New Applications in the Use of Cellulose Pulp for the Integration of Wooden Supports

Wooden panel paintings are among the most important historical and artistic artworks from the Middle Ages and the Renaissance period. Currently, they represent a challenge for conservators and scientists who face complex issues related to their conservation. Panel paintings can be considered multilayer objects, that for brevity can be considered to consist of a wooden support and various paint layers. The wooden support is known to be hygroscopic and is continuously seeking hygroscopic equilibrium with the humidity of the environment, thus it tends to deform. Based on various hygroscopic tests carried out on 6 real panel paintings chosen by expert restorers to represent different periods and construction techniques, this paper describes the deformation tendencies of the selected panel paintings. Among possible variables, three most important variables were identified: (a) tree ring orientation of the wooden support, (b) stiffness and (c) emissivity of the paint layers. The internal equilibrium of the forces, governed by the moisture gradients across the thickness of the wood, changes drastically according to the varying characterisation of these factors. To observe their individual contributions, the 6 panel paintings underwent various humidity cycles, were completely free to deform and were always in complete safety. To characterise the stiffness and emissivity of the paint layers, the 6 panel paintings underwent a few humidity cycles with the front face totally waterproofed; thus, the moisture exchange was forced from the back only, and one of the three variables was eliminated. A complex system emerges where the tree ring orientation of the wooden support, the stiffness and emissivity of the paint layers are strongly coupled and determine the deformation modes of the panel paintings. A numerical analysis was conducted to classify the various general deformation modes of panel paintings and the specific classification of the 6 real panel paintings analysed experimentally. The complexity of the interaction of the variables studied suggests that experimental procedures must be conducted in preparation for numerical analyses of real panel paintings.

The interest in the mechanical behaviour of wood is a very important task due to the increasing role played by wood structures in modern architecture as well as its applicability in restoration of ancient buildings. The behaviour of wooden surfaces experiencing variable humidity conditions is of great importance both with concern to performances of wooden building’s structures and to ensure correct restoration and conservation of art works like wooden sculptures and panel paintings [1]. In literature there are only a few studies dealing with the influence of moisture on the physical properties of wood [1,2]. The characterization of wooden behaviour related to changes in the humidity level could make easier restoration and preservation of wooden artefacts. In the last years, the increasing development of technology allowed the application of non contact wholefield measurement techniques. These techniques could play a fundamental role in the analysis of the mechanical behaviour of materials such as plastic and wood. Among these techniques: Digital Image Correlation, Structured Light, Electronic Speckle Pattern Interferometry (ESPI) [3]. Recently some real-time 3D wood panel surface measurement using laser triangulation [4] and light shadow scanning [5] have been proposed.

Purpose Artworks made of hygroscopic materials, like wooden panel paintings, are susceptible to environmental conditions. Traditional panel paintings typically consist of a wooden panel coated with layers of gesso, paint and varnish. Due to environmental fluctuations, the gesso layer and the wood panel may respond differently to moisture changes, triggering potential fractures. The investigation of such phenomena is of high interest, but it is still scarcely studied by engineers. Design/methodology/approach The proposed study aimed to create a simplified 3D finite element model for paintings to identify environmental conditions that could exceed critical strain levels. A penny-shaped crack within the gesso layer was modelled and, after applying a given deformation, the strain energy density failure criterion was used to assess if the crack was in a critical state. Findings Various combinations of geometric parameters of the model were explored, and to save computational time and cost, machine learning algorithms (namely extreme gradient boosting machines and Gaussian process regression algorithms) were introduced. The analyses were carried out on different panel paintings 3D models obtained by varying the wooden species and the boundary conditions, for exploring a wide number of combinations. Originality/value Moreover, the integration of machine learning can potentially reduce the reliance on numerical simulations and offer new insights into the conservation of artworks, a field in which such tools are still scarcely exploited.

