Paint Layers Research Articles

Stratigraphic mapping of paintings by multispectral reflectography

Despite recent technological advances, it is currently not possible to uniquely and noninvasively measure the micrometric thickness of pictorial layers in paintings. The presence of optically opaque materials (pigments) severely limits the detection capability, as it hinders the penetration of the probe's near-infrared radiation, typically employed for this purpose. In our previous work, we explored the possibility of using diffuse reflectance spectroscopy (DRS) to achieve stratigraphic information about painting materials. We showed that the thickness of pictorial layers can be quantified by the intensity of the spectral reflectance factor measured at a given wavelength in the infrared, i.e., an easily detectable spectral feature. In the present work, we extend the previously proposed method by applying multispectral reflectography to measure new ad hoc prepared pictorial samples and a mock-up simulating a Mondrian painting. We thus demonstrate that it is possible to obtain 2D and 3D stratigraphic maps of the pictorial layer over large areas with the same measurement time and spatial resolution as multispectral scanning reflectography.

Combined macro X-ray fluorescence (MA-XRF) and pulse phase thermography (PPT) imaging for the technical study of panel paintings

Museum staff usually relies on a proven combination of X-ray radiography (XRR) and infrared reflectography (IRR) to study paintings in a non-destructive manner. In the last decades, however, the research toolbox of heritage scientists has expanded considerably, with a prime example being macro X-ray fluorescence (MA-XRF), producing element-specific images. The goal of this article is to illustrate the added value of augmenting MA-XRF with pulse phase thermography (PPT), a variant of active infrared thermographic imaging (IRT), which is an innovative diagnostic method that is able to reveal variations between or in materials, based on a different response to minor fluctuations in temperature when irradiated with optical radiation. By examining three 16th- and 17th-century panel paintings we assess the extent in which combined MA-XRF and PPT contributes to a better understanding of two commonly encountered interventions to panel paintings: (a) Anstückungen (enlargement of the panel) or (b) substitutions (replacement of part of the panel). Yielding information from different depths of the painting, these two techniques proved highly complementary with IRR and XRR, expanding the understanding of the build-up, genesis, and material history of the paintings. While MA-XRF documented the interventions to the wooden substrate indirectly by revealing variations in painting materials, paint handling and/or layer sequence between the original part and the extended or replaced planks, PPT proved beneficial for the study of the wooden support itself, by providing a clear image of the wood structure quasi-free of distortion by the superimposed paint or cradling. XRR, on the other hand, revealed other features from the wood structure, not visible with PPT, and allowed looking through the wooden panels, revealing e.g. the dowels used for joining the planks. Additionally, IRR visualised dissimilarities in the underdrawings. In this way, the results indicate that PPT has the potential to become an acknowledged add-on to the expanding set of imaging methods for paintings, especially when used in combination with MA-XRF, IRR and XRR.

EXTRACTION OF PAINT LOSS IN ANCIENT MURALS BASED ON 3D RESIDUAL NEURAL NETWORK

Abstract. The ancient murals of Qutan Temple in Qinghai Province have a very serious loss of paint. Moreover, the main components of the base color paint layer in the paint loss area and the white patterns in the murals are both calcified, which are similar in color and spectral features. Thus, it is difficult to distinguish them by only using spectral features. A method of paint loss area extraction based on 3D residual network with multi-scale feature fusion is proposed. Firstly, the hyperspectral images with paint loss regions were collected by hyperspectral images. They are pre-processed to establish the training data set. Secondly, 3D residual network models are constructed using 3×3×3, 3×3×5 and 5×5×3 convolution kernels to realize the extraction and fusion of spatial and spectral features at different scales of hyperspectral images. The produced mural hyperspectral dataset is used for network training to obtain the prediction model. Finally, the hyperspectral images are input into the trained model to achieve the extraction of paint loss. After comparing different methods, the experimental result shows that the proposed method can improve the extraction accuracy of mural paint loss and serve as a reference for other deteriorations extraction.

