Optical Reflectance Spectroscopy Research Articles

Mechanism for Control of Laser‐Induced Stainless Steel Oxidation

AbstractThis paper presents the development of a model for Nd:YAG laser surface oxidation of 316L stainless steel. A full factorial design of experiments (DOE) are implemented to produce a model for the prediction of elemental composition and color. The elemental composition of the films produced where measured using an X‐ray photoelectron spectroscopic (XPS) and the color is measured using optical reflectance spectroscopy. Oxide layers produced have a Cr/Fe ratio in the range of 0.13–2.09, and highly controllable color variation via single‐pass laser process. The effect of the process parameters used such as power, frequency, and scan speed on laser‐induced oxides is examined with an aim to produce a model suitable for predictive control of the elemental composition and color of the oxide film. Surface morphology control via alteration of the laser power is an important factor for defining the resulting coloration. A new finding from this work is the discovery that within the range of laser surface processing parameters investigated, the molybdenum concentration is inversely proportional to the chromium concentration. This paper provides data required for control of 316L‐SS surface chemistry, and for the expansion of the current thermokinetic model to incorporate the mechanistic effect of molybdenum.

Formation of skyrmion phase in the Fe-Co-Si system by mechanochemical activation

Fe, Co and Si powders were exposed to mechanochemical activation by high-energy ball milling for 0, 2, 4, 8 and 12 h. The samples were subsequently characterized by Mössbauer spectroscopy, X-ray powder diffraction (XRPD), magnetic measurements and optical diffuse reflectance spectroscopy. The room temperature Mössbauer measurements were consistent with the occurrence of FeCo2Si and Fe0.5Co0.5Si crystalline phases. The low temperature Mössbauer spectra confirmed the absence of superparamagnetism up to 44 K in the milled system. XRPD patterns supported the phase sequence derived from Mössbauer spectroscopy. The coercive field was found to increase with the ball milling time (BMT). Zero-field-cooling-field-cooling (ZFC-FC) measurements performed at 200 Oe in the temperature range 5-300 K evidenced the transition to the skyrmion phase of the Fe0.5Co0.5Si material below the critical temperature of 44 K. The optical absorption in the UV-Vis-NIR region of the spectrum was found to increase with BMT.

The Dagulf Psalter (Austrian National Library Cod. 1861): A Multi-Analytical Approach to Study Inks, Dyes, and Pigments of this Early Carolingian Manuscript

Abstract The Dagulf Psalter is a precious Carolingian manuscript on calf parchment, dated to 793–795. Its unique and high historical value required a non-invasive, multi-analytical approach to gain insights into the material composition of gold and silver inks, pigments, and dyes used for writing and illuminations. Elemental mapping based on X-ray fluorescence analysis (XRF), Fibre Optics Reflectance Spectroscopy (FORS) measurements, and hyperspectral imaging (HSI) gave complementary information on colour media and their brilliant shades. Knowledge of the material composition of inks, dyes, and pigments is of crucial importance not only for art historical research, but also for the preservation of the manuscript, as it is known that among other factors, silver inks and some pigments can lead to deterioration of parchment supports. The purple dye orchil and blue indigo were used for painted backgrounds on the initial folios. Lapis lazuli was found in decorative frames on these folios. Orchil, indigo, and lapis lazuli also appear in decorations of small initials throughout the manuscript. Red lead, ochre, cinnabar, orpiment, and lead white were also found in various painted details. Gold and silver inks of high purity were identified. The proof of chlorine in the silver ink indicates the presence of corrosion products.

Temperature-dependent optical bandgap of TiO2 under the Anatase and Rutile phases

A crucial step in developing new and/or more efficient devices relies on the detailed knowledge of the properties of their main (elemental or combined) parts. The same applies to titanium dioxide TiO2 that forms the basis of today numerous applications whose performances are determined by the presence or relative amount of the Anatase (A-) and Rutile (R-) most common phases of TiO2. Whereas the basic structural characteristics of these two polymorphs are very well-established, some of their optical aspects still deserve attention. With these ideas in mind this work presents a comprehensive investigation of the optical bandgap Egap of TiO2 under the Anatase and Rutile phases. The study considered pure A-TiO2 and R-TiO2 samples in the form of powder, and optical reflectance and Raman spectroscopy in the 83–823 K temperature range. In addition to reliable Egap values the study explores their temperature-dependent Egap(T) behavior that is expected to assist future advancements in the field of TiO2-based materials and devices (thin films, interfaces, low-dimensional systems, and photocatalytic and solar cells, for example).