Continuous monitoring of wooden works of art using fiber Bragg grating sensors

A collaboration aiming to improve knowledge and procedures for conservation of Panel Paintings has been in force since several years between OPD (Opificio delle Pietre Dure, Florence) and the Research Group on Wood Technology of DAGRI (University of Florence). In such framework a research is here presented, which for the first time has led to dimensioning rationally (i.e. by means of objective criteria based on Conservation, on Engineering and on Wood Science principles) the stiffness of the crossbeams of an original Panel Painting. Crossbeams typically have a double function: a) to control the deformation of the panel painting when it undergoes climate changes and b) to stiffen the panel painting for handling purposes. If too stiff or too yielding, crossbeams might damage the wooden support or the paint layers; until today the choice of their stiffness was entrusted to the expert but subjective judgment of the Restorers alone, who therefore have been calling for a confrontation with Wood and Engineering Scientists in order to develop more objective criteria. To satisfy this request the research here mentioned has been carried out, in close collaboration between the Restorers of OPD and the Wood Scientists of DAGRI, to develop a specific protocol allowing for the rational dimensioning of the stiffness of crossbeams. This protocol is based on an engineering modular approach, and for the first time it has been applied on an original artwork, the Adorazione del bambino e committente attributed to Cesare da Sesto (1514-1520). One of the modules of such protocol is to assess the stiffness of both the crossbeams and the wooden support and, in such framework, this paper presents the non-invasive mechanical tests that were designed and implemented to check in-situ various mechanical parameters (including the axial holding capacity) of the original nail connections between the crossbeams and the wooden support. Such knowledge might in general be helpful especially during the diagnostic phase, to understand the internal forces still acting into the wood structure, and possibly their influences on the degradation of the paint layers in relation to the behaviour of the wooden support.

In this article, a multidisciplinary methodological approach for studying a wooden panel painting is applied. The theoretical framework, within which this research has arisen, is the application of state-of-the-art non-destructive techniques for addressing issues concerning the constituting parts and composing materials of the artwork. Hereby, a post-Byzantine icon was studied, which was dated back to 1836. It is a painting executed on a wooden panel, with a decorated wooden frame attached. The artifact was thoroughly investigated through the application of infrared thermography (IRT), multispectral imaging (MSI), and macroscopic X-ray fluorescence spectrometry (MA-XRF). These analyses provided crucial information about the verso of the painting (i.e., the wooden panel and the frame) and allowed for the revelation of important details of the recto of the painting, which were not visible due to the presence of an old, decayed varnish. Additionally, through the detailed mapping of the distribution of various chemical elements on the recto of the painting and the frame, it was possible to identify the materials used and techniques employed. It is therefore shown that, when combined, the non-destructive methodologies in consideration can provide adequate information referring to the materiality and state of preservation of panel paintings, permitting the conservator to proceed to a tailored conservation treatment.

Wooden Panel Paintings (WPPs) stand as invaluable cultural artefacts from the past. These works present an intriguing challenge in understanding their complex mechanical behaviour and ensuring their long-term preservation. The present study assumes as founding paradigm the unicity of each WPP, in terms of its material composition, historical background, physical dimensions, and the specific environmental conditions it has been subjected to over time, and their complex behaviour, which requires the knowledge of both mechanical and materials specificity. These characteristics need to be considered, and studied in-depth for each individual WPP, particularly if the aim is to develop a comprehensive understanding of its individual mechanical behaviour. The study provides new computational models calibrated to reproduce the physical and mechanical behaviour of artworks and acting as their 'digital twins'. The models developed contribute significantly to the understanding of the mechanics of these artworks, including the impact of environmental thermo-hygrometric fluctuations and the role of structural elements such as crossbeams. The results, corroborated by experimental analyses, indicate that environmental variations, both short and long term, exert specific and quantifiable effects on the WPPs, and that the presence of crossbeams significantly influences the distribution of stresses within the panel, particularly affecting the pictorial layers that are often the most susceptible to damage. In this context the generated digital twins serve as an invaluable tool, offering the potential to simulate various risk scenarios or to evaluate the effectiveness of engineered conservation interventions on the WPPs.

Wooden Panel Paintings (WPP) are among the most significant historical and artistic artifacts from the Middle Ages and Renaissance and pose a challenge to conservators and scientists in both their comprehension and conservation. From a structural point of view, they can be considered as multi-layered objects, consisting of a wooden support and several pictorial layers. The wooden support, hygroscopic in nature, constantly seeks equilibrium with the humidity of the environment, and consequently deforms. Based on a series of hygroscopic tests carried out on six original WPPs, the present work aims to model their deformation tendencies induced by moisture changes and to characterise them by means of an inverse identification process. The sensitivity analysis of this study provided valuable insights into the complexity of the phenomenon of WPP deformation: even small variations in input variables (board anatomy, stiffness and emissivity of pictorial layers) led to significant changes in the deformation trend over time, highlighting the high variability of the physical problem under investigation. Sobol's analysis variance confirmed this complexity, demonstrating the different levels of influence of input variables and the existence of interactions between them. Overall, the results of this analysis highlighted the need to carefully evaluate the interactions and uncertainties in input variables to fully understand the complexity of the system. The iterative optimization process led to numerical results tending to agree with experimental data, with most results showing a very high correlation. This suggests that the chosen variables and modelling assumptions sufficiently described the physical system and that numerical models can be accurately calibrated. The proposed concept of 'learning from objects', by conducting experimental investigations specifically dedicated to understanding the deformation tendencies of the artwork, is essential. In this approach, numerical analysis is used in conjunction with experiments to gain a deeper understanding of the artwork, characterise it and extract valuable information.

