Antonio Sansonetti

Nd:YAG laser effects on inorganic pigments

Abstract The effects of a Q-switched Nd:YAG laser irradiation on a group of supports, painted with six different inorganic pigments, was investigated. The pigments were chosen from among the most utilized on painted historical surfaces: red ochre, yellow ochre, chromium green, ultramarine azure, white chalk and carbon black, and they were distempered with two binders – linseed oil and gypsum – on primed wood panels. The pigments were characterized by means of X-ray diffraction and Fourier transform infrared spectroscopy. Chromatic characteristics, chemical composition and surface morphology of the painted layers were investigated before and after the laser irradiation. Three different fluences were used to detect the correlation between laser parameters and changes in painting layer characteristics.

Optical and spectroscopic tools for evaluating Er:YAG laser removal of shellac varnish

Abstract We report on tests to remove naturally and artificially aged shellac varnish by laser and traditional chemical cleaning from the substrates of mural paintings. Optical tools were used for the evaluation of cleaning processes, in particular laser microprofilometry to assess the changes in the surface morphology and time-domain confocal optical coherence tomography (OCT) to evaluate varnish thickness. The cleaning assessment was integrated with molecular characterization provided by portable Fourier transform infrared spectroscopy operating in reflectance mode, and colorimetric measurements. This complete analytical approach led to optimized laser-based cleaning tests at 1.9 and 2.6 J/cm2 in the presence of isopropanol, which ensured controllable and safe partial removal of shellac varnish without alteration to the substrate morphology.

Evaluation and monitoring of water diffusion into stone porous materials by means of innovative IR thermography techniques

Abstract This paper shows the application of two innovative infrared thermography (IRT) methods for the evaluation of water transport phenomena through the outer layers of porous stone materials. An infrared camera measured: (a) the moisture stain due to the water absorption after having spilled a drop on the stone surface and (b) the ”moisture ring” around the damp surface, after the contact between a soaked round sponge and the stone surface. The time of spreading and the geometric shape of the damped area depend on the porosity of the stone material and are useful to characterize the physical stone features. In addition, monitoring the evolution of the moisture ring by IRT allows implementing and optimize the data coming from protocols of water repellent products with data coming from the “contact sponge measures”. Moreover, moisture ring test links IRT and laboratory tests characterizing the transport phenomena of liquid and water vapour in porous building materials. Thirty specimens of marble, calcarenite and sandstone were tested with steady methods (dry index and water absorption by capillarity), that validated the data provided by the two innovative IRT techniques.

Laser cleaning of a nineteenth-century bronze sculpture: In situ multi-analytical evaluation

Abstract Laser cleaning of bronze artefacts is a very promising conservation approach and its wider distribution would benefit from further studies of its advantages and drawbacks. Some important references are available, yet laser cleaning cannot be considered a traditional method for bronze surfaces. In this paper, we report on the evaluation of cleaning tests performed on an important statue of Napoleon, depicted as Mars the Peacemaker, cast by Righetti in 1811 after a model by Antonio Canova. The sculpture is exposed to the outdoor environment in the main courtyard of the Brera Gallery, Milan, Italy. An analytical survey of corrosion products was carried out using X-ray diffraction, micro-Fourier transform infrared spectroscopy (μFTIR), and μRaman spectroscopy; and scanning electron microscopy with energy-dispersive X-ray spectroscopy analysis was applied to cross-sections. The results showed the ubiquitous presence of brochantite Cu4(SO4)(OH)6. Antlerite Cu3SO4(OH)4 is also occasionally present. Residues of an past conservation treatment (Incralac®) and of proteins were detected by μFTIR. Laser cleaning tests were carried out with an El.En. Combo laser, both in long Q-switched and short free-running regimes. Evaluation of the effects of cleaning was carried out with a portable microscope and a reflectance colorimeter. Moreover, a portable FTIR spectrometer was used in order to evaluate the presence of coating residues and corrosion products after cleaning. Electrochemical impedance spectroscopy was used in situ on a selection of the tested areas in order to characterize the effect of laser cleaning on the rate of corrosion. A specially designed contact probe was used for measurements in the frequency range 100 kHz–10 mHz both before and after cleaning.