Highly efficient (V2O5)0.91Zn0.09 powdered catalyst for water organic pollutant elimination

(V2O5)1-x Znx powdered samples with different light doping levels (x = 0.03–0.09) were prepared by a solid-state thermal reaction and studied by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), energy dispersive analysis (EDAX), and optical diffuse reflectance spectroscopies. The prepared samples has been revealed that the increments in Zn-doping levels accompanied by vacuum heat treatment lead to the appearance of an additional V12O26 phase beside the pure V2O5 oxide, resulting not only in more donor vanadium atom liberation but also in multi-heterojunction component formation. Besides, Eg values decrease from 2.38 to 2.2 eV as Zn doping increases from x = 0 to x = 0.09. All previous observations improve the process of purifying water from pollutants by increasing the number of free carriers of V2O5 powder by adding Zn atoms and making vacuum heat treatments. The photocatalytic examination has been carried out using constants of 0.5 g and 0.01 g/L (10 ppm) of the catalyst quantity and MB-dye concentration, respectively, under Vis – irradiations. The acidic solution medium with a pH of 2 strongly motivated the degradation activity. The highest catalytic efficiency of 99.78% was attained by the (V2O5)0.91 Zn 0.09 compound within a time of 70 min and continued invariably for 5 hours in the dark. These catalytic results have proved the possibility of their reusability.

Exploring elucidation of red dye mixtures on woolen historical textiles via non-destructive spectroscopic analysis and multivariate cluster analysis

One of the foremost challenges facing analysis of historical textiles is that the gold standard technique—high performance liquid chromatography (HPLC)—is inherently destructive. This is especially problematic considering many historical textiles are exceptionally fragile, be it from age, poor care over time, etc. One proposed solution to this is the implementation of non-destructive, namely spectroscopic, techniques, such as diffuse reflectance (Fiber Optic Reflectance Spectroscopy, FORS). In this work, 204 well-provenanced red Norwich textiles were measured with FORS and analyzed to attempt to determine chromophore combinations used to dye the original textiles. To these ends, cluster analysis algorithms and spectroscopic domain knowledge were coupled with selective HPLC validation to assess overall ability of FORS to discern changes in chromophore combinations. It was found that the near infrared (NIR) region of the spectrum contained little meaningful information in multivariate space, while the VIS region, particularly 380–469 nm, showed a narrow visible region that was primarily responsible for clustering behavior that correlates with HPLC-validated samples. This indicates that FORS shows promise for discerning chromophores in textile swatches. Additionally, X-ray fluorescence (XRF) analysis was used to confirm that the observed FORS spectral inflection point shift in the 600 nm region did not correlate with the presence or type of mordant used when dying these textiles. From this work, three main conclusions can be drawn: (1) FORS adequately identifies visual infon, which shows reasonable correlation to HPLC-validated dye recipes, warranting further investigation, and indicating utility for cois or use for those with visual impairments; (2) XRF analysis confirms that the ~ 600 nm inflection point shift and mordant are not correlated when measuring dyed textiles, unless mordant is present below analytical detection limits or not present at all; (3) many documented structural-to-spectral relationships established in the conservation literature are too weak in dyed textiles for statistical analysis and, by extension, expert spectral identification.

Effect of yttrium on crystalline structure, morphology, and optical properties of HfO2 nanoparticles synthesized by the Pechini method

Undoped and Y-doped HfO2 (Y:HfO2) nanoparticles (NPs) were synthesized by the Pechini method. X-ray diffraction (XRD) analysis revealed that increasing Y concentration in HfO2 promotes the phase transition from monoclinic to tetragonal, with a crystallite size decrease from 5.3 to 2.9 nm. Phase changes were also confirmed by Raman spectroscopy, where the intermediate γ1-forms were identified. Moreover, microscopy images revealed the presence of spherical NPs between 6.7 and 4.6 nm. The diffuse optical reflectance (DOR) spectroscopy showed that HfO2 NPs with higher Y concentrations caused attenuation of light reflection in the UV region and enhanced it in the visible light region.

