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The preparation of mock-ups in heritage science studies represents a valid alternative for investigation purposes, avoiding extensive sampling of cultural heritage objects. This work presents for the first time the successful preparation of three dimensional (3D) mock-ups made of celluloid, considering a combination of historical industrial production strategies and small-scale lab facilities. Prefabricated transparent celluloid sheets were acquired and then shaped through compression molding for creating mock-ups with 3D geometries. These reflected common and representative shapes encountered in the collection of the Deutsches Museum. Visual inspection of the mock-ups allowed determining the best compression molding conditions. Attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) confirmed the absence of molecular heterogeneity due to the processing method. Artificial aging of the mock-ups was conducted to reach degradation states comparable with naturally aged objects. ATR-FTIR investigation offered first insights into the induced artificial degradation. Ion chromatography (IC) and gel permeation chromatography (GPC) analyses allowed to assess the extent of the artificial aging of the celluloid mock-ups and confirmed the occurrence of loss of camphor, denitration, and main chain polymer scission, the latter being the predominant decay path. The comparison with historical objects highlighted that the mock-ups are representative of moderately aged artifacts. As such, this study paves the way for implementing moderately aged celluloid 3D mock-ups in heritage science research, enabling in-depth testing for the scope of conservation.

Funding Information: This work was co-funded by the research project ‘Plastic Paints in Art: the impact of manufacturing processes on their long-term stability’, financed by national funds from FCT/MCTES ( IF/00653/2015/CP1293/CT0005 as well as UIDB/50006/2020 , UIDB/00286/2020 , and UIDP/00286/2020 ). We would like to thank Anthony J. Baragona (Institute of Conservation and Restoration, University of Applied Arts, Vienna, Austria) for helping with the English corrections. Publisher Copyright: © 2022 This research explores the use of different pyrolysis-based techniques for studying the chemical composition of vinyl acetate (VAc) based emulsions widely used in modern-contemporary art and contributes to the understanding of their composition by the detection of different monomers and additives. For this purpose, six different commercial VAc-based emulsions from the early 21st century were analyzed for the first time by single-shot (SS) and double-shot (DS) pyrolysis – gas chromatography / mass spectrometry (Py-GC/MS). The results obtained were compared, and highlight the advantages of DS in comparison to SS for the analysis of VAc-based emulsions. Several different components assigned to plasticizers, surfactants, intermediates, and antioxidant families, were detected, mainly by the thermal desorption step of DS. The information gained by this research enriches the knowledge of the formulation of VAc-based emulsions, by considering for the first time a large variety of them. Moreover, it also points to the importance and the potential of DS Py-GC/MS for investigating these materials, which have been rarely explored with this technique. publishersversion published

Lighting is a critical component in a museum environment because, together with temperature, relative humidity and pollutants, it is one of the damaging factors able to produce long‐term, cumulative and irreversible photodegradation processes. To correctly preserve artworks, limiting illuminance and exposure is recommended, allowing on one side the preservation of the object, but on the other limiting the display of the object, especially for sensitive materials. The aim of this research was to develop, evaluate and compare a new lighting method for paintings and other cultural materials to improve the experience of the objects whilst reducing the risks from exposure. The idea is based on the use of selective chromatic light where the component of the spectrum absorbed by the materials is removed. This absorption is the principal cause of photodegradation. The proposed lighting system can be obtained by combining different types of projection systems together with filtering using an appropriate light source. Six methods of light projection have been compared for two mock-ups simulating real artworks with high and medium light sensitivity. The efficiency of illumination increased from 30% to 111% compared to standard lighting systems. Light stability tests were additionally performed, finding reduced colour changes compared to traditional lighting systems.

The identification of colorants in historic plastics is a methodological and analytical challenge. Although deformulation is performed by the plastics industry, in the case of historical objects, sampling is often impossible, and in situ protocols are needed. The accurate identification of colorants provides insights into historical plastic formulations, supports planning of conservation studies, and critical data for objects that already exhibit color change (e.g. fading). Indeed, colorants may degrade following exposure to light, and color changes have been reported for plastic objects. The analysis of colorants remains a challenge, and microsampling is usually required. Successful identification of red pigments from thirty historical plastics is reported following a new in situ analytical protocol based on Raman microscopy. Information about other pigments, fillers and plastic polymers are reported. Fading has been observed in the historical plastic objects containing Pigment Red 53.

Celluloid artifacts are known by conservation professionals to be prone to degradation, threatening their own integrity and that of nearby heritage collections. Celluloid alteration can have a heterogeneous nature, and this research topic is still in its infancy for heritage science. This article investigates degradation gradients, both along depth and width, of artificially aged celluloid sheets, and compares them to three-dimensional (3D) historical objects with the aim of gaining a better insight into the nature and evolution of their decay. ATR-FTIR was used to systematically study different sampling points of the artificially and naturally aged specimens and allowed us to recognize better-preserved surfaces and more deteriorated cores. ATR-FTIR was found suitable for assessing the molecular changes induced by degradation, particularly denitration and formation of carbonyl-containing degradation products in severely aged specimens. Even though the severely artificially aged sheets displayed unusual alteration phenomena, they present a degradation gradient similar to the one observed for the naturally aged 3D objects under study. This research underlines that sampling at different depths and/or widths is relevant for characterizing the heterogeneity of degraded celluloid, and further investigation with chromatographic techniques would greatly benefit the understanding of the complex degradation of celluloid artifacts.

