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Die Klebung von Malschicht und textilem Bildträger. Untersuchung des Eindringverhaltens von Gelatinen sowie Störleim und Methylcellulose bei der Klebung von loser Malschicht auf isolierter und unisolierter Leinwand mittels vorhergehender Fluoreszenzmarkierung – Terminologie, Grundlagenanalyse und Optimierungsansätze
Abstract and Figures
Da neben den Materialeigenschaften von Konsolidierungsmitteln vor allem die präzise Platzierung des Klebstoffs von hoher Bedeutung ist, zeigt die vorliegende Arbeit, wie lose, gerade Bildschollen auf textilem Bildträger mit den gängigen Kon- solidierungsmitteln (Gelatinen, Störleim und Methylcellulose) möglichst nur durch eine Klebschicht ohne Substratpenetration verbunden werden können. Sie möchte vor allem praktizierenden Konservatoren-Restauratoren eine Stütze und Anregung sein.
Als Einstieg in die Thematik dient die Besprechung der Terminologie zur Konsolidierung, die Vorstellung gängiger Vorgehensweisen und die zu beachten- den Parameter bei der Malschichtklebung. Letzterer vorangehende Fluoreszenzmar- kie-rung ermöglichte die Lokalisierung der Konsolidierungsmittel. Dieser Aspekt wird in Kapitel zwei, nebst allen Materialien und Methoden, erläutert.
Das Ergebniskapitel zeigt zunächst das Eindringverhalten von einer bestimm- ten Gelatine bei Veränderung der grundlegenden Parameter, um eine solide Vergleichs- basis hinsichtlich der anderen beiden Konsolidierungsmittel und eine ebensolche Aus- gangslage für das Optimierungsvorhaben zu haben. Anschliessend werden Gelatinen, Störleim und Methylcellulose in einzelnen Parametern erprobt und der Vergleichs-Ge- latine gegenübergestellt. Die letzten drei Unterkapitel (vier bis sechs) thematisieren die Auswirkung von Netzmitteln, aber vor allem widmen sie sich der Vorabsperrung bei unisolierter Leinwand mit aliphatischen Kohlenwasserstoffen, Cyclomethiconen und Cyclododecan, um eine optimale Kleblinie zu erreichen.
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Besides the properties of adhesives, the precise placement of the respective adhesive is enormously important for a successive re-adhesion of loose paint flakes on canvas. This thesis discusses systematic trials of proteinaceous glues (gelatines and sturgeon glue) and methyl cellulose on different absorbent and non-absorbent model systems. The aim is to evaluate the performance of the glues as conservation tools to be used on real artworks.
Chapter one is dedicated to the discussion of terminologies, the presentation of common re-adhesion procedures/approches and the compendium of parameters one should have in mind while re-adhering loose paint flakes.
In chapter two, the main issue is the fluorochromisation of the adhesives in or- der to localise them in the painting. Moreover, materials and methods are introduced. The results are presented in chapter three. First, the penetration of gelatine was analysed by systematically changing basic parameters. These results show the ne- cessity of optimization. The penetration behaviour of other gelatines, sturgeon glue and methyl cellulose were investigated and compared to gelatine type A, 180 Bloom. The last three subchapters deal with the use of surfactants and focus on the significance of temporarily masking the porous substrates with non-polar solvents (aliphatic solvents, cyclomethicones and cyclododecans) in order to prevent the penetration of the adhesive into the material and to thus gain a thin glue line or glue bridges of gelatine.
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... The different mechanisms of film formation are an important determinant of the cohesive stability of the individual materials. However, in the commercial processing of sturgeon glue, the production conditions often are not specified and specifications regarding the origin of the source material vary considerably (Flock 2018, Soppa 2018, Bridarolli et al. 2022. The products may also contain various minor components with potential impact. ...
... The sturgeon glue film was heated only briefly, until it dissolved (40-50 °C). MC was prepared according to the hot/cold method (https://www.youtube.com/watch?v=0XsMNdYF7iY ) and left overnight at 4 °C (Soppa 2018). ...
