In this paper a new approach to quantitative Laser-Induced Breakdown Spectroscopy (LIBS) analysis of silicate rocks is presented. The method is adapted from the Franzini and Leoni algorithm, a method ...widely used in X-Ray Fluorescence analysis for correcting the matrix effects in the determination of the composition of geological materials. To illustrate the features of the new method proposed, nine elements were quantified in 19 geological standards by building linear univariate calibration curves, linear multivariate calibration surfaces (PLS) and using Artificial Neural Networks. The results were then compared with the predictions derived from the application of the algorithm here proposed. It was found that the Franzini and Leoni approach gives results much more precise than linear uni- and multivariate approaches, and comparable with the ones derived from the application of Artificial Neural Networks. A definite advantage of the proposed approach is the possibility of building multivariate non-linear calibration surfaces using linear optimization algorithms, a feature which makes the application of the Franzini and Leoni method in LIBS analysis much simpler (and controllable) with respect to the algorithms based on Artificial Neural Networks.
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•The Franzini-Leoni method, used in XRF analysis, is adapted to LIBS.•19 geological samples are analyzed with this method.•The method is compared with linear/non-linear univariate and multivariate approaches.•The non-linear model can be obtained using linear optimization algorithms.
Abstract
Within a major framework of studies around artificial weathering and its effects on different lithotypes, in this work we study the effects of thermal stresses after artificial thermal decay ...on different types of stones used in historical buildings: a sandstone, a calcarenite and a marble. The sandstone belongs to the so called “Macigno” Formation and mainly outcrops along the northern Apennine (North Western Tuscany) and it has been widely used around Tuscany for building purposes (e.g., in Florence, Lucca, Pisa, Pistoia, etc.); the analysed calcarenite (Gravina) comes from the surrounding of Matera Town and has been deeply used for the construction of the ancient buildings of the town itself; and the marble comes from the Carrara marble district (Northern Tuscany), a highly used stone throughout the centuries as ornamental stone. All these types of stone for their physical and mechanical properties, and aesthetic appearance, have been extensively used as both ornamental stones and as construction materials. To reproduce a plausible effect of natural thermal decay of the stones due to day-to-night and season-to-season fluctuations, we subjected the samples to artificial thermal decay. We carried out different thermal cycles on the samples by using a stove at 150°C and a muffle furnace at 300°C and 450°C. We analysed the physical and mechanical properties before and after each cycle to compare and evaluate the effects of thermal stresses on the stones. Among the different analyses: mass and volume measurements, water absorption tests, mercury intrusion porosimetry, thin-section observations and determination of chromatic alterations through image analysis and Munsell charts method. It was then possible to evaluate the influence of both mineralogy and microstructures on thermal decay of the studied stones (variations in fabric and modifications on physical and mechanical properties).
Abstract
Often when we approach the study of lithologies coming from the urban environment, but in general, even from any other environment, be it a quarry, a mine, an outcrop of our interest, the ...first study we carry out is the one in reflected-light optical-microscopy. Reflected-light microscopy in respect to transmitted-light microscopy requires minimal sample preparation, having to polish a single surface and without the need to thin the samples to allow light to pass through them. It may be useful, already in the first analysis, to try to produce quantitative data on what we are observing. A further advantage of reflected light in an urban environment is that of being able to observe and describe the formation or interaction between opaque minerals and the environment. Information that we lose by passing directly to the transmitted light. The information that can be useful to us and that we can obtain are the relative porosity of the sample, the texture (when easily recognizable in reflected light), the maximum size and shape of the edges of the grains. To all this is added the relationship between the areas of the different crystallites identified and the possible background mass, which cannot be solved on the observation scale. When we are dealing with many samples, we do not always have the time to be able to study individually sample by sample through images, so we resort to the use of image analysis tools for image segmentation and analysis. Among these, the main thresholding method with the Otsu method, the segmentation with the k averages algorithm, and, finally, a neural network of the SOM type. In this short work, we will review the main methods of image segmentation plus an innovative method developed by our group, highlighting its strengths and weaknesses.
