Fiber Optic Reflectance Spectroscopy Research Articles

Seventeenth-Century Barniz de Pasto Objects from the Collection of the Hispanic Society Museum & Library: Materiality and Technology

The Hispanic Society Museum & Library (HSML) holds a collection of nine viceregal barniz de Pasto objects, made by Indigenous artisans in the 17th and 18th centuries. Designed to imitate Asian lacquers and intended for European aesthetic tastes, barniz de Pasto is an example of Indigenous technique and knowledge that has survived to the present day. An in-depth analysis of five of these barniz de Pasto objects, dated to the first half and last quarter of the 17th century based on their iconography, was carried out through a combination of non-invasive and micro-invasive techniques, including portable X-ray fluorescence (pXRF) spectroscopy to investigate the possible presence of inorganic pigments, and fiber-optics reflectance spectroscopy (FORS) and reflectance imaging spectroscopy (RIS) to provide molecular information on colorants and their distributions across the objects. Dyes and pigments were also identified using Raman spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, and liquid chromatography/mass spectrometry (LC/MS). The nature of the resin was determined by FTIR and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), while the decoration stratigraphy and composition were analyzed by scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS). This paper confirms the use of mopa mopa, the resin used in the barniz de Pasto technique, in two objects not previously analyzed, and identifies indigo, insect-based red, calomel, lead white, and an unknown flavonol-based yellow dye, and challenges the use of calomel as a temporal marker for these works. Taken together, these results expand our understanding of the material use and explorations undertaken by artists during this time period to create such elaborate and enduring objects.

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.

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.

The Colors in Medieval Illuminations through the Magnificent Scriptorium of Alfonso X, the Learned

This pioneering work studied the medieval color palette of four manuscripts produced in the scriptorium of Alfonso X, king of the Crown of Castile (r. 1252-84), including the Songs of Holy Mary (Cantigas de Santa Maria, in Rich Codex and Musicians’ Codex), Lapidary (Lapidario), and Book of Games (Libro de los juegos). Scientific analysis based on fiber-optics reflectance spectroscopy in the visible and Raman spectroscopy showed a color palette based on lapis lazuli, indigo, azurite, vermilion, red lead, orpiment, yellow ochre, two different greens (bottle green and vergaut), lead white, carbon-based black, and most importantly, brazilwood pinks, reds, and purples. So, it is now the first reported use of this lake pigment in European medieval manuscript illumination. The painting technique is also discussed. The diversity of colors and techniques, with the presence of lapis lazuli, brazilwood lake pigments, purple, and gold, demonstrates Alfonso X’s desire to produce sumptuous manuscripts.

The Non-Invasive Spectroscopic Study of a Parchment Object from the National Central Library of Florence: The Hebrew Scroll

The Hebrew Scroll, catalogued as Magliabekian Manuscript III 43 and belonging to the National Central Library of Florence (BNCF), is a membranous richly decorated scroll, with colorful depictions of sacred sites through the Holy Land to Lebanon along with handwritten texts in Hebrew and notes in Italian. Despite the fact that the manuscript was originally catalogued as an “object of no artistic or scientific value”, recent paleographic studies dated it to the XIV century and highlighted it as the oldest scroll still available, depicting holy places from Egypt to Lebanon. Nevertheless, precise dating, authorship, and the interpretation of its original function are still uncertain. A suite of complementary techniques was used, including photographic documentation in visible (VIS) light in diffuse light, grazing light, and transillumination, luminescence induced by ultraviolet (UV) radiation, imaging spectroscopy (IS), Macro Area X-ray Fluorescence (MA-XRF), and spot analyses such as fiber-optic reflectance spectroscopy (FORS) in the UV, VIS, and near-infrared (NIR) regions, Fourier transform infrared spectroscopy (FT-IR) in external reflectance mode (ER), and micro-Raman spectroscopy. The results of the non-invasive diagnostic campaign enabled the identification of several constituting materials (parchment, pigments, binder, and inks). The identified materials were consistent with the proposed dating and geographical manufacturing area of the artefact.

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.

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.

