Gold,gildings, and tumbaga from the Moche tomb of the Lady of Cao: An EDXRF test for the internal ratio method

Gold, gilded copper, gilded silver, and tumbaga artifacts from the Moche tomb of the Lady of Cao, dated around 300 A.D., were analyzed by energy-dispersive X-ray fluorescence analysis. These artifacts are multilayered structures, which can be “reconstructed” using the K or L rays ratio of the chemical elements present in the layers. For example, in the case of gilded copper, the ratios Au (Lα/Lß), Cu (Kα/Kß), and Au-Lα/Cu-Kα, altered with respect to bulk gold or copper, can be used to determine the gilding thickness. An ideal test of this method was recently offered by the study of 15 big spears on gilded copper, a necklace composed of 12 small heads on tumbaga (a poor gold-alloy subject to depletion gilding), and a nose decoration on gilded silver. All these artifacts were found in (or close to) the tomb of the Lady of Cao, discovered 10 years ago in the north of Peru, close to Trujillo. The “internal ratio” method is described and discussed.     

Portable XRF study of pigments applied in Juan Hispalense’s 15th century panel painting

Several medieval paintings and polychrome sculptures have been analysed in the frame of a collaboration between the Fine Arts Museum of Seville and the National Centre of Accelerators, dedicated to a non‐destructive study of artworks that belong to the wide museum’s collection. Among the oldest artworks in the collection is the panel painting Archangel St. Michael attributed to Juan Hispalense, one of the first painters in the 15th‐century Seville known by name. The panel was analysed by a portable X‐ray fluorescence (XRF) to get more information about the pigments applied and to identify possible later interventions. The results showed that the pigments were those commonly used in that period. Lead white was found in the preparation of the painting and in colour layers. For yellow colour, yellow ochre was used, while for the red one, the painter usually mixed red earth and vermillion. Blue pigment is azurite, while the copper‐based green one could not be determined more specifically by XRF. Brown colour is made with yellow ochre and organic black or, in some cases, umbra. Black pigment is probably bone or ivory black. Many decorative parts of the panel are gilded, which were confirmed by Au peaks. Later interventions were carried out on the base of Ti–Zn white mixed with earth pigments, while for green areas such as Archangel's wings also chrome green was applied. The research is part of a larger study which is still going on, whose aim is to gain more knowledge about the 15th‐ and 16th‐century Spanish painting and polychromy. Copyright © 2011 John Wiley & Sons, Ltd.     

XRF study on the gilding technique of the fresco ‘Crocifissione con Santi’ by Beato Angelico in the San Marco monastery in Florence

This study focused on the gildings of a famous Italian fresco, the Crocifissione con Santi by Beato Angelico, exploiting the XRF spectrometer developed at the LABEC laboratory. This can be considered the first scientific study on the gilding technique on frescoes of Beato Angelico. In order to characterise the original gilding technique and identify restored parts, more than 30 points were analysed in different areas of the wall painting, mostly in halos and decorations. In particular, the main goal was to verify whether Beato Angelico used the composite tin–gold foil, the most common gilding technique during the Italian Renaissance. This study allowed discriminating the original from the restored gildings, and to characterise the layers in both cases, by means of iron Kα/Kβ ratio. Copyright © 2015 John Wiley & Sons, Ltd.     

Study of medieval enamelling on gilded objects combining SEM-EDAX and PIXE

A set of fragments of metallic artefacts from the medieval period excavated from Ciudad Real in Spain has been studied. The objects are gilded copper buckles with a champlevé enamelling decoration. The composition of predominantly blue-coloured enamels has been analysed using three non-destructive techniques, SEM-EDAX (scanning electron microscopy coupled with energy-dispersive X-ray analysis), X-ray fluorescence (XRF) and PIXE (particle-induced X-ray emission). Analyses show that Co is responsible for the blue colour. The results of the two techniques are compared, as well as the main components which constitute the enamel. Analyses suggest that Cu is responsible for red colour.     

Analysis of the spectacular gold and silver from the Moche tomb ‘Señora de Cao’

On the north coast of present‐day Peru, between the Andes and the Pacific Ocean, approximately between 100 and 600 ad , the Moche civilization prospered. The Moche were very sophisticated artisans and metal smiths, so that they are considered the finest producers of jewels and artifacts of the region. Their metalworking ability was impressively demonstrated by the excavations of the tomb of the ‘Lady of Cao’ (dated around third–fourth century ad ) discovered by Regulo Franco in 2005. Impressive is the beauty of the artifacts, and also the variety of metallurgical solutions, demonstrated by not only the presence of objects composed of gold and silver alloys but also of gilded copper, gilded silver, and tumbaga, a poor gold Cu‐Au alloy subject to depletion gilding. About 100 metal artifacts from the tomb of the Lady of Cao, never before analyzed, were studied by using various portable equipments based on following non‐destructive and non‐invasive methods:

• energy‐dispersive X‐ray fluorescence with completely portable equipments;
• transmission of monenergetic X‐rays;
• radiographic techniques; and
• optical microscopy.