Ancient wooden panel paintings are an essential part of our cultural heritage. Wood as artworks support has always been very popular and painted panels are largely diffuse in many churches and museums. However, depending on conservation conditions, the wooden panels shape may vary and, if not properly controlled, may lead to some sever damage to the artworks. This paper presents the results of a study on the measurement of paintings surface deformation carried out using two different three-dimensional acquisition devices both making use of structured light. The main goal was to highlight and measure the reliability of such 3D measuring techniques to evaluate deviations from planarity due to the curving and warping of the wood and to document spatial deformation suffered by the painting and monitoring its conservation status.

Thermography is a technique whereby the construction or condition of objects is studied by means of precisely measuring temperature variations over the surfaces of such objects. Voids within solid structures tend to cause cold or hot spots on the surfaces of these structures as the whole object is heated or cooled slightly. Industrially, thermography is used to detect voids in cast and laminated structures. By studying areas of known voids in test panels, the described research indicated that voids as small as 1/8 in diameter beneath the gessoed surfaces of wooden panels could be resolved with a raster scanning radiometer, the principal instrument used for thermo- graphic studies. Smaller voids were discernible when they were grouped together. Only voids im- mediately beneath the gessoed surfaces of the test panels were detectible. Additional tests indi- cated that areas of simulated cleavage between the wood support and the gesso layers on the test panels could be detected thermographically. Thermography is the technique whereby the structure or condition of objects is studied by means of precisely measuring temperature variations over the surfaces of such objects. Research was undertaken to determine whether thermographic techniques could be ap- plied to the field of art conservation to detect subsurface voids within painted wooden panels. It must be stressed, however, that this research was carried out as a feasibility study with no attempt being made to establish or refine a technique that could be im- mediately applied to the examination of works of art. Blind cleavage and worm tunneling are two manifestations of the deterioration of panel paintings that can be difficult to detect. The term cleavage refers most often to a loss of bond between two paint layers, between a paint layer and the ground layer, or between the ground layer and its support. Blind cleavage is simply a form of cleavage that cannot be de- tected visually. Worm tunneling is the condition affecting panel paintings wherein insects

PurposeThis paper aims to provide a deeper understanding of the painting techniques, materials used and deterioration phenomena in a thin panel painting. As well as, straightening buckling in a thin panel painting and reinforcement have been used by an auxiliary support system.Design/methodology/approachThis requires using several scientific and analytical techniques to provide a deeper understanding of the painting techniques, materials used, deterioration phenomena and a greater awareness of how well treatment the panel painting is. Visual observation and multispectral imaging (Visible Ultraviolet-induced luminescence, as well as Ultraviolet reflected and Infrared [IR]), optical Microscopy (OM), handheld X-ray fluorescence spectroscopy (XRF), X-ray diffraction, Fourier transform IR spectroscopy (FTIR) and gas chromatography were used in this case study.FindingsThe analytical study of a thin panel with different methods allowed defining that the thin panel painting consists of plywood panel, ground layer (white lead and animal glue) and painted layer (lead red, cobaltic black, chrome yellow, Venetian red, iron black and white lead and poppy oil). Also, these determined that a convex buckling was the main form of deterioration. The structure treatment was executed by using a wet compress to straighten the thin panel painting and followed by fixing a new special design of the second auxiliary support system on the back of the thin panel painting.Originality/valueThe importance of analytical study to determine the painting techniques, materials used, deterioration phenomena and how well treatment the panel painting is. As well as, using a wet compress to straightening of warping or buckling wooden panel painting. Also, the Plexiglas second auxiliary support system could use to reinforcement the wooden panel and control the wooden panel movements.

In this paper, a method for the study of wooden panel paintings using air-coupled acoustical imaging is presented. In order to evaluate the advantages of the technique, several samples were made to mimic panel paintings along with their typical defects. These specimens were tested by means of both single-sided and through-transmission techniques using planar transducers. Image data were processed by means of a two-dimensional (2-D)-fast Fourier transform-based algorithm to increase the S/N ratio and 2-D representations (C-scans) were generated. The simulated defects were imaged using both configurations. Investigations were undertaken on four antique paintings from a private collection. The results presented and discussed in this investigation confirm both the robustness and the effectiveness of the technique in detecting defects such as delaminations and cracks in wooden panel paintings.