In this study, films of three common materials used in conservation-gelatin, sturgeon glue, and methylcellulose-were evaluated for dimensional change after 10 humid climatic cycles (53% and 75% relative humidity) under low force (0.1 N). Gelatin and methylcellulose formed stable films that expanded by an equal ratio upon humidifica-tion and contracted after drying. Methylcellulose showed the least dimensional change. The behavior of the two hydrocolloids could be compared to that of elastomers, whereas a very strong plastic deformation of up to 16.5% was observed for sturgeon glue during humidification. The experiment showed that sturgeon glue behaves like a hygro-scopic thermoplastic and that its intermolecular bonds have a potential for rupture. As the cohesive strength of sturgeon glue at increased humidity is thus limited, this material is unlikely to fulfill the basic requirements of an adhesive. An alternative suggested by this research is methylcellulose, which is aging-resistant and exhibits a more stable and uniform behavior.
... Methylcellulose (MC) ethers, specifically the viscosity grades A4M and A4C, have been increasingly used in conservation since the mid-20th century, due to their physicochemical properties, aging stability, and long-term reworkability (Feller andWilt 1990, Steger et al. 2022). The typical applications of MCs are as adhesives, consolidation or retouching media, thickeners, and gelling agents for surface cleaning (Baker 1984, Haller 1995, Hoppmann and Schubert 2005, Horie 2011, Soppa 2018. Recently, MC as adhesive meshes has been researched as well (Konietzny et al. 2018). ...
This paper explores the foaming of methylcellulose (MC) using straightforward foaming and drying methods for different applications in the field of conservation and restoration. The aim was to elaborate a low-tech, inexpensive and reproducible foaming method to achieve dimensionally stable, homogeneous, dried foams. Crucial influencing parameters of the foaming process such as viscosity grade, concentration, water temperature, mixing device, whipping time and drying method were investigated. Dried foams were produced with MC A4C 5-7 wt% and A4M 4-6 wt% and then characterized by comparing them with industrial polyethylene foams, as reference material, with respect to their cell size and compressive strength. The tested samples consisted of heterogenous cells between 0.3 and 2.3 mm in diameter, and the hardness was 1.2-15.1 N/cm 2. Possible areas of application of dried MC foam in the field of conservation-restoration, e.g. as a filling material, are explored within a case study.
This article addresses the topic of liquid methylcellulose (MC) foam and its use in conservation. The focus of the research is the use of MC foam to underfill rigid, fragile, and lifted paint layers or voids on artworks. The MC foam is produced using the double-syringe technique, which results in the formation of connections that are sufficiently strong to reinforce fragile paint layers. The use of foam minimizes the input of material compared to other applications. A detailed recipe for making MC foam with the double-syringe technique is presented. The foam form of the long-chain cellulose ether Methocel© A4M dissolved in water was evaluated. In preliminary tests, samples were used to determine how homogeneously the MC foam dried when placed between two highly absorbent surfaces. The effects of adding fiber and drying with heat were investigated as well. Foam characterization was performed by examining the pore size and plateau borders of the foams in cross-section with digital microscopy (Keyence VHX1000) and electron microscopy SEM–SE. The foam’s drying behavior and percentage of shrinkage were evaluated with a precision balance (Sartorius Practum 224-1S). Tests of compressive strength and adhesive strength were performed on the Zwick 1120/TNS1 (software testXpert, testing speed 1mm/min). A work on paper by Silvia Buol, Baleines II (2018; Kunstmuseum Basel) served as a case study for the liquid foam application.
This case study presents a novel approach to gluing a poorly fitting open joint on a polychromed 16th century lime- wood relief, relying on digital 3D technology. Photogrammetrically generated digital 3D models of the two gluing surfaces allowed in a first step to analyze the conditions in the virtually recreated joint and then to produce a CNC-routed wooden infill to bridge the large gap between the two fragments.The precise infill allowed for an adhesive mixture consisting of a short-chained cellulose-ether and microfibrillated cellulose.The formulation was successfully tested before on a series of samples produced with a simple “open- source” press system.
