罗马壁画颜料分析的非侵入式制图方法外文文献

Please cite this article in press as A Dal Fovo et al Non invasive mapping methods for pigments analysis of Roman mural paintings Journal of Cultural Heritage 2020 https doi org 10 1016 j culher 2019 12 002 ARTICLE IN PRESS G Model CULHER 3698 No of Pages 8 Journal of Cultural Heritage xxx 2020 xxx xxx Available online at ScienceDirect Chemistry for Cultural Heritage at CNR Non invasive mapping methods for pigments analysis of Roman mural paintings Alice Dal Fovoa Anna Mazzinghib c Sergio Omarinia Enrico Pampalonia Chiara Rubertob c Jana Striovaa Raffaella Fontanaa aCNR INO Istituto Nazionale di Ottica Largo E Fermi 6 50125 Florence IT Italy bINFN Istituto Nazionale di Fisica Nucleare Via B Rossi 1 50019 Sesto Fiorentino IT Italy cUniversit degli Studi di Firenze Department of Physics and Astronomy Via G Sansone 1 50019 Sesto Fiorentino IT Italy a r t i c l e i n f o Article history Received 15 July 2019 Accepted 5 December 2019 Available online xxx Keywords Archaeological paintings A secco paintings MA XRF Multispectral scanning refl ectography Spectral correlation mapping a b s t r a c t The analysis of archaeological mural paintings may provide relevant information on the artistic tech niques and the pictorial materials used in the past expanding the knowledge of customs and technologies of ancient societies Given their location fragility and value it is generally required to analyze mural paintings in situ avoiding contact measurements sampling or pre treatments In this work a number of polychrome fragments from two recently discovered Roman villas have been studied with three non invasive techniques making use of transportable devices Macro X ray Fluores cence MA XRF elemental mapping multispectral scanning refl ectography and Fibre Optics Refl ectance Spectroscopy FORS Specifi cally the MA XRF elemental maps were compared with the spectral cor relation maps SCM computed from the Vis NIR images acquired with the multispectral scanner with the aim of displaying the distributions of the different pictorial materials while assessing the chemical composition of the pigments present The combined application of the two former mapping imaging tech niques represents a valid tool for the chemical and spectral characterization of archaeological paintings providing easy to interpret data for the professionals involved in the conservation of Cultural Heritage 2019 Elsevier Masson SAS All rights reserved 1 Introduction During the Roman Republican period 509 BC 27 BC wall paintings were often conceived as parietal decorations on plas ter with the primary purpose of differentiating the spaces inside the dwellings of the wealthy roman classes Besides this practical function the depicted fi gures encompassed an important commu nicative intent making use of a common and recognized language based on well known fi gurative schemes Having the two fold role of giving evidence both of the organization of the living space and of the technical competencies plaster wall paintings represent valu able means for enlarging and deepening the knowledge on the ancient societies In recent years two ancient rustic villas were discovered near Naples one in Quarto Flegreo and the other in Pozzuoli These fi ndings add up to the long list of Roman urban and rustic villas of priceless historical and cultural value fl ourished between the 5th and the 1st century BC mainly in Etruria Latinum and Cam pania Both villas were divided in two main sectors according to Corresponding author the ancient custom and testifi ed by the masonry techniques and the pottery found the pars urbana place of the social and business relations and the pars frumentaria where servants and workers took care of the production and processing of the products The Roman settlement of Quarto took its name from its distance on the fourth mile from Pozzuoli on the road axis connecting the port of Puteolis with the town of Capu Before being abandoned between the 70 75 and 120 AD the Quarto Flegreo villa was affected by a destructive event as attested by the excavations which revealed a layer of burnt material covering the collapsed elevated structure Many painted fragments were found inside this amount of material some of them analyzed in this study As regards the Pozzuoli villa during the Julio Claudian age from 27 BC to 68 AD a signifi cant renovation leaded to the expansion of the pars frumentaria to the detriment of the pars urbana and in that occasion two spaces on the lower terrace were walled up Recently such hidden places were opened and several typical Julio Claudian ceramics and fragment of mural paintings were found The Pozzuoli villa as shown by the abundant pottery discovered in the upper terrace was abandoned during the fi rst decades of the 5th century AD In this study fragments of painted plaster from the two villas have been analyzed and compared with the aim of investigating a https doi org 10 1016 j culher 2019 12 002 1296 2074 2019 Elsevier Masson SAS All rights reserved Please cite this article in press as A Dal Fovo et al Non invasive mapping methods for pigments analysis of Roman mural paintings Journal of Cultural Heritage 2020 https doi org 10 1016 j culher 2019 12 002 ARTICLE IN PRESS G Model CULHER 3698 No of Pages 8 2 A Dal Fovo et al Journal of Cultural Heritage xxx 2020 xxx xxx Fig 1 Some of the 20 analyzed fragments the Q and P labelled ones were found in Quarto Flegreo villa and Pozzuoli respectively common thread in techniques and materials used by the ancient artists within the same geographical area Frequently the detec tion in confi ned areas of the same chemical elements on painted objects suggests with some certainty the use of specifi c pigments In other cases however a more extensive study is required in order to reach an unambiguous identifi cation Through a synergic analyt ical approach involving complementary techniques it is possible either to validate or disprove some assumptions about the use of