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In situ, non-invasive and non-destructive analysis of important artworks and cultural pieces is largely important in art conservation science. Terahertz time-domain spectroscopy and imaging delivers these requirements but lacks a materials database with fundamental understanding of salient pigments, binders and substrates. In this study, the most important synthetic pigments, the copper phthalocyanines, are investigated through terahertz time-domain spectroscopy. The terahertz spectrum reveals a series of characteristic modes in a 0.1–3-THz range across 14 pigment samples. Identification and distinction of copper phthalocyanines' α, β and 𝜖 crystal polymorphs is demonstrated. This uniqueness within the terahertz regime is extended to two halogenated variants and a metal-free form. This invites the use of THz spectroscopy in investigation of contemporary artworks, post 1935, containing these pigments and promotes applications such as identifying fraudulent works of art. [ABSTRACT FROM AUTHOR]

Although medieval alabaster sculptures might appear white at present, they were colourful once, because painting and gilding the stone was an integral part of their production. This work presents the study of polychrome remnants on a selection of fourteenth century English alabasters, using multiple scientific methods (microscopy, spectroscopic and chromatographic techniques). The range of pigments identified include vermilion, red ochre, red lead, kermes, verdigris, copper resinate, azurite, lead white and carbon black. Some sophisticated decorative techniques were also observed, namely the application of translucent glazes on top of raised gilded motifs. The analysis was useful in understanding the degradation processes undergone by some materials, such as verdigris. The use of oil as binding medium for the application of the paint layers and a mordant gilding technique were determined. These findings yielded important clues towards the digital reconstruction of the original appearance of the polychrome surface, which is also presented here. [ABSTRACT FROM AUTHOR]

Zinc oxide, known as zinc white, is one of the principal white pigments developed in the 18th century and was used by the Impressionist painters. ZnO as artists’ pigment has occasionally been characterized by X-ray and ion beam techniques, but these studies are limited by the potential for visible radiation effect. Ion beam modifications of zinc oxide have extensively been investigated, but mainly for electronic and industrial applications. In this paper, we focus our investigation on ion beam modification of ZnO used as pigment. Two irradiation conditions have been used: an external 3 MeV proton micro-beam representative of PIXE analysis and 2 MeV H + and 1.2 MeV Au + beams in vacuum to investigate irradiation modifications in electronic and nuclear energy loss regimes. Ion beam modification was characterized by ex situ and in situ micro-Raman spectrometry and XPS. The results shows that IBA of zinc white can be carried out safely in historical paintings with low current and dose. [ABSTRACT FROM AUTHOR]

The discovery of an oil painting in seriously damaged condition with an important historical and a heterodox detail with possible origins in the late fifteenth century has afforded the opportunity for Raman microscopic analysis prior to its restoration being undertaken. The painting depicts a risen Christ following His crucifixion in a ‘noli me tangere’ pose with three women in an Italian terrace garden with a stone balustrade overlooking a rural landscape and an undoubted view of late-medieval Florence. The picture has suffered much abuse and is in very poor condition, which is possibly attributable to its controversial portrayal of a polydactylic Christ with six toes on His right foot. By the late sixteenth century, after the Council of Trent, this portrayal would almost certainly have been frowned upon by the Church authorities or more controversially as a depiction of the holy. Raman spectroscopic analysis of the pigments places the painting as being consistent chronologically with the Renaissance period following the identification of cinnabar, haematite, red lead, lead white, goethite, verdigris, caput mortuum and azurite with no evidence of more modern synthetic pigments or of modern restoration having been carried out. An interesting pigment mixture found here is that of the organic dye carmine and cinnabar to produce a particular bright red pigment coloration. Stratigraphic examination of the paint fragments has demonstrated the presence of an orange resin layer immediately on top of the canvas substrate, effectively rendering the pigment as a sandwich between this substratal resin and the overlying varnish. The Raman spectroscopic evidence clearly indicates that an attribution of the artwork to the Renaissance is consistent with the scientific analysis of the pigment composition.This article is part of the themed issue ‘Raman spectroscopy in art and archaeology’. [ABSTRACT FROM AUTHOR]