In this article, we compare two analytical methods that have been recently proposed: the columnar density Saha–Boltzmann plot method of Cristoforetti and Tognoni (Cristoforetti, G.; Tognoni, E. ...Spectrochim. Acta, Part B, 2013, 79–80, 63–71) and the C-sigma model of Aragon and Aguilera (Aragon, C.; Aguilera, J. A. J. Quant. Spectrosc. Radiat. Trans. 2014, 149, 90–102). Both methods are based on the exploitation of self-absorbed lines for the characterization of plasmas in laser-induced breakdown spectroscopy experiments. However, although the two methods can be safely applied in many cases, their usefulness is limited in many practical cases of interest because of the intrinsic constraints of the used plasma model or because of the complexity of the numerical treatment. The two methods are presented here and critically discussed. Finally, an extended C-sigma approach is proposed to merge the advantages of the two methods, overcoming their intrinsic limitations and simplifying the numerical treatment.
The identification of both the organic and inorganic fraction of dyes and pigments is fundamental for their complete characterization and to assess the technologies used in their production.
In this ...work, the feasibility of determining metallic elements used as mordant for dyed textiles was tested using Laser-Induced Breakdown Spectrometry (LIBS) in combination with liquid micro-extraction. Both reference laboratory-dyed and historic textiles were analysed in this study. Samples were first analysed without any preparation. Then, the chromophores-containing molecules were separated using a sample preparation procedure based on aqueous hydrolysis, and analysed by high-pressure liquid chromatography coupled with a diode array detector. The same extracts, containing also the inorganic fraction, were analysed by Surface-Enhanced Laser-Induced Breakdown Spectroscopy (SENLIBS) after drying on a solid substrate.
Compared to the direct analysis, the SENLIBS method improved the sensitivity of the measurements. The procedure presented here allowed for the characterization of both organic and inorganic fraction of a single textile micro sample, thus avoiding further sampling.
•Combination of liquid analysis with surface enhanced LIBS.•Elemental analysis in textile samples after micro-extraction procedure.•Organic fraction characterized by HPLC-DAD.•This method improved the sensitivity of LIBS in liquids analysis.
•The dye formulation behind daylight fluorescent pigment was investigated.•Silver nanorods were used as SERS substrates.•TLC-SERS proved to be necessary to solve the complex composition of DFP.•The ...spectroscopic data will be implemented by building a database of DFP.
Raman and surface enhanced Raman spectroscopy (SERS) are established techniques allowing for fast and sensitive identification of dyes and pigments. To date, Raman has only limitedly been applied to the identification of daylight fluorescent pigments, despite this modern class of materials has been adopted by several significant artists (e.g. Frank Stella, Peter Halley, Andy Warhol, and Keith Haring).
In this study, seven commercial daylight fluorescent pigments from Radiant were investigated by Raman and SERS spectroscopy. A new type of silver colloid, consisting mainly of rod-like silver nanostructures guaranteeing a high SERS enhancement, has been employed here for the first time in cultural heritage studies.
As the number of fluorescent dyes suitable for the manufacturing of daylight fluorescent pigments is limited, these materials are often constituted by a mixture of dyes. Since SERS is not able to physically separate multiple dyes in mixtures, to reveal the complex composition of these materials the coupling of SERS with a separation technique proved to be mandatory. Thin-layer chromatography, being a cost-effective and fast procedure, was chosen for this purpose. The identification of each component was made possible by the comparison of SERS spectra from standard fluorescent dyes, thus increasing the available SERS database for modern materials.
Lastly, the analytical protocol was applied to a modern artwork called “Rosso verde nero”, made in 1968 by the Italian artist Carla Accardi, who used to paint on plastic surfaces with fluorescent colours.
