Wooden Panel Paintings (WPP) are among the most significant historical and artistic artifacts fro... more 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.
Wooden panel paintings are among the most important historical and artistic artworks from the Mid... more 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 ...
Wooden Panel Paintings (WPPs) stand as invaluable cultural artefacts from the past. These works p... more 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.
IOP Conference Series: Materials Science and Engineering, 2020
A collaboration aiming to improve knowledge and procedures for conservation of
Panel Paintings h... more 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.
This paper describes the most recent results of some experimental
tests carried out on wooden pa... more This paper describes the most recent results of some experimental
tests carried out on wooden panel paintings,
in the context of a close collaboration between the
Opificio delle Pietre Dure and DAGRI (University of
Florence). Starting from the assumption that each panel
painting is a unique entity regarding its composition,
conservation state and history, our approach is now
based on the study of the individual object rather than a
deterministic model. The research considers three main
variables as the origin of the deformation in panel paintings
under climatic variations: the tree ring orientation
of the planks, the emissivity of the paint layer and the
stiffness of the ground layers. The research aim was to
establish a method to determine the deformation behaviour
of panel paintings and the containing effect of the
restraining system, in order to dimension the restraining
system itself on engineering basis. Thus, six Florentine
panel paintings dating from the 14th to the 16th century
were chosen as examples of constituent materials,
construction peculiarities and conservation conditions.
To characterize the panel paintings, each one safely
underwent controlled hygroscopic variations and their
deformation behaviour was measured. The main results
are a) the panel paintings show two different deformation
behaviours, the Flying Wood and the non-Flying
Wood behaviour; b) the paint layers and varnish show
a specific emissivity depending on their specific characteristics;
and c) the stiffness of the ground layers strongly
contributes to the deformation behaviour of their specific
panel painting. For the first time, this research has determined
the hygro-mechanical characteristics of panel
paintings by means of experimental tests and numerical
modelling. Due to the large technical differences of
panel paintings, we consider this approach the only possible
one for dimensioning the restraining system on a
scientific basis that should be necessarily adjusted to the
conservation needs of the individual objects.
The Future of Heritage Science and Technologies, 2023
Most panel paintings feature mechanical systems, typically made of
AQ1 crossbeams, designed to co... more Most panel paintings feature mechanical systems, typically made of AQ1 crossbeams, designed to control the distortion of the panel.When the crossbeams are too stiff or too yielding in relation to the distortion tendency of the panel, significant damage to the artworkmay occur. The evaluation of the factors causing thedamage necessarily relies on the restorer’s experience and wisdom; however, in the framework of a long-standing cooperation between Opificio delle Pietre Dure (Florence) and the Research Group on Wood Technology of DAGRI Department (University of Florence), an innovative method has been developed to provide additional objective criteria for dimensioning the crossbeams system. A specific protocol was developed, based on an engineering approach and consisting of the following five “modules”: a) a Restoration Plan, developed by restorers and conservators, b) appropriate mechanical tests to evaluate the stiffness of the painted panel alone and of the crossbeams alone, c) hygroscopic tests to evaluate the hygro-mechanical behaviour of the painted panel alone, d) appropriate numerical modelling for dimensioning the panel-crossbeams system, and e) numerical and/or experimental verification of the dimensioning. This paper describes such protocol and its first implementation on an original panel painting, the Adorazione del Bambino e Committente (in brief called Nativity) attributed to Cesare da Sesto (1514–1515).
Diagnosing wood artworks surface through state-of-the-art high-resolution optical 3D imaging tech... more Diagnosing wood artworks surface through state-of-the-art high-resolution optical 3D imaging techniques " Uwe Noldt Monitoring wood-destroying insects in wooden cultural heritage "
Strain gauges were attached to both faces of 10 mm thick Poplar wood panels before applying a tra... more Strain gauges were attached to both faces of 10 mm thick Poplar wood panels before applying a traditional gesso-based ground layer and varnish on only one face. The application and setting of the ground layer left high strains on both faces of the wood panels. Later measurements, followed by geometrical calculations, showed that for step-humidity changes the strains in the outer surface of the gesso ground layers were small. These results were followed by numerical calculations to indicate the behaviour of thicker panels and with different stiffnesses. These indicated that the strain levels in the ground layer are strongly dependent on the ratio of the thicknesses of the ground layer to the wood, and also weakly dependent on their stiffness ratios. Further calculations showed that the prevention of cupping by mechanical restraint can increase by many times the strains in the ground layer surface, but this also is dependent on the panel thickness. In this paper, the authors have tried to provide some background information about the strains that can result either from moisture changes or from external restraints; to help the conservators make a decision in any specific case.
