead to these measures of diffusivity, we had even there two solutions: either take a sample of work of art or implement a classic method of measure of this thermophysical parameter (method flash [5]), or develop a useful method in situ and non-destructive for the studied mural painting. For reasons of good preservation of the works of art, it is this last option we chose to implement. The thickness of the couple coats - wall composing the mural painting being often of several tens centimeters, a measure of transverse thermal diffusivity is often impossible. We thus chose to develop a method of measure of longitudinal thermal diffusivity of the work of art. It is this method we present here. We present at first the principle of the method of measure, based on the use coupled of integral transformations and the quadrupole method [6]. We show then the feasibility of the method by means of numerical simulation. We present then the experimental device developed for the study. We show finally, the method gives access to a good estimation of the longitudinal diffusivity of a sample of plaster. 2. Principle of in situ measure of longitudinal thermal diffusivity

Mapping of defect structural micro-morphology in the documentation of conservation approaches

In this paper a study of fresco wallpaintings with the use of Digital Holographic Speckle Pattern Interferometry and Infrared Thermography is beeing presented. Fresco technical samples as well as mural paintings in the Abbey of St. Savin have beeing examined. The information provided by both techniques leads to valuable results concerning the state of the mural paintings and provides information for their restoration and further conservation.

Combination of interferometry and thermography data for cultural heritage structural diagnostic research

The demand for non destructive and non invasive structural diagnostic techniques able to perform on field remote structural evaluation of historical structures and works of art it faces an increased demand. The techniques must have some basic important characteristics The non destructivity, accuracy, repeatability, non physical contact, portability, resolution, broad range of applicability depending on the type of artwork and the question at hand, are all among the important requirements underlying the requirement for on-field structural diagnostics. In this respect there are two known techniques that have been developed at full to provide a suited structural diagnostic application in artwork conservation. The systems presented here but discussed in detail elsewhere are stimulated infrared thermography (SIRT) and digital holographic speckle pattern interferometry (DHSPI) the prior can be found n market at commercial devise level while the latter is at laboratory prototype level. The two systems are being exploited for their complimentary advantages and in this paper are used in combined testing on art related targets according to the above criteria to confirm the enhanced diagnostic information that their complimentary use provides. Results confirm the effectiveness of each technique alone and the combination of data of both techniques in the conservation field. Each system is first briefly described and examples are given with the aim to present the suitability and appropriateness for use in structural documentation analysis and reports. The experimental work is in laboratory work-in-progress focusing on the hybriding of data synthesis.