Raman spectroscopy is one of the few non-destructive techniques capable of identifying pigments in art works. Raman spectra contain powerful information that can be used to identify unknown compounds and their chemical structures. However, the analysis of spectral data comes with some difficulties, and therefore the spectral interpretation is not straightforward. Sometimes, there are very little differences in the spectral data concerning to specific identification objectives, for instance, in polymorphic discrimination or in the discrimination of natural and synthetic forms of certain pigments. Moreover, this discrimination is often performed manually so that the process can be repetitive, subjective and particularly time-consuming. The result is an increasing motivation to automate the identification process involved in the classification of pigments in paint. In this paper, we propose a system to automatically classify the spectral data into specific and well-known classes, i.e. reference classes. The proposal is based on a combination of chemometric techniques, which provides a powerful way to achieve spectral separability so that it is possible to discriminate between very similar spectra in an automatic way. In this regard, a decision-making algorithm was specifically developed to select the corresponding reference class with no user input, which was successfully validated using simulated spectra. The implemented methodology was used to classify Raman spectra of pigments commonly present in artist's paints in experimental cases, providing reliable and consistent results. Therefore, the presented system can play a good auxiliary role in the analysts' endpoint classification. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This study concerns the investigation of mortar layers and pigments of wall paintings from the Roman town of Emona (Ljubljana, Slovenia). Fragments of wall paintings consist of up to three preserved mortar layers. The mineralogical-petrographic compositions of the mortars were determined by means of optical microscopy and FT-IR spectroscopy. The investigated samples were divided into several groups based on similar thicknesses of the mortar layer, the binder colour and the composition of an aggregate. Furthermore, the results of mercury intrusion porosimetry showed that mortar layers consisting of carbonate grains exhibited lower porosity with respect to layers with mainly silicate grains, which is attributed to the angular shapes of carbonate aggregate. This is in accordance with the drilling resistance measurement system test (DRMS), confirming that layers with angular carbonate grains are harder than those with addition of rounded silicate ones, due to the good packing effect. The wall paintings were mainly executed using the fresco technique, while for some details secco was used. The identified pigments were red and yellow ochre, green earth, Egyptian blue, carbon black and lime white; all of them belonged to the so-called austere pigment, which is quite common in Roman wall paintings. [ABSTRACT FROM AUTHOR]

Despite considerable advantages of the method in the field of microanalysis of pigments, powder X-ray micro-diffraction has not yet been satisfactorily tested for correct and unambiguous discrimination of clay structures in colour layers of paintings and, eventually, for reliable quantitative analysis of their relative contents. To overcome this lack of knowledge, several sets of laboratory experiments with model mixtures and reference samples imitating real paint layers have been performed and general rules for proper discrimination of clay structures have been described. As an integral part of the research, clay–binder interactions were studied to avoid misleading interpretations. It was found out that various characteristic shifts of basal diffraction lines depend on the type of organic binder and the relative content of expandable layers in the clay structure. Based on these results, it was possible to differentiate pure smectites, interstratified illite/smectite structures and chlorites in paint and preparatory layers of actual paintings. The accuracy of quantitative microanalysis of clay minerals in mixtures with other minerals in Mid-European red earth pigments (typically containing kaolinite, illite, quartz, hematite, and anatase) was characterised by total bias values in the range of 3–10 wt.%. Finally, results were applied to differentiation of earth pigments of various provenances in grounds of Baroque paintings and Early Renaissance preparation layers for gilding. [ABSTRACT FROM AUTHOR]

Radiography in transmission mode is a well-established technique to visualize the internal structure of paintings. However, for many paintings the pictorial layer cannot be clearly visualized with conventional radiography because of interference from paint on the reverse, the material composition or the regular structure of supports or subsurface layers. Traditional lead white grounds in particular cause specific imaging problems not encountered with more modern white pigments such as zinc and titanium whites. A solution to this problem is radiography in emission mode. This study demonstrates and articulates those factors that can interfere with visualization of a painting's pictorial layer using transmission radiography as well as those that contribute to the effectiveness of emission radiography in visualizing such information. While emission radiography has been applied to the examination of paintings for over half a century, it is a cumbersome technique that is further complicated by the need to work under dim safelight illumination when X-radiographic film is used. Therefore, the use of computed radiography using storage phosphor imaging plates for emission radiography was also investigated. [ABSTRACT FROM AUTHOR]