Tracing the history of past treatments: A multi-analytical study of a 16th-century panel painting copy after Raphael

A multi-analytical investigation and ad hoc sampling method designed to support the conservation treatment of a 16th-century panel painting are described in this work.The painting, titled Madonna of the Tent and owned by the Musei Reali Torino (Turin, Italy), had been historically attributed to Raffaello Sanzio and subsequently identified as a copy after the Master – the original version of which is displayed at the Alte Pinakothek in Munich (Germany). The conservation treatment was recently carried out at Centro per la Conservazione ed il Restauro dei Beni Culturali “La Venaria Reale” (CCR), located in Venaria Reale (Turin, Italy). The work was particularly opaque and yellowed, suggesting the presence of different overlaying varnishes and, likely, overpainting.The scientific study of this work had two main aims: knowing the exact number and composition of the overlaying varnishes to select the best cleaning solution, and detecting the possible presence of overpainting, over the original stratigraphy.Coupling macro X-ray fluorescence scanning (MA-XRF), hypercolorimetric multispectral imaging (HMI), and UV–vis–NIR fiber optic reflectance spectroscopy (FORS) allowed for general mapping and characterization of color paints and pigments. Observing and analyzing some cross sections with an optical microscope under Vis and UV light and SEM/EDS was essential for understanding the stratigraphy. An ad hoc sampling method and further micro-invasive analyses were required for an accurate study of the chemical composition of the varnishes and their position in the stratigraphy. Especially the image of a cross section under UV light was a guide to selectively remove the scrapings for Fourier transform infrared spectroscopy (FTIR) and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) analyses; based on perceptible differences in UV-induced luminescence (UVL) of the layers, sampling of the varnishes was carried out, layer by layer, under a UV lamp.This work describes the complex process necessary to answer crucial questions in the conservation field. The adopted protocol exploited the full ability and complementarity of each imaging and spot technique used. The outcomes and methodological approach enabled us to trace the history of the past treatments and support the recent conservation treatment of the painting.

Assessment of thermal maturity in Lower Cambrian organic-rich shale in south China using integrated optical reflectance and Raman spectroscopy of pyrobitumen

It is challenging to accurately determine the thermal maturity of Lower Cambrian overmature shale, which is widely distributed in South China. In this study, we report an integrated method of measuring optical reflectance and Raman spectroscopy of pyrobitumen to determine the thermal maturity of Lower Cambrian organic-rich shales that contained a highly aromatized organic matter chemical structure. The optical reflectance measurement was conducted on large-particle-size angular pyrobitumen to eliminate the interference of clay mineral matrix, and the Raman spectrum analysis is a statistical response of a highly thermally evolved pyrobitumen chemical structure. Raman analysis compensates for the limitation of optical anisotropy interference in optical reflectance measurements. There is a good agreement between optically measured pyrobitumen reflectance (PBRo) and pyrobitumen reflectance calculated by Raman parameters (RmcPBRo), reflecting only minimal effects of optical anisotropy on the average optical reflectance (PBRo) values of pyrobitumen with fine or irregular mosaic texture, further indicating reliability of this integrated method for analyzing overmature shale. Thermal maturity varies significantly in the Lower Cambrian organic-rich shales, ranging from 2.60 to 2.92% EqVRo in the western Hubei province (WHBP), 2.98–3.49% EqVRo in the southern Shaanxi province (SSXP), 3.20–3.38% EqVRo in the southern Sichuan province (SSCP) and 4.06–4.31% EqVRo in the southeastern Chongqing (SECQ). The degree of aromatization and the structural order of organic matter (OM) are abruptly intensified when thermal maturity reaches about 3.5–3.7% EqVRo, as indicated by the deconvolution of the D and G bands in the Raman spectrum of pyrobitumen. The abrupt change in chemical structure of OM provides evidence for further dividing the early and late stages of overmaturation at a boundary of 3.5–3.7% EqVRo. The Lower Cambrian organic-rich shales distributed in the Cambrian shale gas breakthrough areas are normally at the early stage of overmaturation (2.0% < EqVRo < 3.5–3.7%). Development of paleo-uplifts in the Cambrian shale gas breakthrough areas led to relatively shallow burial depth of Lower Cambrian shale distributed on the peripheral areas of paleo-uplifts and created favorable shale gas preservation condition with only rare and small-scale faults.