Gold objects and gold areas of nose decorations are characterized by approximately the same composition, that is, Au = (79.5 ± 2.5) %, Ag = (16 ± 3) %, and Cu = (4.5 ± 1.5) %, while silver objects and silver areas of the same nose decorations show completely erratic results, and a systematic high gold concentration. Many gilded copper and tumbaga artifacts were identified and analyzed. Further, soldering gold–silver was specifically studied by radiographs. Additional measurements are needed, particularly because of the suspect that depletion gilding was systematically employed also in the case of some nose decorations. Copyright © 2016 John Wiley & Sons, Ltd.     

Thin thickness gilding determined by x-rays ratios from EDXRF-spectra

A by-product of energy-dispersive X-ray fluorescence (EDXRF)-analysis consists of using the ratios of selected X-ray peaks to determine the thickness of multilayered objects. Three different methods were developed in the past, all because the two main K or L X-lines from an EDXRF spectrum emitted by a chemical element have a distinct energy and are differently attenuated by an overlying layer. This specific subject has many papers dedicated, but only a few considerations were devoted to the limits of these methods, that is, the range, for example, of gold thickness that can be usefully determined by each method. This paper defines these limits in the specific case of thin gilding (with d < 1 μm). Three typical situations were considered, and the following artefacts were studied: two artefacts on gilded lead, where the gold leaf is superimposed to a white lead pigment, both in the painting “La Fornarina” of Raphael, dated 1520 AD, and in the imperial carriage of Dom Pedro II emperor of Brazil. In this last case, the white lead pigment was painted over the wood structure of the carriage; four artefacts on gilded copper, three crowns and a pendant, from the tomb of the Lady of Cao, from the Moche civilization of the North of Peru, dated around 350 AD; finally, an artefact on gilded silver, a vase from the Chavín civilization of the North of Peru, dated around 1000-200 BC.     

Atacamite as a natural pigment in a South American colonial polychrome sculpture from the late XVI century

The image of Our Lady of Copacabana is a gilded polychrome sculpture manufactured in maguey wood at the end of the 16th century. It is a highly devotional image in the Andean region and her sanctuary lays at the shores of the Titicaca Lake in Bolivia. In this study, a green sample taken from the Virgin's veil has been analyzed with the aim to identify the green pigment and the gilding technique. The green pigment layer covered completely the shiny color of the gilded area. First, the cross section of the sample was examined by optical microscopy revealing the presence of green crystals on a white layer; beneath it, a gold leaf on a red bole was observed. Scanning electron microscopy‐energy dispersive spectroscopy analysis allowed the identification and quantification of copper and chloride in the green pigment layer. Analysis by micro‐Raman spectroscopy indicated the presence of atacamite (Cu₃Cl₂(OH)₃) as the green pigment. Although this compound has been identified as a degradation product of copper pigments or of metallic objects containing copper, in this polychrome sculpture, atacamite was used as the green pigment and is identified for the first time as a mineral pigment in a colonial sculpture made in the Viceroyalty of Peru. Copyright © 2012 John Wiley & Sons, Ltd.     

Thickness determination of gold layer on pre‐Columbian objects and a gilding frame,combining pXRF and PLS regression

In conservation, restoration and characterization studies of art and archaeological objects, the improvement of analytical techniques is a tendency. X‐ray fluorescence (XRF) is a versatile technique, and it has been widely used in the last decades for characterization of a great variety of materials (metals, glass, paints, inks, ceramics, etc.) applied to cultural heritage studies. Besides the chemical composition, it is possible to infer the layer thickness through XRF, enabling a general knowledge of the manufacturing techniques implemented by the culture of origin, as well as the association with the technological level reached for the production of each kind of artefact. The aim of this study is to introduce an alternative way for gold thickness determination of coatings in cultural heritage objects, combining portable XRF data and partial least square regression. As a case of study, we present the use of this methodology in portable XRF measurements performed in situ on a gilding frame in Brazil and in two pre‐Columbian artefacts from Chavin culture in Peru. Gold layers with thicknesses determined by Rutherford backscattering spectrometry (RBS) were used as standards to perform a calibration model and to check the methodology before its application to unknown artefacts. Copyright © 2016 John Wiley & Sons, Ltd.     