The laser-induced breakdown spectroscopy (LIBS) technique was used for analyzing the composition of an ancient Roman mortar (5th century A.D.), exploiting an experimental setup which allows the ...determination of the compositions of binder and aggregate in few minutes, without the need for sample treatment. Four thousand LIBS spectra were acquired from an area of 10 mm2, with a 50 µm lateral resolution. The elements of interest in the mortar sample (H, C, O, Na, Mg, Al, Si, K, Ca, Ti, Mn, Fe) were detected and mapped. The collected data graphically shown as compositional images were interpreted using different statistical approaches for the determination of the chemical composition of the binder and aggregate fraction. The methods of false color imaging, blind separation, and self-organizing maps were applied and their results are discussed in this paper. In particular, the method based on the use of self-organizing maps gives well interpretable results in very short times, without any reduction in the dimensionality of the system.
Archeological mortars are often composed of highly inhomogeneous materials and detailed analysis in most cases can be quite difficult. In this work, a Laser-Induced Breakdown Spectroscopy (LIBS) ...equipment with microscopic-scale spatial resolution was used to image the distribution of elements on real archeological samples of mortars and construction material used in the foundations of the Smederevo Fortress (Republic of Serbia). A double-pulse Nd:YAG at the fundamental wavelength (λ = 1064 nm) and a CCD spectrometer coupled with a commercial microscope were used to generate the plasma and acquire the LIBS spectra. Thanks to the combined use of an unsupervised clustering algorithm and the calibration-free procedure, the results obtained show that it is possible to obtain a good discrimination between materials of different composition, allowing a quick classification for further mineral-petrographic investigations.
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•Elementary imaging on highly inhomogeneous samples.•LIBS mapping application on historical mortar samples.•Performed CF-LIBS analysis on average spectrum, to estimate the elemental composition of the different zones of the sample.
This paper deals with the stones used as building materials in the centre of Pisa during the Middle Age. Most of the stones are quarried from the nearby mountains, Monte Pisano and Monti d’Oltre ...Serchio, but there are also other ones, coming from Apuan Alps, Elba Island, western Tuscan coast, and from other quarries opened in the Western Mediterranean area. Our goal is to enrich the classic concept of street photography by inserting, in an interpretative context, the analysis and the observation of the geoenvironment in which we are immersed, daily, for the journey home-office, home-school or just for a simple walk. The tools we have are the eyes, the light and an instrument: the camera. Five stops along a city route allow to describe the main types of stones that have been used to construct and ornate the buildings since the 10th and 11th centuries, when Pisa acquired its traditional fame as one of the four historical Maritime Republics of Italy. Monte Pisano marble is the most important stone in the medieval phase of construction of the city of Pisa, often used together with black limestones to give the typical decorative alternate bands, black and white, of the Pisan Romanesque style. Other types of stones were also used, such as Quartzites, Agnano breccia, Panchina, Macigno sandstone as well as Apuan marble, granitoid rocks from Elba Island and Sardinia, and some rocks from ancient quarries of the western Mediterranean area, such as precious marbles from Greece and Turkey.
3D multi-band/multi-spectral reconstruction is a technique, which allows the use of images taken in different spectral bands for the reconstruction of spectrally-resolved 3D models of paintings. In ...this work, we propose a procedure for constructing and comparing 3D multi-band models obtained starting from a variety of input data (RGB and IR images, UV-induced fluorescence images, etc.) and/or acquired with different instruments. The procedure has been tested on two case studies, with the aim to highlight the critical issues associated to the specificities of the subject and of the environmental constrains: a 14th century panel painting signed by Barnaba from Modena, preserved at the Museum of San Matteo in Pisa, Italy and a 15th century panel painting preserved at the Regional Gallery of Palazzo Bellomo in Syracuse, Italy. RGB, IR and UV–VIS fluorescence models obtained with a conventional digital camera (RGB and UV) and a multisband camera (IR) were realized and compared, for revealing differences at sub-millimeter level.
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