Quantitative spectroscopic characterization of laser-induced effects on oil paint films using 213, 266, or 2940 nm

Removal of aged varnish layers from easel paintings is a challenging task requiring methodologies capable of preventing any alteration of the underlying painted surface. Laser-ablation approaches using the fourth and fifth harmonics of a Q-Switched Nd:YAG (266 and 213 nm, 15 ns) and Free-Running Er:YAG laser (2940 nm, 160 µs pulses) can allow for very thin removal rates but their discrimination of the underlying paint film and self-termination potential are very limited. Thus, there is a need to develop suitable analytical methods for promptly identifying the possible occurrence of any undesired effect on the paint layer beneath the varnish, which is intentionally or unintentionally irradiated during the laser thinning treatment. Such side effects depend on the irradiation parameters and the specific material features of the pictorial film. Linseed oil paint models were prepared using lead white, vermilion, chrome yellow, ultramarine, Prussian blue and zinc white. Two distinct pigment volume concentrations (PVC) were used to investigate the dependence of the laser-induced alterations on oil binder volume ratio: low PVC (gloss paint) and high PVC (matte paint). After determining threshold exposure limits for each laser wavelength, laser-induced effects slightly above the threshold fluence were qualitatively and quantitatively assessed using FTIR and µ-Raman spectroscopies. Results showed that IR-reflectance bands of glossy and matte films exhibited appreciable shifts and distortion upon laser irradiation while reductions of the signal-to-background ratio were observed in µRaman spectra. The developed method, based on the processing of a number of spectral acquisitions, enabled for the first time the quantitative assessment and comparison of the corresponding undesired laser-induced effects in the outermost painted layer.

NIR reflective Paints as an Alternative for Sustainable Façade Renovation

Several studies of infrared reflective materials used on opaque envelopes have shown that their application can reduce the surface temperature and the cooling energy needs of buildings and help mitigate the urban heat island effect. Some of these studies were carried out by incorporating near-infrared (NIR) reflective materials on new buildings or as part of new construction systems, considering that one of the simpler and most used façade renovation methods is repainting. In a repainting process, the reflectance could change since the reflectance depends on the interaction between the reflective layer and the substrate. A study was carried out on the reflectance of paints with NIR reflective properties applied on the finishing coat of external thermal insulation composite systems (ETICS), simulating a façade renovation. A black NIR reflective paint was applied in one layer over the existing finishing coat of two ETICS samples: one with a grey mortar colour and another with a conventional black colour. A second configuration was considered by adding an intermediate layer of regularisation with white colour. Traditional black colour and the mortars were applied on a transparent acrylic base as a reference. The samples were assessed with a modular spectrophotometer to assess the total and NIR reflectance and the colour coordinates on the CIELab space. The results showed that the reflectance and colour of the new layer are independent of the colour or type of the first layer in the case of conventional paint. Conversely, the substrate affects the NIR paint performance, where a lighter substrate can help improve the reflectance but can also lead to a more significant colour change. Likewise, the results of the paint over a new white layer resulted in a lower reflectance compared to the reflectance of a single paint layer.

Forensic analysis of white automotive paint of same manufacturer with Raman spectroscopy and chemometrics

AbstractDiscriminating paints of the same color has always been a challenge in automotive paint examination. The process is even more difficult when these paints originate from the same manufacturer and color. Raman spectroscopy is an effective and non‐destructive method that is commonly used to differentiate automotive paint. This method is often used to provide a reliable information about pigments and extenders contained in topcoats and is barely used to examine other layers of paints. In this study, A total of 54 white automotive paints from one single manufacturer (Volkswagen) were prepared and analyzed by Raman Spectroscopy. Each layer of the samples was measured in order to evaluate if Raman spectroscopy can provide good discrimination power. Statistical methods were used to characterize and classify these samples. Correlations between paint characteristics and discriminating factors (such as model, topcoat color code, production year, and assembly plant) were also investigated to get a deeper understanding of automotive paints.