Light is a determining factor in the discoloration of plastics, and photodegradation processes can affect the molecular structures of both the polymer and colorants. Limited studies focused on the discoloration of heritage plastics in conservation science. This work investigated the discoloration of red historical polyethylene (PE) objects colored with PR 48:2 and PR 53:1. High-density and low-density PE reference polymers, neat pigment powders, and historical samples were assessed before and after accelerated photoaging. The applied methodology provided insight into the individual light-susceptibility of polyethylenes, organic pigment lakes, and their combined effect in the photoaging of historical plastic formulations. After light exposure, both PE references and historical samples yellowed, PR53:1 faded, and PR 48:2 darkened, however, both organic pigments faded severely in the historical samples. This highlights the role played by the plastic binder likely facilitating the pigment photofading. Fourier transform infrared spectroscopy and mass spectrometry techniques—EGA-MS, PY-GC/MS, and TD-GC/MS—were successfully employed for characterizing the plastic formulations and degradation. The identification of phthalic compounds in both aged β-naphthol powders opens new venues for studies on their degradation. This work’s approach and analytical methods in studying the discoloration of historical plastics are novel, proving their efficacy, reliability, and potentiality.

Plastics have been increasingly used to create modern and contemporary art and design, and nowadays, museum collections hold numerous objects completely or partially made of plastics. However, the preservation of these materials is still a challenging task in heritage conservation, especially because some plastics show signs of degradation shortly after their production. In addition, different degradation mechanisms can often take place depending on the plastic composition and appropriate environmental and packaging conditions should be adopted. Therefore, methods for in situ and rapid characterization of plastic artifacts’ composition are greatly needed to outline proper conservation strategies. Infrared (IR) spectroscopy, such as attenuated total reflection Fourier transform infrared spectroscopy (ATR FT-IR), is a well-established method for polymeric material analysis. However, ATR FT-IR requires an intimate contact with the object, which makes its application less appropriate for the in situ investigation of fragile or brittle degraded plastic objects. Mid-FT-IR reflectance spectroscopy may represent a valid alternative as it allows in situ measurements with minimum or even no contact, and IR data can be acquired rapidly. On the other hand, spectral interpretation of reflectance spectra is usually difficult as IR bands may appear distorted with significant changes in band maximum, shape, and relative intensity, depending on the optical properties and surface texture of the material analyzed. Presently, mid-FT-IR reflection devices working in external reflection (ER FT-IR) and diffuse reflection infrared Fourier transform spectroscopy (DRIFTS) modes have been used in cultural heritage research studies. As the collected vibrational information depends on the optical layout of the measuring system, differences between ER FT-IR and DRIFT spectra are thus expected when the same polymer is analyzed. So far, ER FT-IR and DRIFT spectroscopy have been individually explored for the identification of plastic objects, but comparative studies between the application of two reflectance FT-IR modes have not been presented yet. In this work, the use of two portable FT-IR spectrometers equipped with ER FT-IR and DRIFTS modes were compared for plastics identification purposes for the first time. Both references of polymeric materials and historical plastic objects (from a Portuguese private collection) were studied and the differences between ER FT-IR and DRIFT spectra were discussed. The spectra features were examined considering the two different optical geometries and analytes’ properties. This new insight can support a better understanding of both vibrational information acquired and practical aspects in the application of the ER FT-IR and DRIFTS in plastic analysis.

Decades of technological advances in instrumental analysis have transformed many techniques from laboratory innovations to customary analytical tools with increasing applicability to the study of cultural heritage objects. In particular, enduring research in the field of miniaturization has given rise to new generations of mobile, portable, and handheld spectrometers that have deeply altered the way in which scientists approach the analysis of materials in artifacts of archaeological, historical, and artistic significance.

Colorants are present in trace concentration in objects made of plastic and their identification is a methodological and analytical challenge. In conservation, the identification of colorants may allow a better understanding of colorant degradation (such as color change and fading) and provide information about the historical development, production and processing of plastics. Although micro-destructive analytical protocols are well established for the analysis of colorants, in cultural heritage, where in situ methodologies are preferred and, in some cases, mandatory, new approaches are greatly needed. In this work, an in situ multi-analytical approach is used to specifically study inorganic cadmium-based pigments that were commonly used for coloring plastics during the 20th c. First introduced as vivid artists’ pigments, cadmium-based additives were used for coloring plastics because of their exceptional performance properties. Eighteen colored polymethyl methacrylate (PMMA) samples, produced in the second half of the 20th c. by the company Plasticos do Sado (Portugal), were studied with a combination of optical microscopy, colorimetry, UV–Vis-NIR diffuse reflectance, laser-induced photoluminescence, vibrational (µ-Raman) and elemental (µ-EDXRF) spectroscopies. On the basis of complementary data, the chemical composition of most of the coloring agents employed in the acrylic samples were identified without any micro-sampling.