Multi-analytical investigation into the materials and techniques of paintings on Northern Wei Dynasty (398–494 CE) coffin planks excavated from Shanxi, China

This study combined various non-invasive and micro-invasive analytical techniques to investigate the production process of coffin plank paintings excavated from a Northern Wei tomb in Zhijiabao Village, Datong City, Shanxi Province. Fiber-optic reflectance spectroscopy, portable Raman spectroscopy, and portable X-ray fluorescence spectroscopy were employed for in-situ non-invasive detection of coffin panel paintings. On that basis, micro-samples in smaller amounts than that of previous studies of the same type were collected and analyzed through optical microscopy, confocal micro-Raman spectroscopy, and scanning electron microscopy-energy dispersive spectroscopy. The results showed that the studied coffin plank decoration was painted after applying a layer of yellow primer to the plank surface. Specifically, cinnabar was used as the red material, pararealgar was used as the yellow color, an indigo and orpiment mixture was used as the green substance, the blue pigment was most likely an indigo and lead white mixture, gypsum was used the white material, and carbon black was used as the black pigment. Notably, the studied coffin plank was painted with a mixture of inorganic and organic materials to present the green and blue colors. This study provided not only a scientific basis for the conservation and restoration of this artifact but also new information for the research on Northern Wei art history.

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.

Characterization of Pigments and Materials of the Original Body and Additions of the Book of Hours 50,1,1 from the Brazilian National Library

The Brazilian National Library has in its collection a luxurious book of hours from the Royal Library of Portugal. For a long time, it was believed to have been made by the Italian painter Spinello Spinelli for King Fernando I (1345-1383) in 1378. This is due to the information in its colophon and the presence of a coat of arms of the Portuguese crown on the opening folio. According to recent studies, this is an example of a rare group of Flemish books of hours from ca. 1460 to English use – raising questions about the codex origin, dating, recipient, and route. To collaborate in this investigation, a material characterization study was proposed using non-invasive analyses, such as optical microscopy (OM), X-ray fluorescence (XRF), and fiber optics reflectance spectroscopy (FORS). The following pigments and materials were identified: lead white, minium, vermilion, lead-tin yellow, azurite, malachite, brazilwood lake, iron gall inks of different compositions and metals in foil or powder, namely gold and silver; moreover, the identification of lapis lazuli, Armenian bole and a different red organic lake in the colophon was decisive in corroborating the thesis of art historians, confirming the production period of the original body of the manuscript to the 15th century and that the colophon and coat of arms are later additions. Additionally, it was revealed that the coat of arms was superimposed on a previous shield.

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.

The Book of Uí Mhaine: An Interdisciplinary Analysis of the Materiality of the Gaelic Manuscript Tradition

This paper presents the findings of the first multi-analytical investigation of the Book of Uí Mhaine, one of the largest Gaelic Books surviving from the medieval vernacular period. A combination of protein analysis, point X-ray fluorescence spectroscopy (XRF), multispectral imaging (MSI), point Fiber-Optic Reflectance Spectroscopy (FORS) and point Raman spectroscopy was used to perform a systematic investigation of the Book of Uí Mhaine’s constituent materials, including parchment, inks and pigments. The analysis revealed that the parchment was made of calfskin, both blunt tools and Pb-containing materials were used for ruling the pages throughout the manuscript, and iron-based inks were used to write the content of the book. The decoration was restricted to the initial letters and rubrication across the body text. The decoration color palette was limited to yellow and red, comprising arsenic-, mercury- and lead-based pigments. A copper-based green pigment was found only on one folio. The scientific knowledge acquired through this multi-analytical approach complemented a substantial corpus of knowledge already built by Gaelic scholars, paleographers, codicologists and conservators. This work not only allowed for the consolidation of existing information on methods and materials used for the production of medieval Gaelic manuscripts but also laid the basis for future comparative work with other contemporary traditions in Ireland and Europe.

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.

First evidence and characterisation of rare chrome-based colourants used on 19th-century textiles from Myanmar

First evidence for the use of the chrome yellow dyeing method was obtained on late 19th-century Karen textiles from Myanmar. Non-invasive observations obtained by digital microscopy and fibre optic reflectance spectroscopy (FORS) provided hints of the possible presence of non-conventional organic colourants in yellow, orange and green threads used to produce three textiles under investigation. Micro-samples analysed by scanning electron microscopy coupled to energy dispersive X-ray spectroscopy (SEM-EDX) and micro-Raman spectroscopy enabled PbxCrOy formulations directly precipitated onto cotton fibres to be identified and characterised in these threads. Complementary analyses by high pressure liquid chromatography coupled to diode array detector and tandem mass spectrometry (HPLC-DAD-MS/MS) revealed that in the orange and green threads the chrome-based colourants were over-dyed with local natural dyes, thus revealing an unprecedented dyeing scenario, in which cotton threads imported from Europe were over-dyed locally by Karen people to obtain desired colour shades. Additionally, while yellow threads showed the presence of chrome yellow (lead chromate - PbCrO4), orange and green threads mostly contained chrome orange (basic lead chromate – Pb2CrO5 or PbCrO4·Pb(OH)2), which led us to hypothesise that chrome yellow partially transformed into chrome orange due to the over-dyeing process performed in alkaline conditions. This study raises awareness of the need for detailed spectroscopic characterisation coupled with high resolution mass spectrometric analysis to study complex mixtures of dyeing materials in historic textiles and has strong implications for advancing our understanding of the impact of British colonisation on traditional textile-making in Myanmar.