A Study of Pigment, Adhesive, and Firing Temperature in Pottery Figurines Excavated from the Tomb of Qibi Ming, China

Some painted pottery figurines were excavated from the tomb of Qibi Ming of the Tang Dynasty. A series of analytical techniques were employed to understand the craftsmanship of these painted pottery figurines. The pigment, cross-section, adhesive, and firing temperature were analyzed using microscopy (OM), energy X-ray fluorescence spectrometry (EDX), micro-Raman spectroscopy, pyrolysis–gas chromatography–mass spectrometry (Py-GC/MS), and a dilatometer (DIL). The results demonstrated that the surface of the pigment layers had degraded to different degrees. The pigment particles were litharge, gypsum, malachite, cinnabar, hematite, minium, white lead, and carbon black. The cross-sectional images show that the painted layer of figurines 10-0966 and 10-0678 included a pigment layer and a preparation layer. The preparation layer of both pigments was lead white. Animal glue was used as an adhesive. The firing temperature of the pottery figurines was likely 1080 °C. This study can provide more accurate information with regard to the composition of the raw materials utilized in the making of these artifacts and support the selection of appropriate substances for the purposes of conservation and restoration of the painted pottery figurines.

Tailoring the properties of poly(vinyl alcohol) “twin-chain” gels via sebacic acid decoration

HypothesisThe development of gels capable to adapt and act at the interface of rough surfaces is a central topic in modern science for Cultural Heritage preservation. To overcome the limitations of solvents or polymer solutions, commonly used in the restoration practice, poly(vinyl alcohol) (PVA) “twin–chain” polymer networks (TC-PNs) have been recently proposed. The properties of this new class of gels, that are the most performing gels available for Cultural Heritage preservation, are mostly unexplored. This paper investigates how chemical modifications affect gels’ structure and their rheological behavior, producing new gelled systems with enhanced and tunable properties for challenging applications, not restricted to Cultural Heritage preservation. ExperimentsIn this study, the PVA-TC-PNs structural and functional properties were changed by functionalization with sebacic acid into a new class of TC-PNs. Functionalization affects the porosity and nanostructure of the network, changing its uptake/release of fluids and favoring the uptake of organic solvents with various polarity, a crucial feature to boost the versatility of TC-PNs in practical applications. FindingsThe functionalized gels exhibited unprecedented performances during the cleaning of contemporary paintings from the Peggy Gugghenheim collection (Venice), whose restoration with traditional solvents and swabs would be difficult to avoid possible disfigurements to the painted layers. These results candidate the functionalized TC-PNs as a new, highly promising class of gels in art preservation.

New Data on Orange Mineral Pigments in the Works of the Nevyansk School of Icon Painting

The purpose of this paper is to investigate an unusual technological feature of the icons of the Old Believer mining and metallurgical Urals, that consists in the use of the minerals crocoite and realgar as artistic pigments. During the technological examination of sixty-two Nevyansk icons of the 18th – 19th centuries in the State Research Institute for Restoration (GOSNIIR) in 2019–2023, realgar was found in twenty-two icons, while crocoite was detected in eleven, which proves the widespread usage of these minerals in Ural icon painting. Chemical analysis of the paint layer samples from the icons was carried out using a set of analytical methods such as polarized microscopy, energy-dispersive X-ray spectroscopy, micro-FTIR and Raman spectroscopy. It should be noted that both mineral pigments are rare not only for Russian painting, but also for late Russian icon painting of other artistic centers and schools. Thus, it can be assumed that realgar was introduced to the Ural masters as an imported paint from Western Europe under the name Rauschgelb / Rusgeel, where it was in high demand among painters between the 16th and 18th centuries. It is also possible that it could have been brought to Russia, to the Urals, from China or Central Asia, where its large deposits are located. However, the appearance of crocoite in Nevyansk icons is undeniably due to the discovery and development of its deposits in the Middle Urals. Both minerals were first applied in Nevyansk icons in the second half of the 18th century (the lower chronological boundary of crocoite use is the first half of the 60s of the 18th century). Apparently, in the 19th century they gradually ceased to be in common use among the Ural icon painters.

