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The photoreduction of aqueous Ag+ to silver nanoparticles (AgNPs) on a substrate was studied aiming at the application of surface-enhanced Raman scattering (SERS) technique to the sensitive analysis of organic colorants directly on artworks. In particular, the presence of the synthetic dyes methyl violet (BV1) and fuchsine (BV14), in both standard and historical wool fibers, was analyzed. Scanning electron microscopy was employed to study the morphology and distribution of the NPs obtained on the fiber. We have carried out an investigation of the influence of several factors on the morphology of NPs: excitation wavelength, substrate, laser power and laser irradiation time. The resulting materials were analyzed at different laser wavelengths in order to evaluate the application range of the probe laser after the NPs formation. SERS spectra of the BV1 and BV14 dyes on the fiber were obtained and compared with those obtained in suspended conventional AgNPs, in order to deduce the possible influence of the wool substrate on the Raman spectra. SERS spectra were analyzed considering the possible resonance Raman processes. Bands attributed to the protein substrate were also identified. The main goal of this work was to assess and optimize a general method of analysis of organic dyes on natural fibers based on the direct preparation of AgNPs by laser SERS technique. Copyright © 2017 John Wiley & Sons, Ltd.

In the field of applied researches in heritage science, the use of multivariate approach is still quite limited and often chemometric results obtained are often underinterpreted. Within this scenario, the present paper is aimed at disseminating the use of suitable multivariate methodologies and proposes a procedural workflow applied on a representative group of case studies, of considerable importance for conservation purposes, as a sort of guideline on the processing and on the interpretation of this FTIR data. Initially, principal component analysis (PCA) is performed and the score values are converted into chemical maps. Successively, the brushing approach is applied, demonstrating its usefulness for a deep understanding of the relationships between the multivariate map and PC score space, as well as for the identification of the spectral bands mainly involved in the definition of each area localised within the score maps.

InthispapersomecoloredframescomingfromtheverypopularcinematographicfilmSardinianDrummerBoy,datingbacktothebeginning of the XX century, were analyzed. The presence in the emulsion of silver nanoparticles (AgNPs), which are formedthanks to the impression–development mechanism, confers to the cinematographic film the characteristic of being an efficientSurface Enhancement Raman Spectroscopy (SERS) substrate. This peculiarity makes it possible to investigate, in a non-invasiveway, the nature of the film components, such as the dyes used for the coloring process. In particular, Raman analyses allowedthe unambiguous identification of the dyes used in tinted frames, i.e. tartrazine and safranin, in which the colorant is absorbedby the gelatin, and intoned frames, i.e.Rhodamine B, wherethe dyeisfixed thankstothe formationofaninsolublespecies withAgIobtainedbyconversionofmetallicsilver.Thissecondcaseisofparticularinteresttoevaluatethepossibilitytoidentifythedyeeven when it is present as a silver iodide derivative. For this purpose an AgI-colorant derivative has been prepared and its SERSspectrum compared with that obtained on the film sheet. Copyright © 2015 John Wiley & Sons, Ltd.Additional supporting information may be found in the online version of this article at the publisher’s web site.Keywords: cinematographic film; tinting; toning; SERS; dyes

The present research is focused on the setting up of an advanced analytical system for the detection of synthetic dyes. The system is based on the combination of an innovative thin layer chromatography (TLC) plate coupled with enhanced infrared (MU-ATR, metal underlayer attenuated total reflection) and Surface Enhanced Raman (SERS) spectroscopy. In particular, a TLC plate made of silver iodide (AgI) applied onto a gold coated glass slide (AgI@Au) is proposed as an efficient stationary phase for the separation of dyes mixtures. The separated dyes are then identified by means of both enhanced FTIR and SERS, performed directly on the same eluted spots. The use of a mid-IR transparent inorganic salt as stationary phase coupled with the underneath gold layer avoids spectral interferences, enhancing the signal obtained from ATR analyses. At the same time, SERS spectra can be recorded as the TLC plate may act as a SERS active substrate due to the photoreduction of AgI to metallic Ag caused by the exposure to the laser during the Raman analysis. Different mixtures of synthetic dyes of known composition, widely used in dyeing processes, have been tested and the method resulted to be effective in identifying trace amounts in the order of tens nanograms. Moreover, the method has been further evaluated on a real case study represented by dyes extracted from dyed wool.

The identification of organic dyes is a challenging task in all the fields such as the forensic and conservation sciences, especially in cases where the amount of sample is extremely small. In this paper we propose a new enhanced FTIR method (MU-ATR metal underlayer ATR spectroscopy), which we believe is the first of its kind, for the analysis of a few ng of dyes. With this method, dyed fiber micro-extracts can be analyzed using a commercial FTIR microscope with a fixed incident angle, obtaining the same separation between the different classes of dyes investigated as we obtained analyzing pure dyes in transmission mode. Moreover, the new enhancement method has been validated on a real sample dated back to the 1893, showing how it can be promising for the analysis of trace amounts of organic substances in artistic samples such as dyes in paintings or textiles, varnishes and organic residues on archaeological objects.

none 8 si To study degradation processes occurring on painting materials, the use of high-resolution micro-analytical techniques is highly requested since it provides a detailed identification and localisation of both the original and deteriorated ingredients. Among the various pigments recently studied, the characterisation of verdigris has received a major interest. This pigment has not a unique chemical formula, but its composition depends on the recipe employed for its manufacturing. Moreover, verdigris paints are not stable and are subject to a colour change from blue-green to green, which occurs in the first few months after the application. In this paper, we focused our attention on the use of ATR-FTIR mapping as a useful method to identify verdigris secondary products and pathways. Several mock-ups and real samples have been analysed, and the correlation among the detected compounds and their spatial location, obtained by the application of ATR-FTIR microscopy in mapping mode, allowed formulating some hypotheses on the degradation pattern of verdigris, which may feed the discussion on the transformation and stability of this pigment. From an analytical point of view, we showed how FTIR mapping approaches may be extremely useful both for the identification of compounds in complex matrix in which single spectra may limit the exhaustive characterisations due to bands overlapping and for the study of degradation pathways by taking into consideration the relative distribution of degradation products. Prati, S; Bonacini, I.; Sciutto, G.; Genty-Vincent, A.; Cotte, M.; Eveno, M.; Menu, M.; Mazzeo, R. Prati, S; Bonacini, I.; Sciutto, G.; Genty-Vincent, A.; Cotte, M.; Eveno, M.; Menu, M.; Mazzeo, R.

We present an overview of recent advances in the application of Fourier Transform Infrared (FTIR) microscopy for analysis of complex, multicomponent, and multilayer samples such as those typically encountered in the field of heritage materials. This technique is particularly useful since it allows identification and localization of both organic and inorganic (if IR active) compounds. New improvements have been possible thanks to the introduction of ad hoc sample preparation methods to obtain either thin or cross sections that allow both avoidance of contamination from organic embedding resin and improvement of the quality of the acquired spectra. Moreover, integrated use of spectra registered in the near-infrared (NIR) and mid-infrared (MIR) regions allows better comprehension of cross section composition. Data interpretation has been improved thanks to the development of chemometric methods for elaboration of hyperspectral data. A new and very promising field is the development of enhanced FTIR methods for detection of trace components in microextracts. These systems, allowing detection of extractable organic compounds from about 0.1 mg of sample, will be extremely useful in the future for analysis of natural and synthetic colorants, varnishes extracted, for instance, from cotton swabs used during cleaning of paintings, and organic residues on archeological remains.