Reflectance Spectroscopy as a Novel Tool for Thickness Measurements of Paint Layers.

A major challenge in heritage science is the non-invasive cross-sectional analysis of paintings. When low-energy probes are used, the presence of opaque media can significantly hinder the penetration of incident radiation, as well as the collection of the backscattered signal. Currently, no technique is capable of uniquely and noninvasively measuring the micrometric thickness of heterogeneous materials, such as pictorial layers, for any painting material. The aim of this work was to explore the possibility of extracting stratigraphic information from reflectance spectra obtained by diffuse reflectance spectroscopy (DRS). We tested the proposed approach on single layers of ten pure acrylic paints. The chemical composition of each paint was first characterised by micro-Raman and laser-induced breakdown spectroscopies. The spectral behaviour was analysed by both Fibre Optics Reflectance Spectroscopy (FORS) and Vis-NIR multispectral reflectance imaging. We showed that there is a clear correlation between the spectral response of acrylic paint layers and their micrometric thickness, which was previously measured by Optical Coherence Tomography (OCT). Based on significant spectral features, exponential functions of reflectance vs. thickness were obtained for each paint, which can be used as calibration curves for thickness measurements. To the best of our knowledge, similar approaches for cross-sectional measurements of paint layers have never been tested.

New insights on Teotihuacan color technology: a proposal of a technological style for mural painting

Teotihuacan, the main city of the Classic period in Central Mexico (ca. 150/200–650 CE), was among many things, a colorful city. Through its application on mural painting, ceramics, lapidary, bone, textiles, and the human body itself, coloring materials gave meaning to the Teotihuacan reality. This research presents color as a socio-technological phenomenon from the archaeology of color, the anthropology of technology, and the application of the concept of technological style.From this scope, pictorial palettes of mural painting fragments from three Teotihuacan architectural compounds were studied by digital microscopy, colorimetry, fiber optic reflectance spectroscopy (FORS), X-ray fluorescence (XRF), Raman spectroscopy, infrared spectroscopy (FTIR), and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) in order to identify the color technology of pigments. This approach led us to identify materials shared by the three studied compounds, red and yellow earths, cinnabar, malachite, pseudomalachite, azurite, and the Teotihuacan grayish blue, found to contain a mix of bone black with calcite. Our results contribute to the discussion on the use of raw materials and their mixtures. We observed a standardization of pigment technology in Teotihuacan mural painting through the use of shared and standard formulations with four indicators that we propose as markers of a technological style for pigments, along with variations in the color materials that evidence the use of different strategies for the procurement and distribution of raw materials among the diverse architectural assemblages of the city.

Non-Invasive Characterisation of the Wall Paintings in the Byzantine Church of Palazzo Simi (Bari, Italy) and Digital Photogrammetric Survey for a Pigment Mapping

The paper illustrates the results of a non-invasive characterisation of pigments and their mixtures in the pictorial surfaces of the wall paintings (10th century) found in the Byzantine church of Palazzo Simi in Bari (Italy). The investigation techniques included portable digital polarised microscopy, fibre optic reflectance spectroscopy (FORS) and X-ray fluorescence spectroscopy (XRF). Data comparison supported the recognition of red and yellow ochres, green earth, vine black, minium and Egyptian blue. The presence of some pigment mixtures demonstrated the recurrence of specific technical expedient used by local medieval artists in order to simulate more expensive pigments, which enabled contribution to the understanding of the valuable artistic tradition of the Apulian Middle Age. Both for purposes of conservation and fruition of the site, which is not always accessible, and due to the complexity in taking suitable photographs for the representation of results, the latter was performed on orthophotos extracted from a digital photogrammetric 3D model of the whole archaeological site. By means of chromatic overlapped layers, an interactive compositional map of the pictorial surfaces was produced.