The composition and technology of polychrome enamels on Chinese ruby-backed plates identified through nondestructive micro-X-ray fluorescence

This research presents non-destructive analyses of Chinese enamelled copper and porcelain decorated with polychrome enamels. This study utilises two key, high-value art works with complex enamelling in the collection of the Victoria and Albert Museum (London, UK) to elucidate the composition and technology of objects with ruby-backed decoration. These plates date from early Qing dynasty and are associated with the Yongzheng (1723–1735) and early Qianlong (1735–1796) periods. The goal of this research is to investigate the hypothesis that ruby-backed plates in these two mediums are decorated with the same enamels and possibly manufactured in mutual enamelling workshops, which is a current topic of debate among scholars. Ten different enamel colours and the gilding on each plate were analysed and evaluated with micro-X-ray fluorescence to study the opacifiers and pigments. The results show that the enamels on these two works utilise the same opacifier and the consistent pigments in the white, ruby, pink, green, yellow, turquoise green, and blue enamels. Compositional differences were identified in the underdrawings, purple enamels, and gilding. The results demonstrate that Chinese painted enamels and overglazes on porcelain share mutual technology in most, but not all, of the polychrome decoration, which impacts upon our knowledge of technological organisation in the manufacture of these objects. Micro-X-ray fluorescence has been shown to be an effective and robust technique for the nondestructive study of decorative surfaces in these two material types.     

Multilayered artifacts in the pre-Columbian metallurgy from the North of Peru

Three types of alloys were recognized when analyzing pre-Columbian artifacts from the North of Peru: gold, silver, and copper alloys; gilded copper and silver; silvered copper; tumbaga, i.e., copper or silver enriched on gold at the surface by depletion gilding. In this paper, a method is described to differentiate gold alloys from gilded copper and from copper–gold tumbaga, and silver alloys from silvered copper and copper–silver tumbaga. This method is based on the use of energy-dispersive X-ray fluorescence, i.e., on a sophisticated analysis of XRF-spectra carrying out an accurate determination of Cu(K _α /K _β ), Ag(K _α /K _β ), Au(L _α /L _β ), and Au-L _α /Cu-K _α or Ag-K _α /Cu-K _α ratios. That implies a dedicated software for the quantitative determination of the area of X-ray peaks. This method was first checked by a relevant number of standard samples and then it was applied to pre-Columbian alloys from the North of Peru.     

Colorando Auro: contribution to the understanding of a medieval recipe to colour gilded silver plates

The colour of gildings can be modified by many artistic techniques. This article refers to the possibility of a specific chemical treatment to change the colour of gildings. The model samples—gilded silver plate, the mixture and the application of a medieval recipe based on ancient writings from Theophilius and Cellini have been described. We propose a strategy to identify the chemical processes involved in the change of colour of the metallic surface through the advanced study of these model samples. Synchrotron X-ray photoelectron spectroscopy and X-ray absorption spectroscopy were carried out both on the gilding with and without the application of the treatment with the aim to understand the chemical reactions occurring during the treatment.     

Gilding and pigments of Renaissance marble of Abatellis Palace: non‐invasive investigation by XRF spectrometry

Most of the artworks constituting the collection of Renaissance statuary of Abatellis Palace in Palermo (Sicily) show evidence of colour layers and fragments of gold foil that probably once covered the whole marble surface. The restoration of some of these statues has allowed to carry out archaeometric studies about the painting technique and to highlight the original materials and inclusion present on the precious marbles by two famous Italian sculptors of the Renaissance, Francesco Laurana and Antonello Gagini. The measurements have been performed in situ through the integrated use of two non‐invasive techniques: visible fluorescence stimulated by ultraviolet light and X‐ray fluorescence. The ultraviolet‐induced fluorescence analysis has provided additional information on the conservation status of marble surfaces by differentiating the pictorial materials and highlighting the presence of gilding and pigment traces through their characteristic fluorescence response. The observation in ultraviolet light has been used as valuable guide for the identification of the significant points to be analysed by X‐ray fluorescence to characterise the original materials. X‐ray fluorescence measurements have cast light about their chemical composition and stratigraphical structure. Pictorial layers were identified: vermilion for red layers, blue pigment based on copper for blue layers and pure gold leaf for gilding layers. Principal component analysis of the data was capable of clustering the different painting materials, discriminating through their chemical content. The results represent an important scientific support both to the hypotheses about the original look of the artworks and to the resolution of restoration and conservation questions still open. Copyright © 2012 John Wiley & Sons, Ltd.     