Graphene Oxides as Epsilon‐Near‐Zero Platforms Operating in Terahertz Frequency Range

AbstractEpsilon‐near‐zero (ENZ) materials, with their unique light manipulation capabilities, have fascinating applications such as cloaking, super‐resolution imaging, energy harvesting, and sensing. Herein, free‐standing graphene oxide films are fabricated whose dielectric constant can be engineered by thermal reduction, resulting in ENZ characteristics at the transition between insulating and metallic phases. The ENZ frequency is found to be 0.4–0.5 THz under an annealing temperature of 200 °C, whereas another ENZ phase appeared at 360 °C. ENZ film can be transferred to curved metal surfaces, serving as superabsorbers that suppress wave reflection from underneath metal surfaces. Hyper‐resolution in nondestructive THz imaging is also possible, owing to superior beaming. Spatial resolution is improved two‐fold by adding the ENZ film, even when the metal pattern is enclosed by a paint layer. Lastly, hybrid sensors are developed by incorporating the meta‐pattern on the free‐standing ENZ substrate. The energy splitting of metamaterial resonance originating from the coupling with ENZ mode is observed. Hybridized devices have proven effective in detecting microorganisms with a low refractive index, owing to the unique dielectric configuration offered by ENZ material. Using the novel ENZ platform, a 15‐fold improvement in microbial sensitivity is achieved compared with the conventional sensors.

X-ray-based examination of artworks by Cy Twombly: art technology and condition of the ‘Original Sculptures’

What are Cy Twombly’s sculptures made of? This article presents an overview of a non-destructive examination conducted on three sculptures by American artist Cy Twombly (1928–2011) as part of an art-technological research project at the Doerner Institut in Munich. The artworks are part of the collection of the Brandhorst Museum and belong to Twombly’s series of so-called ‘Original Sculptures’: assemblages of individual found objects, which the artist covered and modified with layers of plaster and white paint. To develop a long-term preservation strategy, the research focused on understanding the materials and construction methods used in Twombly's sculptures. In collaboration with the Chair of Non-Destructive Testing at the Technical University of Munich, the artworks were inspected using X-ray radiography and computed tomography. The results showed that Cy Twombly used various everyday objects made from wood, plastics, metal, and paper/cardboard to build the assemblages. Unexpectedly, the examinations revealed that the individual parts are solely held together by the coating of plaster and paint, lacking additional mechanical connections. The overall structure thus proved to be very fragile and highly sensitive to physical stresses, whether due to handling, transport, or strains in the microstructure caused by climatic fluctuations. Since little was known about Cy Twombly´s choice of materials and manufacturing details, the results offer valuable insights into the overall artistic process and decision-making of one of the most influential artists of the 20th/twenty-first centuries. Conservators can use the art-technological findings to monitor the sculptures ‘condition and develop or adapt long-term preservation strategies, including aspects such as ambient climatic conditions and handling storage and transport specifications. In addition, the knowledge generated can be used for further research on the specific materials and transferred to other artworks by Cy Twombly.

Crack cause analysis of a third stage stator vane of the low-pressure compressor in an aeroengine

A cracked third stage stator vane of the low-pressure compressor was found during a major overhaul of an aeroengine. The crack originated from a corrosion pit located on the arc transition between the leading edge and the upper edge plate. The finite element analysis results demonstrated the arc transition was the region with the large von-Mises stress under the wake excitation. The cleavage-like fracture and fatigue striations predominated throughout the fracture surface, indicating it was a pit-related fatigue crack. Meanwhile, Metallographic examination discovered most of corrosion pits beneath the bulging or peeling of the paint layer were distributed on the leading edge and the concave side. Moreover, the composition and phase identification results showed that the corrosion products included sulfate and alumina. Considering the pitting corrosion products and outdoor environment of the aircraft downtime, it was inferred that the cracked stator vane suffered from atmospheric corrosion.

An analytical Study of the Paint Layer of the Chalice Chairs’ Icons from the 19th Century A.D. in the Virgin Mary Church in Haret Zuwaila – Cairo

An analytical Study of the Paint Layer of the Chalice Chairs’ Icons from the 19th Century A.D. in the Virgin Mary Church in Haret Zuwaila – Cairo

