Marco Giamello

Determination of damage thresholds to prevent side effects in laser cleaning of pliocene sandstone of Siena

Abstract The present work reports a basic investigation aimed at optimizing laser cleaning interventions on pliocene sandstone of Siena. Irradiation trials were performed with a short free running Nd:YAG laser, on quarry samples and on samples from Palazzo Spannocchi presenting black crust. The physical parameterization associated with a detailed petrographic and mineralogic diagnostics of the induced effects, allowed the irradiation thresholds for damage phenomena to be derived and their nature understood. The experimental results reported here allow the definition of the best irradiation conditions and the laser parameter ranges for a safe and controlled black crust removal from pliocene sandstone.

Laser cleaning methodologies for stone façades and monuments: laboratory analyses on lithotypes of Siena architecture

Abstract The present study was conceived for an evaluation of the effectiveness of laser cleaning techniques applied to samples collected from numerous monumental buildings in the city of Siena (Palazzo Pubblico, Cappella di Piazza, Baptistery, Logge del Papa and Palazzo Spannocchi). All the characteristic lithotypes of Sienese architecture are represented: Montagnola Senese marble, Cavernous limestone, Pliocene sandstone and Red Ammonitic limestone. The tests were devised so as to have the widest variability of situations in relation to the colour and composition of the lithotypes, the state of deterioration of the samples and the level at which to stop the cleaning. The tests were preceded and followed by detailed petrographic analyses. In the introduction to the work, we underline the importance of an accurate reconstruction of the stratigraphy of the external horizon of deterioration of the stone for an appropriate choice of the cleaning intervention; the potential advantages of laser techniques are consequently further emphasized.

Application of a new laser cleaning procedure to the mausoleum of Theodoric

Abstract Within the conservation programme of the mausoleum of Theodoric, located in Ravenna, Italy, we applied a new cleaning procedure based on the use of a recently developed Nd:YAG laser system, suitably equipped in this case with long optical fibre cables for the transmission of laser radiation to work sites on the facade. The intervention of the laser technique was required to complete the cleaning of a decoration surrounding the monolithic dome, after conventional cleaning methods had been applied with unsatisfactory results. Preliminary laboratory analyses on stone samples collected from the dome and subjected to laser treatment indicated that this technique was effective and could fully preserve the lime–Ca oxalate film existing below the thick layer of black crusts. Before starting the operative phase on the mausoleum, it was necessary to solve the practical problem of keeping free access to the monument during cleaning operations, which hindered the location of the laser in close proximity to the sites to be cleaned. This was achieved by preparing long fibre cables (up to 50 m) which permitted the successful completion of the cleaning while leaving the laser body far away from the dome.

Laser cleaning of stone by different laser pulse duration and wavelength

The present work focuses on the main phenomenological features of stone cleaning by lasers. These are the removal rate, cleaning degree, and chromatic appearance of the treated surface associated with different conservation problems and laser parameters. A set of three different outdoor stone conservation problems were investigated here. The measurement of the ablation rates were carried out on encrusted stone artifacts and two sets of standards in order to derive general behaviors through repeatable measurements. The analysis of the irradiation tests provided quantification of the different efficiencies, cleaning degree, and chromatic appearances associated with the fundamental harmonic of Q-switching, long Q-switching, and short free-running Nd:YAG lasers (1064 nm), as well as with the second harmonic of Q-switching sources (532 nm).

Phenomenological Characterisation of Stone Cleaning by Different Laser Pulse Duration and Wavelength

The present work focuses on the main phenomenological features of stone cleaning by lasers. They are the removal rate, degree of cleaning, and chromatic appearance of the treated surface associated with different conservation problems and laser parameters. A set of three different outdoor stone conservation problems were investigated here. The measurement of the ablation rates were carried out on encrusted stone artefacts and two sets of prepared samples in order to derive general behaviour through repeatable measurements. The analysis of the irradiation tests provided a quantification of the different efficiencies, degree of cleaning, and chromatic appearances associated with the fundamental harmonic of Q-switching, long Q-switching, and short free running Nd:YAG lasers (1,064 nm), as well as with the second harmonic of Q-switching sources (532 nm).