Naphthol reds are historical pigments widely found in cultural heritage, characterized by 1-arylhydrazone-2-naphthol basic skeleton. Little is known about their degradation mechanisms, and this knowledge is essential for their long-term preservation. In this research, for the first time, the photodegradation quantum yields (ΦR) were calculated for a series of pigment reds selected based on published literature, in order to evaluate the effects of the electron-withdrawing and donating groups present in C(4′), in particular the effect of sulfonate groups on the stability of these compounds. ΦR values in homogeneous media, ranging from 3 × 10−6 to 4 × 10−5, are difficult to obtain in these systems, but provide the quantification of the stability of naphthol reds. One of the main conclusions is that the sulfonate groups have a stabilizing effect and that the keto forms are generally more stable. Another important piece of information is that the solvent, and as such the medium predictably, has a major impact on stability. For Sudan I and Orange II irradiation was also carried with a xenon source (λirr ≥ 300 nm), allowing characterizing the main degradation products by HPLC-DAD-MS and UHPLC-HRMS. For the dyes characterized by higher ΦR, extensive degradation was observed with the formation of volatile compounds as phthalates.

Portuguese Science Foundation through three research projects and three Ph.D. Grants, including the three awarded to Paula Nabais, Rita Aranjo and Eva Mariasole Angelin (CORES Ph.D. programme PD/00253/2012: PD/BD/105895/2014, SFRH/BD/52314/2013 and PD/BD/114412/2016). FCT/MCTES (UID/QUI/50006/2019). Support was also given by the Calouste Gulbenkian Foundation award 'Estimulo Investigacao 2016' (146301). Ministerio de Economfa, Industria y Competitividad del Gobiemo de Espana (MINECO-EAI/FEDER) for project IMAN (Investigacion y analisis para el conocimiento y la preservacion de un patrimonio documental: los manuscritos andalusies), HAR2016-77482-R. The conservation of Islamic manuscripts in the Fondo Ka'ti created the opportunity to study the organic red colourants applied in five manuscripts, which include a Koran (1198), a theology treatise (14 th c.), a book of poems from Al-Sarishi (15 th c.), a biography of the Prophet (1468) and manuscript 19 (1485). These dark red colours were characterized using fibre optic reflectance spectroscopy (FORS-VIS), microspectrofluorimetry and infrared spectroscopy (microFTIR). Microspectrofluorimetry detected the presence of a lac dye chromophore in all the manuscripts studied and ascribed it to specific medieval recipes for three of the manuscripts. This was based on the very good matches obtained with our database of paint reconstructions that were prepared according to medieval technical sources; the dark reds found in the Koran compared very well with the recipe ‘to make red ruby from lukk’ from Ibn Bādīs text (11 th c.); the brighter reds applied in the book of poems and in the biography of the Prophet, with recipe 113 from the Paduan manuscript (16 th c.). MicroFTIR completed the characterization of the paint formulation, identifying the proteinaceous nature of the binding media as well as the fillers. It also showed the presence of oxalate compounds, possibly, resulting from the binding media degradation, a mark of the recent and dramatic history of these books. Finally, these red dyes were successfully compared to lac dye colours previously characterized in 12 th -13 th c. Portuguese manuscript illuminations. From Mali to Iberia, tracing the rich diversity of a precious heritage legated by medieval Arabic culture. authorsversion published

The absorption of light gives a pigment its colour and its reason for being, but it also creates excited states, that is, new molecules with an energy excess that can be dissipated through degradation pathways. Photodegradation processes provoke long-term, cumulative and irreversible colour changes (fading, darkening, blanching) of which the prediction and prevention are challenging tasks. Of all the environmental risks that affect heritage materials, light exposure is the only one that cannot be controlled without any impact on the optimal display of the exhibit. Light-induced alterations are not only associated with the pigment itself but also with its interactions with support/binder and, in turn, are further complicated by the nature of the environmental conditions. In this Minireview we investigate how chemistry, encompassing multi-scale analytical investigations of works of art, computational modelling and physical and chemical studies contributes to improve our prediction of artwork appearance before degradation and to establish effective preventive conservation strategies.

The identification of artistic materials represents a fundamental step in supporting the conservation of cultural heritage objects. The importance of their appropriate characterization is particularly relevant in modern-contemporary art, since they could be affected by the occurrence of rapid changes in chemical formulation over time. This paper focuses on an investigation of a series of contemporary blue-green commercial acrylic paints constituted of spinel pigments, using non-invasive spectroscopic techniques. The spectroscopic and color measurements obtained make it possible to characterize the acrylic paints under investigation and to compare the results obtained with those reported in the literature and in spectral databases. To be more precise, the proposed UV-vis-NIR reflectance spectroscopic technique was sensitive enough to characterize the acrylic paints according to their d-d ligand field and the charge transfer (CT) electronic transitions involved in the spinel structures. In addition, an overview of this class of inorganic pigments is also given.