Adhesive meshes are micro-structured and honeycomb-shaped, flexible adhesive nets. They can be produced from a variety of adhesives such as water-soluble methylcelluloses or sturgeon glue. These two have proofed long-term stability for several decades now and have found wide application in the field of conservation. If a painting allows for temporary use of moisture, adhesive meshes provide an interesting alternative to common adhesives, such as acrylic dispersions and hot-melt adhesives, as their application does require neither heat nor organic solvents. The dry adhesive meshes are positioned in place and activated using a controlled supply of water. Depending on the accessibility of the bonding area, water can be sprayed or applied by a suitable carrier material like capillary non-wovens. After activation, the parts are joined under light pressure until dry. This technique provides an exceptionally uniform distribution of the adhesive throughout the bonding surface, a permeable and reversible bonding, and as such assuring a minimally invasive and highly controllable treatment. So far, several case studies underpin the practical applicability, comprising strip lining, full linings, the application of small patches at the tacking margin or the re-attachment of failing historic linings along the edges.
Originating from a diploma project at the Dresden University of Fine Arts (HfBK Dresden), Germany, adhesive meshes were further investigated within a research project at the Bern University of Applied Sciences in cooperation with APM Technica AG, both Switzerland, and the HfBK Dresden. The outcome was an improved production process, commercial availability of adhesive meshes, and widening the product range by investigating basic adhesive properties of methylcellulose meshes. This current contribution explored adhesive meshes made of Methocel™ A4C (400 mPa·s) and Methocel™ A15LV (15 mPa·s) with respect to material and adhesive properties in comparison to the physical behavior of BEVA® 371 films. Commercial adhesive meshes, mass-produced by APM Technica, were compared to self-made adhesive meshes, manufactured using a laser-cut silicone mold. Canvas specimens were bonded with adhesive meshes, activated using a standardized spraying technique for laboratory tests. Bonding properties were determined by lap shear tests according to DIN EN 1465 that was adapted to canvas specimens. The results show that adhesive strength varies depending on the amount of activation water and the viscosity of the methylcellulose. Commercial and self-made adhesive meshes show similar tendencies despite the different weight per unit area (grammage). Both manufacturing modalities resulted in similar trends in bond strength. Due to the overall lower grammage, self-made Methocel™ A4C adhesive meshes require smaller amounts of water for activation, whereas APMˈs adhesive meshes are capable of higher maximum adhesive bond strengths when activated sufficiently. In general, the bond strength of adhesive meshes made from medium-viscosity Methocel™ A4C increases with the amount of activation water and can be adjusted over a wide range from slight to very strong adhesion. A moderate amount of activation water of ≥200 g/m² results in high to very high bond strengths, which are equal to and even exceed those of BEVA® 371 films. Adhesive meshes made from the low-viscosity Methocel™ A15LV achieve lower bond strengths, yet require smaller amounts of water ≤200 g/m² for activation. A higher water input leads to dissolution of the mesh, to a deeper penetration of the glue into the canvas and finally to a decrease in bond strength. In conclusion, adhesive meshes made from Methocel™ A4C meet the requirements when canvas bonding needs to withstand high tensile stress, e.g. with strip lining. Methocel™ A15LV meshes are, on the other hand, particularly suited to attach smaller patches exposed to low or moderate stress. They proved suitable for poorly accessible bonding surfaces and water-sensitive materials where only a minimum of humidity is acceptable.
Wetting of real engineering surfaces occurs in many industrial applications (liquid coating, lubrication, printing, painting, …). Forced and natural wetting can be beneficial in many cases, providing lubrication and therefore reducing friction and wear. However the wettability of surfaces can be strongly affected by surface roughness. This influence can be very significant for static and dynamic wetting [1]. In this paper authors experimentally investigate the roughness influence on contact angle measurements and propose a simple model combining Wenzel and Cassie–Baxter theories with simple 2D roughness profile analysis. The modelling approach is applied to real homogeneous anisotropic surfaces, manufactured on a wide range of engineering materials including aluminium alloy, iron alloy, copper, ceramic, plastic (poly-methylmethacrylate: PMMA) and titanium alloy.