Archaeometric study of natural hydraulic mortars: the case of the Late Roman Villa dell’Oratorio (Florence, Italy).

This paper shows the results of a multidisciplinary study carried out on the mortars from the Late Roman Villa dell’Oratorio (fourth-sixth ad), an aristocratic mansion built in the lower Valdarno (Florence, Italy). Thirty-one bedding mortar and plaster samples were analysed through optical microscopy, thermogravimetric analysis, X-ray powder diffraction and scanning electron microscopy with energy-dispersive X-ray spectroscopy for determining the chemical, mineralogical and petrographic characteristics, while their main physical properties were measured by geotechnical procedures. The collected data indicates that the analysed mortars are made up of very fine to coarse river sand aggregate mixed with white to yellowish-white natural hydraulic lime binder mainly consisting of mixtures of prevailing calcite and hydraulic compounds. With regard to the origin of the raw materials, the aggregates were recognized to be selected Arno river sands, and the binders are the burning product of a local marly limestone (ex Alberese). Therefore, the mortars of the Late Roman Villa dell’Oratorio are one of the first uses of natural hydraulic lime in the lower Valdarno.

Grancia of Cuna: From the Complexity of the Historical Building to a Composed Knowledge for the Project

First results on the knowledge of the stratified complex of Grancia of Cuna derived from interdisciplinary researches and from works of preservation in progress. Methods of analysis and interrelation of the contributions derived from various professionals involved in the project of conservation and re-functionality.

The Medieval Grange of Cuna – Siena (Italy)- Interdisciplinary Studies on Masonry Structures

A team of specialist in different subject worked together with a multidisciplinary approach for the conservation of the complex of the Grange of Cuna, the administrative and storage center of the bigger farm of Santa Maria della Scala Hospital in Siena (Italy) in Middle Ages. Laser scanner surveys, archival and bibliographic researches, stratigraphic surveys, structural surveys were carried on and studied by the members of the team on the complex of 167 rooms. The results obtained by specialist approach was frequently discussed and compared in order to obtain a deeper knowledge of the complex of buildings. Structural engineer studies concerned the identification of different typologies of masonry and the structural diagnostics to mechanical characterization. Double flat jack and sonic inspection were performed on tapial adobe, brick masonry with lime and mud mortar.

Measuring weathering and nanoparticle coating impact on surface roughness of natural stones

ABSTRACT The surface texture of a stone represents a sensitive parameter in evaluating its conservation state. In monuments and sculptures, in fact, external agents continuously alter the appearance of stones, determining peculiar weathering patterns and modifying properties such as retention of water and particles, interaction with light, color, and finishing. The application of protective coatings also determines changes in surface appearance of a stone, usually evaluated and monitored by color change tests. Surface metrology methods offer the possibility to quantify these changes, evaluating the impact of external agents (natural, i.e. weathering, and artificially, i.e. protective coatings) on natural stones. In this research, we demonstrate the potential of surface areal measurements in describing the evolution of weathering processes and the effects of protective treatments on porous stone materials. The obtained results suggest that the extent of the modifications is related to the scale of observation (small- vs. large-scale undulations, i.e. roughness and waviness, respectively), with an overall increase of surface roughness as the weathering proceeds. Unexpectedly, coatings based on nanoparticle dispersions increase the topographic height parameters, due to the absence of a homogeneous film.

Production of the Roman Cement in Italy: characterization of a raw material used in Tuscany between 19th and 20th century and its comparison with a commercialized French stone material

ABSTRACT An experimental approach in order to investigate the possibility that some Italian limestones were used for the production of Roman Cement is proposed. Three types of Pietra Alberese, a marly limestone used since Roman times for the production of “lime” in Tuscany (Italy), were selected. By burning of these stones, specimens of binders were realized. The characteristics of these binders were compared with the binder obtained by burning a French marly limestone commercially used for the production of Roman Cement. All samples of carbonate stones were preliminarily characterized from the chemical, mineralogical, and petrographic point of view. The colorimetric coordinates were measured on both rock samples and hardened binder samples. The analysis carried out shows that Pietra Alberese with an high content of clay minerals develops a similar microstructure with respect to that developed by the French marly limestone used for the production of Roman Cement.