Evaluation by Laser Micro-Profilometry of Morphological Changes Induced on Stone Materials by Laser Cleaning

This work, aimed at quantifying the morphological variations induced by laser cleaning on stone materials, represents a very first attempt for a new quantitative means to reveal changes in stone surfaces. It is a three-dimensional survey carried out by means of laser micro-profilometry and completed by statistical data processing. The acquisition and successive computation is performed on small selected areas both before and after the cleaning process.

A multi-analytical approach for the characterization of wall painting materials on contemporary buildings

Samples from Keith Harings wall painting of the Necker Children Hospital in Paris were studied by a multi-analytical protocol. X-ray fluorescence (XRF), powder X-ray diffraction (XRDP), Electron microscope (SEM-EDS), Infrared and Raman spectroscopy (μ-FT-IR and μ-Raman) measurements were performed in order to characterize the materials and to identify the art technique used to produce this contemporary work. Materials from the mural suffered from severe detachments of materials and several fragments were found on the ground beneath. Some of these fragments, which were representative of the whole palette and stratigraphic sequence, were collected and studied. The fragments were sufficiently large to enable non-invasive measurements to be performed in order to characterize the materials. A comparison of the data of the techniques applied revealed that Harings palette was composed of organic pigments such as Naphtol red, phthalocyanine blue and green and Hansa yellow, in accordance with those used previously by the artist in other painted murals.

MOdihMA at Sforza Castle in Milano: Innovative Techniques for MOisture Detection in Historical Masonry

The research line MOdihMA (MOisture detection in historical MAsonry) proposes to improve the innovative techniques recently developed to measure different parameters related to water content in masonry, that has an important role in the damage of historical buildings. The first objective of this project is to compare the effectiveness of the different methods in understanding how the quantitative data obtained are directly related to water content. The second objective of the MOdhiMa project is to compare the ability of the different techniques to map water as a function of its location and depth within the masonry structure, both on macro and micro-scale. A selection of these innovative techniques recently had an application on the “Sala delle Asse” in the Sforza Castle in Milan. The hall is famous for the decoration of the vault and the monochrome on the northwest wall, attributed to Leonardo. Recently Milano Municipality defined the plan of diagnostics for detecting the causes of the increasing damage on the painting and the poor conditions of conservation of the vault. Unilateral NMR, SUSI, IR Thermography, gravimetric and chemical tests were applied for mapping the moisture distribution in the bottom of the northwest wall. The comparison with the results of the standardized techniques confirmed the low moisture content distributed in the masonry.

Evaluation of Moisture Transfer to Improve the Conservation of Tiles Finishing Facades

The research of methodologies and tools to improve the durability of building components has the aim to find out the strategies to increase the service life, minimizing the environmental impacts. The paper refers on clinker facades, especially after the repairs of mortars due to severe damages. The authors achieved on-site investigations on a prominent study case in Leonardo Campus, at Politecnico di Milano, and laboratory tests to study the interaction between moisture and cement mortars, the decay effects, and the protective treatments to improve the mortar durability. The research sharpens the methods for the evaluation of water absorption and moisture transfer in external building components and proposes possible strategies of intervention. The methodology focuses on the characterization of the water behavior in mortars by different tests, the experiments in laboratory on mortars samples, to study the hygroscopic and capillarity absorption properties, and on site, through visual analysis and nondestructive techniques. The researchers studied a water-repellent protective treatment to apply on the finishing surface and evaluated it in terms of water-repellent efficacy, compatibility with the substrate, vapor permeability, and color stability. The investigations provide input data, useful for simulating the moisture transfer, validating the experimentations, and modeling the physical mechanisms, which occur on the facade. In addition, the method analyses also the optical characteristics of the surface, with the aim to detect any change due to the application of further protective treatments and for aging process.