Study of ancient Islamic gilded pieces combining PIXE-RBS on external microprobe with sem images

Numerous metallic objects with very aesthetic and technological qualities have been recovered by archaeological excavations. Adequate processes of restoration and conservation treatments require the accurate determination of the elemental composition and distribution within the objects, as well as the identification of the nature and distribution of the corrosion products. Ideally the identification method should cause no alteration in the sample. In this work, different archaeological pieces with a gilded look have been characterized using simultaneously PIXE and RBS at the CMAM external microprobe in order to study the gilding metalworking done in the Iberian Peninsula during the Middle Ages. The gold layer thickness and its elemental concentrations of Ag, Au and Hg were determined by both techniques and compared with the scanning electron microscopy images obtained for some fragments of pieces. PACS  29.30.Kv; 87.64.-t     

The formation of chlorine-induced alterations in daguerreotype image particles: a high resolution SEM-EDS study

The daguerreotype image, composed of nanosized silver–mercury or silver–mercury–gold amalgam particles formed on a polished silver substrate, is particularly sensitive to deterioration by chlorine-containing compounds resulting in the formation of AgCl that generates redeposited silver upon exposure to UV and visible lights. In the present study, alterations caused by chlorides on daguerreotype test samples prepared following 19th century recipes were studied. The dependence of variations in the production steps of daguerreotypes, such as multiple sensitization and gilding, on the impact of the exposure to chlorine were analyzed by scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDS) and atomic force microscopy (AFM), complemented by X-ray fluorescence (XRF) and Raman spectroscopy. It was observed that AgCl nucleates on the image particles and in the substrate defects, regardless of the particle density or the sensitization process. In gilded samples, Au was observed over the image particles and the polished silver substrate as a tightly packed grainy layer, which conformably follows the polishing irregularities. For the first time it is shown that Au preferentially accumulates on top of the image particles. This gold layer does not protect the image from chlorine-induced deterioration.     

Visualizing the 17th century underpainting in Portrait of an Old Man by Rembrandt van Rijn using synchrotron-based scanning macro-XRF

In 17th century Old Master Paintings, the underpainting generally refers to the first sketch of a composition. The underpainting is applied to a prepared ground using a monochrome, brown oil paint to roughly indicate light, shade and contours. So far, methods to visualize the underpainting—other than in localized cross-sections—have been very limited. Neither infrared reflectography nor neutron induced autoradiography have proven to be practical, adequate visualization tools. Thus, although of fundamental interest in the understanding of a painting’s genesis, the underpainting has virtually escaped all imaging efforts. In this contribution we will show that 17th century underpainting may consist of a highly heterogeneous mixture of pigments, including copper pigments. We suggest that this brown pigment mixture is actually the recycled left-over of a palette scraping. With copper as the heaviest exclusive elemental component, we will hence show in a case study on a Portrait of an Old Man attributed to Rembrandt van Rijn how scanning macro-XRF can be used to efficiently visualize the underpainting below the surface painting and how this information can contribute to the discussion of the painting’s authenticity.     

Non‐destructive characterization of 17th century painted silk banner by the combined use of Raman and XRF portable systems

X‐ray fluorescence spectroscopy (XRF) and Raman spectroscopy analysis were performed to examine a 17th century painted silk banner in order to characterize the pigments and materials used. This complementary approach yields information on the elemental (XRF) and on the molecular composition (Raman) of the used compounds. The paint layer, ground layer under gilding, and gilding layer were investigated. For the studied object, vermilion (HgS), lead white (2PbCO₃ · Pb(OH)₂), red lead (Pb₃O₄), and aurichalcite ((Cu,Zn)₅(CO₃)₂(OH)₆) were found. The presence of silver and gold foils was confirmed. The techniques used in the analysis were portable, non‐destructive, and non‐invasive, which is very desirable when analyzing cultural heritage objects. The obtained results were used by the conservators to develop a showcase prototype for safe exhibition. Copyright © 2015 John Wiley & Sons, Ltd.     