Protein-based adhesives – a well known material? The change in mechanical properties during ageing (humidity cycles) was investigated. Gelatin films are very moisture-sensitive systems that react with internal tensions in function to varying humidity levels. The inner molecular structure of gelatin is discussed with relation to its production, its mechanisms of water absorption, and its reaction time to determine the shrinkage behavior as a degradation factor (mechanical tension). Under 65% RH, the gelatin film exerts mechanical tension. Above this limit, the system starts to change its characteristics: besides contraction, relaxation was also observed in characteristic levels of water activity of the material.
„How does it work?“ This is the central question of the following educational article on the effect of solvents and the solubility of materials. In order to understand dissolution processes, it is essential to know the fundamentals of solvent properties and the materials to be dissolved. These build the theoretical framework to set up conceptual strategies in restoration practice. The thermodynamics are the basis for the presented concept. Part I highlights relevant aspects of the dimension“ enthalpy”, whereas Part II discusses the dominant dimensions of “entropy”. In principle, we need to consider three dimensions of energy, which define the solubility of a material: the “cohesive energy” of the solid to be dissolved, the “solvation energy”, that is the energy of interaction between solvent and solute, as well as the “cavitation energy” of the liquid. The cohesion of the solid therein is the only dimension, which cannot be influenced under normal working conditions. Cohesion is defined by the intermolecular interaction, the density of entanglement of the macromolecules, the degree of crystallinity and the cross-linking situation. The cohesion controls whether a material is soluble at a specific temperature. Interaction between polymer molecules and the solvent influences the solvation and is determined by the “affinity” of the solute to the solvent. In the practical context this means that the interaction must be sufficiently strong for the solute molecule to be held in the solvent. This, in turn, depends on the functional groups present and their accessibility within the compound structure. Solvation defines the range of polarity wherein a specific material can be dissolved. A parametrisation system is introduced as a working tool to visualise the correlation of these dimensions. Low molecular materials are often soluble over a broad range of the polarity spectrum, whereas high molecular compounds require well-defined interaction conditions. The most decisive dimension, however, is the cavitation energy, i.e. the cohesion energy of the liquid. This determines the entropy of the dissolution process and as such is the driving force in the process of mixing. The cavitation energy is the key dimension to describe the rate of dissolution. As a general rule we can derive that low molecular molecules have a higher tendency to mix than high molecular ones, and apolar molecules dissolve faster than polar ones. The rate of dissolution can, in principle, be controlled by manipulation of the vapour pressure of the solvent. An additional factor influencing the dissolution behaviour is the morphology of a material. General trends are discussed based on the dissolution behaviour of a broad range of materials tested. This is achieved either by selection of a suitable solvent within defined groups of solvents, or by systematic mixing of solvents. Further aspects such as “leaching” upon short-term action of solvents on oil paint will be illuminated. Part III finally delivers the tools and strategy on how to perform solubility tests on micro-samples in practice and how to derive a sound choice for a suitable solvent, based on the presented scheme.