A study on the impact of [BO33−], [PO43−] and [SO42−] ions in normal cubic structures via structural and photoluminescence properties of Y2O3:Eu3+ phosphors

A series of Y2O3-AG: Eu3+ (where AG = Anionic Groups [PO43−, SO42− and BO33−]) nanophosphors were synthesized via a chemical combustion method and their structural and photoluminescence properties were investigated. The crystal structure and the surface morphology studies were analysed through the X-Ray powder diffraction (XRPD), Field-emission scanning electron microscopy (FE-SEM), Fourier-transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The XRD results showed that undoped Y2O3 phosphors crystalized in a cubic crystal structure, while the Y2O3-AG phosphors transformed from the pure Y2O3 cubic structures, except for SO42− based phosphor materials. The SEM micrographs showed that the particles were formed in the micrometer range with different sizes and shapes. The FTIR spectra revealed the presence of various structural groups in the Y2O3, Y2O3-AG: Eu3+ phosphors. Moreover, the optical diffuse reflectance spectroscopy (DRS) and photoluminescence (PL) properties were investigated. Using the DRS data, the optical band gap energy values were obtained from the Kubelka-Munk function theory. Upon 395 nm excitation, the Y2O3-AG: Eu3+ phosphors emitted red light at 615 nm wavelength. Among all the samples, the Y2O3-BO3: Eu3+ produced the highest intensity of red-light emission. The International Commission on Illumination color coordinates indicated that these phosphors are potential candidates for producing enhanced red color components in white light-emitting diode (W-LEDs) applications.

Insights into the dielectric function of plant leaves under water stress.

In this work, we present a practical approach combining experimental and theoretical analyses to assess water evaporation in Arabica coffee leaves. We examine continuously the changing water content of leaves through optical reflectance spectroscopy and mass loss measurements, beginning from a fully saturated stage and extending beyond the turgor loss point. We establish a relationship between the current water content and the dielectric function, based on the changing of the molecular water dipoles inside the leaf due to evaporation.

Deterioration effects of X-ray irradiation in artificially aged parchment

The effects of X-ray irradiation, a potential disinfection method, produced in parchment samples with different extent of artificial ageing have been investigated to analyse the possible superposition effects of the irradiation-induced damage with the existing ageing associated deterioration. The study was carried out in modern parchment samples in which different degrees of artificial ageing were induced by exposing them to severe hygro-thermal conditions for various durations. The aged samples were subsequently irradiated with increasing X-ray doses (350–4000 Gy). The consequent deterioration effects were analysed using light transmission analysis (LTA), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and fibre optic reflectance spectroscopy (FORS) in order to evaluate possible changes in, respectively, the hydro-thermal stability, the collagen protein structure (hydrolysis/denaturation) and the optical absorption/reflectance properties of the collagen protein. The results show increasing additional deterioration with irradiation dose for non-aged and moderately aged parchment, until damage saturation occurs for more intensively aged samples where no substantial additional deterioration is induced by the irradiation. The combined results indicate that the ageing produces the more substantial deterioration with respect to that induced by the irradiation treatment employed for disinfection purpose.

Bottom up anatase monodisperse nanoparticles grown on sepiolite showing high thermal stability and optimal optical properties for self-cleaning applications

Powder samples of anatase monodisperse nanoparticles (np's) have been in-situ synthesized from sepiolite microparticles doped with TiIV. The role of this clay is double, by one hand, it acts as a chemical reactor, and on the other hand, it becomes a solid substrate for particles, which pin them up avoiding Ostwald ripening process on heating. In this work we show the high thermal stability of these metastable anatase particles up to 850 °C, around 200 °C above the anatase/rutile transformation for ordinary powder particles. Relevant information about the electron bandstructure has been obtained both, by optical diffuse reflectance and emission spectroscopy, which revealed the nature of photon absorption and recombination around the band-gap which determine the utility of this materials as a self-cleaning agent for solid materials.

António Carneiro’s Painting Collection from the Municipality of Oporto. Study and Conservation in the 150th Anniversary of the Painter’s Birth

This paper presents a summary of the results obtained in the first approach ever made to the characterization of the materials and techniques used in the oil painting production by António Carneiro (1872–1930), one of the best portuguese painters in the transition from the 19th to the 20th centuries. A selection of ten oils on canvas belonging to the Municipality of Oporto were analysed using a set of non-invasive techniques: Infrared Reflectography, Ultraviolet Fluorescence Photography, X-ray Fluorescence Spectrometry, Fiber Optics Reflectance Spectroscopy and Fourier Transform Infrared Spectroscopy. The results obtained suggest the use of materials and techniques established in Europe at the turn of the century. The palette is composed of Pb, Zn, Hg, Cr, Cd, Cu, and Co-based pigments, associated with both traditional and recently introduced materials. The great missing element is Ti, associated with Titanium White, available on the market since 1918.