DATING OF WOODEN HERITAGE OBJECTS IN THE GLIWICE 14C AND MASS SPECTROMETRY LABORATORY

ABSTRACT We present case studies on three objects of high importance for cultural heritage in southern Poland, dated in years 2018–2022 at the Gliwice 14C and Mass Spectrometry Laboratory with radiocarbon (14C) and dendrochronology methods. The first was a richly ornamented wooden cane, discovered during excavations on the market in Bytom city. The cane can be associated with medieval court proceedings. The archaeological context indicates the 13th century AD, and the 14C result corresponds perfectly with this time, confirming that it is the oldest object of this type in Poland. The second was a 4-m-tall oak column from St. Leonard Church in Lipnica Murowana, a UNESCO heritage site. The local story said it was previously devoted to Światowid, a pagan deity. Our analysis excluded the pre-Christian age, as the tree was felled no earlier than the late 15th century, which is in agreement with historical records. The third was a wooden Saint Lawrence Church in Bobrowniki. The presbytery was covered with up to five layers of polychromic paintings, some of high artistic value. We dated three samples from the original wooden board, and by wiggle-matching, the calibrated age interval was narrowed to 1731–1754 cal AD.

Recycling of Magnesium Alloy Scrap by Remelting and Chemical De-coating Process

The growing demands of magnesium (Mg) based materials had risen new challenges related to disposal of unused parts and a huge amount of waste made by such metals. Attempts to recycle the scrap of these materials through remelting had become one of the preferred choices. However, a series of preliminary steps should be carried out to reduce the impurities as well as to maintain the quality of the casted ingot, for instance, by applying de-coating for removing paints or coating substrates at the scrap surface prior to remelting. In this research, the effects of chemical reagent de-coating on the properties of ingot obtained from recycling Mg scrap were studied. A commercial paint removal liquid was preferred as the reagent for removing paint layers over the Mg scrap surface. The de-coated scrap was then remelted in a conventional furnace with NaCl powder as the fluxing layer. The results of this study noticed the importance of chemical de-coating process to reduce the impurity contents in the ingot which might be originated from the coating or paint substrates covering the Mg scrap. Meanwhile, the density and hardness of the Mg ingot processed without de-coating were obviously higher than that had been cleaned previously with paint removing agent.

Droplet absorption and spreading into thin layers of polymer hydrogels

From biological tissues to microactuators and absorption of solvents into layers of paint, macroscopically non-porous materials with the capacity to swell when in contact with a solvent are ubiquitous. In these systems, owing to strong solid–fluid interactions, chemically driven flows can yield large geometric changes. We study experimentally and theoretically the canonical problem of the swelling of a thin hydrogel layer by a single water drop. Using a bespoke experimental set-up, we observe fast absorption leading to a radially spreading axisymmetric blister. We use a fully three-dimensional linear poroelastic framework with nonlinear kinematic equations to obtain governing equations, which we then reduce with thin-layer scalings to a one-dimensional nonlinear diffusion equation for the evolution of the blister geometry. In the limits of large and small deformations, the evolution of the blister characteristic height and radius are self-similar, following power laws in time. Our experimental measurements show that the evolution of the blister is broadly within the theoretical predictions in the large and small deformation regimes. In the general intermediate deformation regime, the measurements are well captured by our reduced one-dimensional diffusion model, which does not require the sophisticated and computationally expensive numerical approaches necessary for the original two-dimensional nonlinear coupled transport problem. By adapting modelling techniques from the fluid dynamics of thin porous elastic layers to a polymer swelling problem, our modelling framework extends the range of polymer swelling problems that can be treated with semi-analytical methods. Moreover, our detailed experimental data can serve as a test case for future nonlinear poroelastic frameworks of swelling polymer materials.

Effect of laser cleaning on adhesive properties of carbon fiber composite materials

A pulsed fiber laser was used to conduct laser cleaning experiments on the composite paint layer on the surface of carbon fiber composite materials (carbon fiber-reinforced plastic (CFRP)). The influence of laser energy density and laser travel speed on the cleaning effect was studied. The surface morphology, surface roughness and phase composition of the cleaned sample were analyzed. After bonding, tensile testing was conducted on the bonding part to verify the impact of laser cleaning on the bonding performance. The research results indicate that the cleaning effect gradually improves with the increase of laser energy density or the decrease of travel speed. In this experiment, when the laser energy density is 4.00[Formula: see text]J/cm2 and the travel speed is 6.5[Formula: see text]mm/s, the phase composition of the cleaned substrate surface is only C, without TiO2 and BaSO4. This indicates that the paint layer has been completely removed under this process parameter. By selecting reasonable process parameters, the surface paint layer of CFRP can be effectively removed, and a good surface morphology can be obtained without damage to the carbon fiber. Meanwhile, the mechanical properties after bonding can be improved.