specifi c pigments The excavated fragments were numerically and typologically classifi ed basing on the number of colours the backgrounds and the decoration motifs After this qualitative evaluation twenty frag ments were selected to be analyzed Most of the fragments showed a uniform pattern or small ornamental details apart from one found at the Pozzuoli villa representing the profi le of a male fi gure Fig 1 Firstly a multi modal diagnostic approach was applied to ana lyze this latter fragment thanks to the presence of several pigments and to the quality of the manufacturing Three non invasive tech niques were applied conjunctly namely X Ray Fluorescence XRF imaging 1 2 Vis NIR multispectral scanning 3 7 and Fibre Optics Refl ectance Spectroscopy FORS 8 12 Specifi cally both MA XRF and VIS NIR multispectral scanning provide image data which are easily interpretable and accessible to many experts in the fi eld of conservation thus facilitating the collaboration between the different professionals FORS provides punctual and highly resolved spectral data which turn useful to analyze small areas in order to characterize and identify the pigments used Here ref erence spectra from the database of the National Institute of Optics CNR INO in collaboration with the Opifi cio delle Pietre Dure OPD were used for pigment identifi cation The Vis NIR images were then processed with the spectral correlation mapper SCM Spectral correlation was accomplished through a criterion of sim ilarity between the spectral image and a reference spectrum 13 which was extracted from the same Vis NIR images acquired with the multispectral scanner allowing for the discrimination between pigments based on their refl ectance trends In the last years there has been an ongoing interest to develop and apply this method as an analytical tool to map and identify artist s materials in situ 14 15 SC maps were compared with the MA XRF maps to verify the distribution of the pigments in the analyzed area Finally SCM was applied on all the fragments for a comprehensive view of the ancient artistic practice of mural paintings in the geographical area Quarto Flegreo and Pozzuoli 2 Research aim This study was aimed at showing the effectiveness of the combined application of non invasive optical techniques for in situ pigments analysis on ancient mural paintings Two mapping imaging methods i e X ray Fluorescence XRF and mul tispectral scanning refl ectography complemented by Fibre Optics Refl ectance Spectroscopy FORS were performed on a number of polychrome fragments from two recently discovered Roman villas In specifi c the MA XRF maps were compared with the spectral cor relation maps SCM computed from the Vis NIR images acquired with a multispectral scanner in order to display the distributions of the different pictorial materials while assessing the chemical composition of the pigments present The presented methodol ogy makes use of on fi eld based instruments and may provide chemical and spectral data in form of maps images which turn easy to interpret by the professionals involved in the conserva tion of Cultural Heritage The integration of analytical elemental information with multi spectral data processing provides the basis for a subsequent timesaving mapping enabling to highlight pig ments distribution on large surfaces up to 1 square metre in our case The so obtained spectral information properly related to elemental compositional information can be used for pigment identifi cation and mapping 3 Instruments and methods 3 1 MA XRF system for elemental mapping The device used in this study is a second generation XRF scanning system developed by the INFN network of laborato ries for Cultural Heritage studies CHNet As an improvement on traditional single spot measurements the scanner acquires ele mental maps which signifi cantly facilitate the interpretation of an artwork s complex composition proving effective in evidencing previous restorations and pentimenti 16 18 The scanning system is remotely controlled via homemade soft ware moving the measuring head by raster scanning in either horizontal or vertical direction Data output is a set of elemental maps where colour is attributed to every pixel as a function of the number of events detected in the energy range of the selected element The spectrometer allows the detection of elements down to Z 14 silicon in air making the use of an Amptek XR100 SDD with an energy resolution of 140 eV at Mn K line 19 For all the measurements presented herein the standard condi tions were the following 30 kV anode voltage Cr anode 100 A fi lament current 800 m collimator 500 m s scanning velocity and 250 m pixel size The maps here shown were elaborated by means of the PyMCA software by ROI procedure 3 2 VIS NIR multispectral scanner The VIS NIR Multispectral Scanner represents a breakthrough in refl ectographic analysis allowing for the simultaneous acquisition of high resolution aberration free images at different wavelengths in a huge spectral region The radiation refl ected by the painting Please cite this article in press as A Dal Fovo et al Non invasive mapping methods for pigments analysis of Roman mural paintings Journal of Cultural Heritage 2020 https doi org 10 1016 j culher 2019 12 002 ARTICLE IN PRESS G Model CULHER 3698 No of Pages 8 A Dal Fovo et al Journal of Cultural Heritage xxx 2020 xxx xxx 3 is detected in 32 bands 16 in the 400 800 nm VIS range with 20 30 nm spectral resolution and 16 in the 800 2400 nm NIR range with 60 120 nm spectral resolution by using a set of photodiodes coupled to proper interferential fi lters The painting s surface is scanned point by point with a spatial sampling of 4 points per mm 250 m with an acquisition time of 3 h per square metre The whole system is computer controlled via a dedicated software 3 3 Fibre Optics Refl ectance Spectroscopy FORS The instrument used is a commercial device Zeiss working in a 45 0 lighting detection confi guration operating in