Laser cleaning of artificially soiled cotton fabric: Assessment of surface chemical effects

The effectiveness of the cleaning methods to remove soiling and stains from fabric artefacts is often limited by their complex microscopic and macroscopic structures, including fibre bundles, warp, weft, narrow folds, sewing deformations, and others. These structures may sometimes make the complete fabric cleaning very challenging, and they can easily be damaged. To approach such a problem, the potential of pulsed laser treatments of artificially soiled cotton fabrics has been investigated. Laser tests were carried out on the following samples: (i) untreated cotton fabric, (ii) unaged-sized cotton fabric, and (iii) aged-sized cotton fabric with soiling. Moreover, vacuum cleaning was also considered prior to laser irradiations to evaluate whether standard treatments can favour a more effective laser cleaning treatment. The fundamental wavelength and second harmonics of a Q-Switched Nd:YAG laser (1,064,532 nm) were used for the experimentation. The morphology and chemical composition of the laser irradiated mock-ups were characterised through a multi-analytical approach, including Fibre Optic Reflectance Spectroscopy (FORS), colourimetry, optical microscopy, Diffuse reflectance-FTIR (DR-FTIR) spectroscopy, μ-Raman spectroscopy and X-ray fluorescence spectroscopy (XRF). Contrarily to what was reported in some literature, these analyses allowed to demonstrate the absence of any chemical change of the cellulose fibres and the possibility to optimise the laser parameters in order to achieve satisfactory and non-invasive laser cleaning results.

Tiles from Aosta: A Peculiar Glaze Roof Covering

The 18th century roof tiles from the “Casa delle vigne”, located in the Aosta region (north-east Italy), were investigated as an example of a peculiar historical roof covering: ceramic tiles with a lead-based glaze finishing to waterproof them are used to create colourful patterns. A conservation project proposed the integration of the original tiles with new ones, produced according to traditional methods. Ancient and new tiles were analysed with Fiber Optics Reflectance Spectroscopy, micro-Raman, Fourier Transform Infrared Spectroscopy and X-ray Fluorescence Spectrometry, Thermogravimetry and Differential Scanning Calorimetry for understanding the composition and the production technology of this manufacture. Their resistance to freezing and thawing cycles was then tested, considering their exposure in the severe alpine climate of Aosta. The use of pure clays with low calcium contents, high firing temperature and lead-rich glazes was found in ancient tiles, able to outstand several freezing-thawing cycles without damages. Iron and copper pigments were used in old yellow and green glazes. Zinc-based pigment, low lead and calcium-rich glazes are used in the new ones, which remained mainly coherent to the ceramic body during the freeze-thaw test.

Changes in the production materials of Burmese textiles in the nineteenth century—dyes, mordants and fibres of Karen garments from the British Museum’s collection

The materials of six Karen textiles from the British Museum’s collection were investigated with the main aim of studying the production changes over the course of the nineteenth century and how these changes related to local and colonial trade networks. The textiles span chronologically from the 1830s to the early 1900s according to their attribution dates, and include traditional garments such as tunics and skirts, in addition to representing a broad colour palette and different dyeing and weaving techniques. The investigation was conducted non-invasively by using digital microscopy, broadband multispectral imaging (MSI) and fibre optic reflectance spectroscopy (FORS). The results guided a sampling campaign during which samples were taken and investigated by optical microscopy (OM), scanning electron microscopy energy dispersive X-ray spectrometry (SEM–EDX) and high-performance liquid chromatography coupled to diode array detector and tandem mass spectrometry (HPLC–DAD-MS/MS). Local natural dyes, such as red and yellow from Morinda citrifolia, lac dye (Kerria lacca), gamboge (Garcinia sp.), turmeric (Curcuma longa), indigo and tannins were found in the older textiles, supporting a possible early production, whereas mixtures of natural and synthetic dyes, including synthetic alizarin (CI 58000), rhodamine B (CI 45170), orange I (CI 14600), diamond green B (CI 42000), diamond green G (CI 42040), auramine O (CI 41000), naphthol yellow S (CI 10316), chrysamine G (CI 22250), crystal violet (CI 42555) and Pigment Red 53:1 (CI 15585:1) were identified in the later textiles. Observations on mordants revealed the use of aluminium, tin and chrome, whereas fibre characterisation highlighted the use not only of cotton (Gossypium sp.) but also of felted wool imported from Europe and Chinese silk dyed with the Chinese cork tree (Phellodendron chinense) yellow dye. The results draw an interesting picture of the introduction of new dyeing materials and techniques in Myanmar over the nineteenth century, and how these impacted the production of traditional Karen textiles.