Characterization and Degradation Analysis of Pigments in Paintings by Martiros Sarian: Attenuated Total Reflection Fourier Transform Infrared Spectroscopic Imaging and X-ray Fluorescence Approach

This paper presents a preliminary scientific investigation of pigments used by Martiros Sarian, a prominent Armenian artist known for his vibrant and evocative paintings. The study focuses on five of Sarian’s paintings from different periods of his career, namely, Morning in Stavrino, Arabian Dancer, Caravan, Yerevan Zangu River, and Kirovakan, dated between 1909 and 1948. Non-destructive techniques, including micro-attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopic imaging and X-ray fluorescence (XRF), were employed to characterize the pigments in the samples extracted from these paintings. The results reveal the presence of various pigments, including ultramarine blue, cobalt blue, cobalt cerulean blue, viridian, emerald green, cobalt green, celadonite green, cadmium yellow, chrome yellow, Venetian red, yellow ochre, red ochre, lead white, zinc white, and calcium carbonate. Additionally, metal carboxylates and oxalates, degradation products associated with the paint layers, were observed and discussed. The findings contribute to a better understanding of Sarian’s artistic technique and provide valuable insights for the conservation and restoration of his artworks.

Study of the two-sided icon "Pieta" / "Holy Martyr Barbara" of the 18th century from the Church of John the Baptist in the village of Dorozhiv, Drohobytsky District, Lviv Region, in the context of the separation process of paint layers and transferring them to a new base

The study is devoted to the problems of restoration of the double-sided icon "Pieta" / "Holy Martyr Barbara" using the method of separation and transfer to a new basis of easel painting. Today, the main task of the restorer is the maximum study, research and preservation of the work of art, its history and transformation over time. The article presented the possible reasons for restoration and repainting of artworks of easel painting, as well as the most widely used methods of "preservation", fixing the layers of later repaintings, which lead to their physical loss due to the discovery of an older, original painting layer. Emphasis is placed on the expediency of applying the technique of layering and transfer to a new basis of easel painting, as an alternative in the context of maximum preservation of the entire structure of the artwork, including later historical transformations. The necessary conditions that precede the successful application of the technique of separation and transfer to a new base of artworks of easel painting are specified. There are presented the general conclusions about the state of preservation and the set of conducted physical-chemical and technical-technological studies of the double-sided icon "Pieta" / "Holy Martyr Barbara" of the 18th century from the church of John the Baptist in the village of Dorozhiv, Drohobytskyi district, Lviv region, and a program of restoration activities. Tests on separation of the paint layer of the 19th century from the "Pieta" icon are presented and the obtained results were analyzed, as a result was selected the optimal method of separation of this painting layer as one whole fragment. The entire process of conservation and restoration processes, including the application of appropriate restoration methods, as well as the specifics of the selection and use of restoration materials, is presented and illustrated. The result of this research using the technique of separation is the preserved painting layer of the icon "Pieta" of the 19th century and the painting of the icon of 1726, created by Ivan Seredyskyi, an icon painter of the Rybotytsky Center of Church Art, opened for further study. Attention is drawn to the study of this icon in the context of the work of Rybotyk masters in the monograph of Roksolana Kosiv.

Identification of Chemical and Structural Characteristics of Acrylic Paint Layer Using Terahertz Metasurfaces.

The precise investigation and monitoring of the internal structural change within complex layered systems are crucial, as the emergence of undesirable defects or formation of secondary internal structures significantly exerts a profound influence on the overall properties of the system. We demonstrate an advanced sensing platform utilizing terahertz metasurfaces, allowing chemical detection and precise identification within an acrylic paint layer with a noticeable sensitivity, reaching down to several hundreds of nanometers, in nondestructive and noncontact manners. The identification of solid and mixed paint samples was achieved by analyzing their optical properties, including the refractive index and absorption coefficient. Notably, the presence of internal pore defects within the mixed acrylic paint led to geometric distortions, affecting the state of the overall system. Intriguingly, even in cases where acrylic paint exhibited identical colors perceptible under visible light, distinct discrimination and identification of chemical compositions were successfully proposed.