The soundboards of seventeenth-century Flemish and French harpsichords, spinets, and virginals are frequently decorated with painted floral, animal, and ornamental motifs. Such decoration is very specific to this part of the instrument, and there are still many open questions regarding its aesthetics, as well as its technique and conservation. The few studies on the painting techniques and materials that exist to date have dealt with Flemish or with late eighteenth-century French instruments. Technical examination, using exclusively in situ techniques, was conducted on the soundboard paintings of the important corpus of seventeenth-century instruments in the collection of the Musée de la musique in Paris and showed regional specificities. Pigments were characterized using X-ray fluorescence, which in particular allowed qualitative discrimination between smalt pigments of different compositions. The state of conservation of the paintings could also be better understood, considering the mechanical deformations, stresses, and vibrations undergone by this specific painting support, a harpsichord soundboard. Future conservation protocols will thus require a delicate balance in order to preserve the double nature of such artefacts: musical instruments and works of art. [ABSTRACT FROM AUTHOR]

Expatriate artist Frances Mary Hodgkins (1869-1947) has been the focus of numerous art historical studies; however, very little is known about her painting practices. Trained as a watercolour artist, Hodgkins took up the use of other paint media in later life. She is most renowned for her work in oil and gouache, but in both cases the paint is applied very thickly, which has caused structural problems, particularly cracking and flaking. A technical study which included the examination of Hodgkins' papers and the analysis of paint was initiated in 2002, focusing on selected watercolours and gouaches from the Auckland Art Gallery Toi o Tamaki collection. It was intended to clarify many of the questions about her use of materials and her technique, which would be of benefit to conservators and curators. This paper presents the findings of the study and discusses aspects of Hodgkins' paint application and the implications for the conservation of her works. [ABSTRACT FROM AUTHOR]

Abstract: The application of total reflection X-ray fluorescence (TXRF) to the analysis of inorganic pigments used in five Albanian icons painted by Onufri Qiprioti, in the period from the end of 16th to the beginning of 17th century is presented. After removing the protective varnish with a solvent, a dry cotton-wool bud (Q-tip) was rubbed over the painted surface to collect the micro-samples. Samples, covering the main colors and their hues, were collected of each icon. A part of the small amount of the sample was transferred to a glass carrier and analyzed by TXRF. Main types of inorganic pigments used for different colors could be identified. The results indicate a palette which included white lead, calcium white, gold, orpiment, yellow and red ochre, vermilion, red lead; a cooper based green pigment (malachite or verdigris) and smalt. [Copyright &y& Elsevier]

Raman spectroscopy is an analytical technique, which is gaining attention as a molecular technique for the investigation of objects of art. Especially the non-destructive properties of the method make this application suitable for the in situ analysis of artefacts. However, although using mobile, fibre optics Raman instrumentation for this type of research seems to be straightforward, some practical obstacles may hamper the investigation. In this paper, pitfalls and solutions are described when applying a dedicated spectrometer to the analysis of mediaeval wall paintings. It is shown how some practical problems may be overcome, and the results of the analysis are presented. Although the mediaeval wall paintings from the chapel of the castle of Ponthoz are well-preserved, still some interesting degradation phenomena could be observed: the identification of a black degradation product, likely to be meta-cinnabar, a degradation product of the red pigment vermilion (HgS); the formation of gypsum (CaSO4·2H2O) as a weathering product of calcium carbonate (CaCO3); the observation of copper(II)hydroxychlorides. [ABSTRACT FROM AUTHOR]

Abstract: Raman spectroscopy has been applied to the examination of wall painting fragments from the archaeological site of Ek’Balam (Yucatán, Mexico). Thirty-three samples have been studied, all originating from room 23 of the Acropolis, and being representative of the painting technique at Ek’Balam during the late Classic Maya period. Several pigments such as haematite, calcite, carbon, cinnabar and indigo were identified in these samples. The latter pigment was presumed to be present as ‘Maya blue’, which is an intercalation product of indigo and palygorskite clay. The observed Raman spectra are reported and some band assignments have been made. This survey is the first Raman spectroscopic examination of a whole set of pigments in archaeological Maya wall painting fragments. [Copyright &y& Elsevier]

The combination of PIXE, RBS and PIGE proves ideal for non-destructive overall analysis of reverse paintings on glass. Simultaneous PIXE–RBS studies assist to clarify the thin-layered pigment arrangements of details painted on the reverse of the glass pane. In a second measurement, the spectra of both PIGE–PIXE taken from the pure glass front side inform on the individual glass type. This complete perception of corresponding unique objects is important and valuable regarding the knowledge of special painting techniques and the necessity of preventive conservation. [Copyright &y& Elsevier]