Limitations of portable XRF implementations in evaluating depth information: an archaeometric perspective

Portable instruments that can perform non-destructive analysis techniques are of great importance due to their high applicability, which can extend beyond the controlled laboratory environment. Their importance has long been recognised in the archaeometric field where art historians, conservators and restorers perform analyses on art works without causing any damage and without the need to move the objects to specialized laboratories. The X-ray fluorescence (XRF) technique is a popular choice in the archaeometric field for in situ investigations with portable instrumentations. This enables qualitative (elemental analysis) and quantitative (chemical composition) information retrieval from the objects of interest. Quantitative analyses can be performed under the assumption that the sample is homogeneous and its surface material is the same as in the rest of the object. This work aims to expose various details, including the strengths and the weaknesses of typical XRF analyses in the case of surface alterations, focusing on portable implementations. The chosen approach will be in line with certain issues considered important in archaeometry; nevertheless the presented findings are valid beyond this. We will focus our discussion on two kinds of objects that can be found in the cultural heritage field: artefacts that had their surface material altered due to prolonged exposure to the environment and artefacts that have been gilded. Our work also includes a critically examined overview of relevant information available in the literature. The core of our analysis focuses on two main distinct cases, that of multilayer objects and that of bronzes. PACS 78.66.Bz; 78.70.En; 33.20.Rm     

Portable XRF as a valuable device for preliminary in situ pigment investigation of wooden inventory in the Trski Vrh Church in Croatia

The aim of this work was the investigation of pigments from the painted wooden inventory of the pilgrimage church of Saint Mary of Jerusalem in Trski Vrh – one of the most beautiful late-baroque sacral ensembles in Croatia. Being an object of high relevance for the national cultural heritage, an extensive research on the wooden polychromy was undertaken in order to work out a proposal for a conservation treatment. It consists mainly of two painted and gilded layers (the original one from the 18th century and a later one from 1903), partly overpainted during periodic conservation treatments in the past. The approach was to carry out extensive preliminary in situ pigment investigations using a portable XRF (X-ray fluorescence) device, and only the problems not resolved by this method on site were further analyzed using sophisticated laboratory equipment. Therefore, the XRF results acted as a valuable guideline for subsequent targeted sampling actions, thus minimizing the sampling damage. Important questions not answered by XRF (identification of organic pigments, ultramarine, etc.) were subsequently resolved using additional ex situ laboratory methods, primarily μ-PIXE (particle-induced X-ray emission) at the nuclear microprobe of the Rudjer Boskovic accelerator facility as well as μ-Raman spectroscopy at the Institute of the Academy of Fine Arts in Vienna. It is shown that by the combination of these often complementary methods a thorough characterization of each pigment can be obtained, allowing for a proper strategy of the conservation treatment. PACS  89.20.-a; 82.80.Ej; 82.80.Gk     

XRF spectrometer calibration for copper determination in wood

Method of X‐ray fluorescence (XRF) spectrometer calibration for copper analysis in wood was elaborated. Copper salt standard solutions for XRF measurements of liquid samples were prepared, and calibration curve of copper content dependence on impulse counts was determined. Specimens of pine wood (Pinus sylvestris L.) were treated with different solutions of copper‐based preservative (alkaline copper quarternary ammonium compound type) applying model low‐pressure preservation process. After treatment, wood specimens were sliced into six pieces, and exposed surfaces were analyzed using mapping option of XRF spectrometer. Then, wood from each analyzed surface was peeled with abrasive paper and dissolved in 65% nitric (V) acid. Copper content in solutions was determined using obtained calibration curve, and calibration dependence of copper content in wood on the average impulse counts on particular surfaces was calculated. Obtained results of copper content were consistent with values calculated on the basis of differences of samples weight before and after treatment. It confirms that proposed procedure is correct, and obtained equation may be used for unknown samples examination. Copyright © 2012 John Wiley & Sons, Ltd.     

Potentialities of XRF and EIS portable instruments for the characterisation of ancient artefacts

Non-destructive testing methods are very important tools for conservators and art historians to obtain valuable information about works of art without causing any or even local damage to them. Two successful case studies showing the noticeable potentialities of two analytical portable instruments employed in the characterisation of tangible cultural heritage are shown. The first example concerns the chemical characterisation via an X-ray fluorescence (XRF) portable instrument of the red decorative pigment and of the stone surface of the Capestrano Warrior (Archaeological Museum of Chieti, Italy), which is considered the most important Italic stone statue found in Italy. The second concerns the use of a portable electrochemical impedance spectroscopy (EIS) measurement system for the characterisation of the protective effectiveness of the paints on the railing of Palazzo Reale in Torino, Italy. PACS 68.55.Jk; 68.35.Dv; 68.37.Hk; 68.55.Nq; 81.05.Bx