The goal of this research is to create biodegradable plastics made from Paragis grass (Eleusine indica) cellulose-pulp that can be used as alternatives to traditional plastics. The bioplastics were made by combining cellulose pulp from paragis grass leaves, sorbitol, acetic acid, and corn starch, with a constant amount of 8g corn starch and varying amounts of cellulose pulp (20g, 30g, and 40g), as well as 10ml sorbitol and 3 ml acetic acid. Collection and processing of paragis grass, cellulose pulp manufacturing, and bioplastic film manufacture were some of the methods used. Tensile strength, biodegradability, water absorption, and water solubility tests are used to characterize bioplastic. The mechanical properties testing shown that bioplastic produced with variation of corn starch to paragis grass cellulose pulp ratio had a tensile strength of 0.549 MPa, 0.878 MPa and 1.03 MPa; elongation at break (%) of 7.33%, 6.97% and 6.54%; biodegradability (weight loss) of 91.65%; 90.05%; and 69.46%; water absorption (weight gain) of 91.80%, 83.06% and 53.74%; and water solubility (weight loss) of 86.96%, 66.46% and54.91% respectively. The study found that Treatment 3 (40g paragis grass) has higher tensile strength (1.03 MPa) and tear strength, ability to degrade in four weeks, low water absorption (53.74%), and water solubility (54.91%).The result showed that cellulose-pulp from Paragis grass leaves could be used to make bioplastic. This research would aid in the reduction of plastic waste that pollutes the Earth’s soil, air, and water, as well as the mitigation of its consequences. It can also help reduce environmental pollution by using biodegradable plastic.

In this work, the use of different cellulosic pulp samples to prepare new formulations potentially applicable as biodegradable lubricating greases is explored. Cellulosic pulps from different raw materials and submitted to different pulping process and/or several acidic treatments were characterized and used as biothickener agents to formulate gel-like dispersions. Cellulose pulp samples mainly differed in polymerization degree (160−893 cm3/g) and lignin (0.3−27.1% w/w) and α-cellulose (46.0−85.1% w/w) contents. Rheological measurements and some standard mechanical tests usually performed with lubricants were carried out. The rheological response of cellulosic pulp-based gel-like dispersions is mainly a consequence of the balance between the cellulose polymerization degree and lignin and α-cellulose contents, independently on the origin of cellulose samples and pulping treatment. An empirical correlation between a power function of these variables and the plateau modulus has been proposed to predict the rheological behavior of resulting formulations. However, cellulosic pulp-based dispersions studied generally present either poor mechanical stability or low consistency indexes than expected for lubricating greases.

This study focuses on the magnificent decoration of a painted and gilded wooden panel with signs of fungal biodeterioration caused by Aspergillus species in the Mausoleum of Sultan al-Ashraf Qaytbay, Cairo, Egypt. Numerous spectroscopic analyses and investigation techniques, including Scanning Electron Microscope Equipped with Energy Dispersive X-ray analysis (SEM–EDX), Fourier Transform Infrared analysis (FTIR), and X-Ray Diffraction (XRD) have been used to study the materials that comprise this painted and gilded wooden panel composition. Aspergillus niger, A. flavus, and A. terreus were recognized as isolated fungi, and their accession numbers are OQ820164, OQ820163, and OQ820160, respectively. The findings showed that the wooden support is of pinewood (Pinus halepensis), the white priming layer on top of the wooden support was identified as gypsum, the blue paint layer has been proposed to be Azurite, Au (gold) was the primary composition of the gilding layer, while Pb (lead) was detected in some spots, suggesting the use an alloy of gold with lead, and finally, animal glue was the bonding medium. Based on these findings, mimic samples with identical substrates and structural components have been designed, and the biodeterioration signs by the growing of the three Aspergillus species—A. niger, A. flavus and A. terreus were evaluated via SEM and color change. However, A. niger was discovered with density growth on surfaces of pinewood, gypsum, and Azurite and with less growth on the gilding layer after 6-month incubation. This contrasts with A. terreus and A. flavus, which had greater density growth on Azurite and stucco than on pinewood and less growth on the gilding layer. The used analytical methods with detailed analyses revealed the novelty and significant future aspects of the conservation of the painted and gilded wooden panel. Particularly given that this location is used for prayer and is crowded with people five times a day, which increases the accumulation of fungi and negatively affects both the historic Mosque and the worshippers' health.