„How does it work?“ This is the central question of the following educational article on the effect of solvents and the solubility of materials. In order to understand dissolution processes, it is essential to know the fundamentals of solvent properties and the materials to be dissolved. These build the theoretical framework to set up conceptual strategies in restoration practice. The thermodynamics are the basis for the presented concept. Part I highlights relevant aspects of the dimension“ enthalpy”, whereas Part II discusses the dominant dimensions of “entropy”. In principle, we need to consider three dimensions of energy, which define the solubility of a material: the “cohesive energy” of the solid to be dissolved, the “solvation energy”, that is the energy of interaction between solvent and solute, as well as the “cavitation energy” of the liquid. The cohesion of the solid therein is the only dimension, which cannot be influenced under normal working conditions. Cohesion is defined by the intermolecular interaction, the density of entanglement of the macromolecules, the degree of crystallinity and the cross-linking situation. The cohesion controls whether a material is soluble at a specific temperature. Interaction between polymer molecules and the solvent influences the solvation and is determined by the “affinity” of the solute to the solvent. In the practical context this means that the interaction must be sufficiently strong for the solute molecule to be held in the solvent. This, in turn, depends on the functional groups present and their accessibility within the compound structure. Solvation defines the range of polarity wherein a specific material can be dissolved. A parametrisation system is introduced as a working tool to visualise the correlation of these dimensions. Low molecular materials are often soluble over a broad range of the polarity spectrum, whereas high molecular compounds require well-defined interaction conditions. The most decisive dimension, however, is the cavitation energy, i.e. the cohesion energy of the liquid. This determines the entropy of the dissolution process and as such is the driving force in the process of mixing. The cavitation energy is the key dimension to describe the rate of dissolution. As a general rule we can derive that low molecular molecules have a higher tendency to mix than high molecular ones, and apolar molecules dissolve faster than polar ones. The rate of dissolution can, in principle, be controlled by manipulation of the vapour pressure of the solvent. An additional factor influencing the dissolution behaviour is the morphology of a material. General trends are discussed based on the dissolution behaviour of a broad range of materials tested. This is achieved either by selection of a suitable solvent within defined groups of solvents, or by systematic mixing of solvents. Further aspects such as “leaching” upon short-term action of solvents on oil paint will be illuminated. Part III finally delivers the tools and strategy on how to perform solubility tests on micro-samples in practice and how to derive a sound choice for a suitable solvent, based on the presented scheme.
A new technique using a microstructured system with sturgeon glue was developed and applied to stabilize a detached historic lining of a canvas painting. The main goals are to minimize introduction of adhesives, to keep characteristics of the textile intact, and to guarantee reversibility of the treatment. The adhesive mesh bonding was tested for its adhesive stregth, homogeneity, penetration potential, reversibility, and fracture pattern.
Analysis of tempera paint binding media presents various challenges. Firstly, the binding medium of a particular paint can consist of many components that may be difficult
to identify simultaneously within a tiny, single sample. Secondly, many tempera paintings created around 1900 consist of complex layered structures; heterogeneous layers of paint were applied one on top of another, sometimes superimposed with unpigmented intermediate layers whose presence can be difficult to recognise, especially when they are thin. Thirdly, because many tempera paints are somewhat lean, the binders present in the
uppermost layers can easily penetrate underlying stratigraphy, making a distinction between actual binding medium and binder contamination from adjacent layers very difficult, if not impossible.
This study focusses on the investigation of tempera easel painting techniques in Munich between 1850 and 1914. During this period, tempera painting evolved to a trend that was joined by various artists of different art movements. This investigation complements previous studies on this topic, which mainly relied on the analysis of written sources, with an interdisciplinary approach that combines art technological examinations and a comprehensive evaluation of the written sources.
The main focus is to investigate the individual painting techniques of four important protagonists of the Munich art scene at that time: Arnold Böcklin (1827–1901), Franz von Stuck (1863–1928), Franz von Lenbach (1836–1904) and Wassily Kandinsky (1866–1944). The study outlines how they learned to paint in tempera, which models they had and how they passed on their practical knowledge. Furthermore, it shows up the wide range of painting materials and the various possibilities of their application: The artists could choose between various self-made tempera paints and commercially available tempera paint tubes, which they applied either alla prima or in layers. This results in a wide range of different paint appearances, ranging from a tempera-like appearance in the classical sense up to a wet-on-wet modelled alla prima painting, which is conventionally associated with the visual appearance of oil painting. Consequently, tempera painting helped them to extend their individual means of expression compared to traditional oil painting, which is – in addition to an improved durability and a more rational way of painting – the main reason for their fascination of the tempera painting technique.