the spectral range 304 1700 nm with a spectral resolution of 3 and 6 m in the VIS and NIR range respectively and a spot diameter of about 3 mm Proper adjustment procedure was followed using reference standards Spectralon 3 4 Spectral correlation mapper SCM The spectral correlation mapper is a method of classifi cation for refl ectance spectra based on the comparison of spectral images with a reference spectrum accomplished through a similarity cri terion 20 21 SCM is based on the spectral correlation function SCF algorithm which can subtle differences between data cubes that may not be evident in other kinds of comparisons 22 It rep resents an improvement of SAM Spectral Angle Mapper which calculates the angles formed between the reference spectrum and the image spectrum treated as vectors in a space with dimension ality equal to the number of bands 20 since it takes into account the derivative of the Pearsonian Correlation Coeffi cient that elim inates negative correlation maintaining the SAM characteristic of minimizing the shading effect Spectra were selected in the region of interest area showing the same hue by means of a purposely developed software The tool enables to choose the diameter of the selected point in our case 250 m which is also the minimum size corresponding to the pixel size and the average was computed over three acquisition points selected within the same hue 3 5 Case study painted fragments Twenty fragments were analyzed and compared eleven of them are reported in Fig 1 Sixteen fragments were found in the Quarto Flegreo villa labelled Q1 16 some presenting a uniform colour pattern and others characterized by small ornamental motifs Four fragments P1 4 come from the Pozzuoli villa three of them P2 4 painted with a single pattern whereas one P1 showing a male pro fi le a half length fi gure which likely represents thiasos bacchico as suggested by the traces of a crown of ivy leaves sacred to the god of wine The face is depicted in profi le with quite realistic connota tions as the full lips and an aquiline nose are outlined by hard paint stroke and the physiognomic features are obtained through the wise use of subtle brushstrokes A brown line defi nes the eyelids the nose and the mouth whereas light touches of white and yellow impart three dimensionality to the face The man s right shoulder is wrapped in a purple cloak and the entire fi gure is placed into a red rhombus delimited by two white and brown lines probably inscribed within a square with yellow and green corners The frag ment was probably part of a series of decorative elements meant to divide the central and the lateral spaces inside the house The fi gurative elements recall the parietal decorations of the IV style phase in which it is common to fi nd medallions or squares depict ing busts of characters in pairs or isolated often the Dionysian thiasos in the centre of the panels inside the median area of the wall However the small size of the geometric elements as well as the miniaturistic framework of the depicted details suggest dating Fig 2 XRF sum spectrum of the examined area The enlargement of the range 1 5 3 keV dotted red rectangle up right shows the presence of the peak attributed to Hg and S Ni is due to the primary X ray beam and not to the sample the execution before the 40 45 A D i e in the fi nal phase of the III style 4 Results and discussion The three formerly described analytical techniques were applied jointly to obtain the elemental characterization MA XRF and the areal Scanning Multispectral VIS NIR Refl ectography and punc tual FORS spectral refl ectance factor of the analyzed surface Spectral correlation maps SCM were then extracted from the spectral images with a dedicated software in order to visualize the distribution of the pigments on the painted area based on the anal ysis of the spectral behaviour of the analyzed points Data acquired on fragment P1 are presented and discussed fi rstly focusing on the different areas of interest background face and eye leaves Then the spectral correlation analyses on the other fragments are reported based on the results obtained on P1 4 1 Fragment P1 MA XRF analyses enabled the recognition of several elemental components whose main peaks are shown in the XRF spectrum Fig 2 The distribution of each element on the painted surface can be observed in the respective elemental map reported in Fig 3 4 1 1 Red background The same distribution of Hg and S in the elemental maps sug gests the use of cinnabar HgS for the red background Although Hg M lines and S K lines 2 19 keV and 2 31 keV respectively partially overlap the fi tting of the spectra allows the discrimina tion of both the elements contributions in the spectrum Fig 2 The differences in signal intensities in the Hg S map are likely due to X rays self absorption effects as Hg L lines 9 99 keV are more energetic than the Hg M lines 2 12 keV L lines are less absorbed by the overlying layers as those of the fl esh tone This also explains the inhomogeneous pattern of Hg L map in the fi gure s face proba bly due to the patchy distribution of the underlying red background and not to in homogeneities of the fl eshtone itself as in that case Hg M lines would have shown the same distribution of the L lines The use of cinnabar is confi rmed by the averaged refl ectance spectra acquired on the background with FORS and extracted from the Scanner Multi Vis NIR dataset Fig 4a which are shown in comparison with the reference spectrum of cinnabar Furthermore the spectral correlation map computed in the visible and near infrared range and expressed in black and white scale where white represents the maximal correlation and black the minimal Fig 4b clearly highlights the homogeneous distribution of cinnabar on the Please cite this article in press as A Dal Fovo et al Non invasive mapping methods for pigments analysis of Roman mural paintings Journal of Cultural Heritage 2020 https doi org 10 1016 j culher 2019 12 002 A