The Non-Invasive Characterization of Iron Age Glass Finds from the “Gaetano Chierici” Collection in Reggio Emilia (Italy)

This work reports the results of the analyses performed on a set of glass finds from the “Gaetano Chierici” collection in the Civic Museums of Reggio Emilia. Forty-eight typologically heterogeneous glass finds were included in the list of the analyzed objects, dating from the fifth century BCE to the first century CE. The objects primarily consisted of glass beads; however, bangles, pinheads, and one vessel fragment were also included in the set. The items were analyzed using non-invasive spectroscopic methods that were implemented with portable equipment on the museum’s premises. Fiber optic reflectance spectroscopy was used to identify the coloring species in the glass matrix, while X-ray fluorescence spectrometry provided compositional information. Both techniques allowed for a discussion of the mechanisms of coloring and opacification, as well as the raw materials used for this purpose. The results provided a complex picture of the various colorants used to manipulate the appearance of the glass, which was a crucial aspect in the creation of the personal adornments represented by these glass items. The data revealed evidence of different sources of raw glass and colorants. Most of the samples were colored with cobalt, but iron and copper also influenced the color of many of them. Both white and yellow were utilized for the glass decorations, and these colors were achieved with the addition of either antimony-containing crystals or tin-containing ones. This finding suggests that the transition from antimonate to stannate started as early as the second century BCE. The “Gaetano Chierici” collection contains representative objects distributed throughout the investigated period. The results obtained here are a starting point for future studies of glass technology and provenance in the area.

Enhancing the MoS2/MoO3/ZnS/Zn-Heterojunction catalyst's photocatalytic performance for water organic pollutants

Pure and lightly Zn-doped (MoS2)0.97Zn0.03 powdered samples have been prepared by a simple economic method, structurally analysed by XRD, FT-IR, XPS, SEM& EDX, and optically characterised using optical diffuse reflectance spectroscopy. XRD analysis of the heat-treated Zn: MoS2 product revealed the formation of different multi-heterojunction semiconducting MoS2, MoO3 and barely visible ZnS components beside the metal-Zn element which were confirmed by FT-IR, XPS& EDX. The crystallite size for MoS2 samples decreased from 400.465 to 326.179 nm of (MoS2)0.97Zn0.03 , while the MoO3 and Zn constituents exhibit lower values of 108.884 & 8.045 nm, respectively. Their porosity percentages of ∼60%–67% are relatively high and beneficial for the photocatalytic process. The optical study showed a indirect allowed band gap with energy values of 1.2 and 0.9 eV for undoped and Zn doped, respectively. The photocatalytic study has been performed at different MB concentrations (10–20 ppm), and catalyst amounts (0.04–0.1 g) under dark, UV, and Vis irradiations assisted by pH and/or ultrasonic piezoelectric potential. The current enhanced result of 99.3% efficiency and a high performance figure of merit of ∼1045 min−1 were achieved in 20 s for (MoS2)0.97Zn0.03 with the capability of reusability.

Applying Gel-Supported Liquid Extraction to Tutankhamun's Textiles for the Identification of Ancient Colorants: A Case Study.

The identification of the dyes present on a linen fragment from the tomb of Pharaoh Tutankhamun is the objective of the present study. Fiber optic reflectance spectroscopy (FORS) was applied to the archaeological sample for preliminary identification of the dyes and to better choose the extraction methodology for different areas of the sample. The innovative gel-supported micro-extraction with agar gel and the Nanorestore Gel® High Water Retention (HWR) gel were applied to the archaeological sample after testing of the best concentration for the extraction of the agar gels substrates, performed on laboratory mock-ups by means of UV-Vis transmittance spectroscopy. Immediately after extraction, Ag colloidal pastes were applied on the gel surface and Surface Enhanced Raman Scattering (SERS) analysis was performed directly on them. The combination of information deriving from FORS and SERS spectra resulted in the successful identification of both indigo and madder and, in hypothesis, of their degradation products.