Lignocellulosic substrates such as wood have been found to have a marked modifying influence on b... more Lignocellulosic substrates such as wood have been found to have a marked modifying influence on both lower-temperature and higher-temperature zones of TTT and CHT diagrams during hardening of formaldehyde-based polycondensates. While the modifying influence of the substrate has been described, the modifying influence of some of the most important manufacturing parameters of the resins on the CHT diagram, not having been previously investigated, are explored here and clear trends are shown. In the case of melamine-urea-formaldehyde (MUF) resins for wood adhesives, the molar ratio (MϩU):F appear to be the dominant parameter influencing the relative position of gel and vitrification curves in relation to each other. The ratio of melamine to urea does not appear to have any effect on the relative position of the curve, lacking any clear trend, at least at the higher (MϩU) molar ratio of 1:1.9 used for this series of resins. In the case presented for the first time, the influence of resin manufacturing parameters on CHT curing diagrams was studied in combination with the modifications introduced by the substrate.
Wooden Panel Paintings (WPP) are among the most significant historical and artistic artifacts fro... more 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.
Wooden panel paintings are among the most important historical and artistic artworks from the Mid... more 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 ...
Wooden Panel Paintings (WPPs) stand as invaluable cultural artefacts from the past. These works p... more 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.
IOP Conference Series: Materials Science and Engineering, 2020
A collaboration aiming to improve knowledge and procedures for conservation of
Panel Paintings h... more 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.
This paper describes the most recent results of some experimental
tests carried out on wooden pa... more This paper describes the most recent results of some experimental
tests carried out on wooden panel paintings,
in the context of a close collaboration between the
Opificio delle Pietre Dure and DAGRI (University of
Florence). Starting from the assumption that each panel
painting is a unique entity regarding its composition,
conservation state and history, our approach is now
based on the study of the individual object rather than a
deterministic model. The research considers three main
variables as the origin of the deformation in panel paintings
under climatic variations: the tree ring orientation
of the planks, the emissivity of the paint layer and the
stiffness of the ground layers. The research aim was to
establish a method to determine the deformation behaviour
of panel paintings and the containing effect of the
restraining system, in order to dimension the restraining
system itself on engineering basis. Thus, six Florentine
panel paintings dating from the 14th to the 16th century
were chosen as examples of constituent materials,
construction peculiarities and conservation conditions.
To characterize the panel paintings, each one safely
underwent controlled hygroscopic variations and their
deformation behaviour was measured. The main results
are a) the panel paintings show two different deformation
behaviours, the Flying Wood and the non-Flying
Wood behaviour; b) the paint layers and varnish show
a specific emissivity depending on their specific characteristics;
and c) the stiffness of the ground layers strongly
contributes to the deformation behaviour of their specific
panel painting. For the first time, this research has determined
the hygro-mechanical characteristics of panel
paintings by means of experimental tests and numerical
modelling. Due to the large technical differences of
panel paintings, we consider this approach the only possible
one for dimensioning the restraining system on a
scientific basis that should be necessarily adjusted to the
conservation needs of the individual objects.
The Future of Heritage Science and Technologies, 2023
Most panel paintings feature mechanical systems, typically made of
AQ1 crossbeams, designed to co... more Most panel paintings feature mechanical systems, typically made of AQ1 crossbeams, designed to control the distortion of the panel.When the crossbeams are too stiff or too yielding in relation to the distortion tendency of the panel, significant damage to the artworkmay occur. The evaluation of the factors causing thedamage necessarily relies on the restorer’s experience and wisdom; however, in the framework of a long-standing cooperation between Opificio delle Pietre Dure (Florence) and the Research Group on Wood Technology of DAGRI Department (University of Florence), an innovative method has been developed to provide additional objective criteria for dimensioning the crossbeams system. A specific protocol was developed, based on an engineering approach and consisting of the following five “modules”: a) a Restoration Plan, developed by restorers and conservators, b) appropriate mechanical tests to evaluate the stiffness of the painted panel alone and of the crossbeams alone, c) hygroscopic tests to evaluate the hygro-mechanical behaviour of the painted panel alone, d) appropriate numerical modelling for dimensioning the panel-crossbeams system, and e) numerical and/or experimental verification of the dimensioning. This paper describes such protocol and its first implementation on an original panel painting, the Adorazione del Bambino e Committente (in brief called Nativity) attributed to Cesare da Sesto (1514–1515).
Diagnosing wood artworks surface through state-of-the-art high-resolution optical 3D imaging tech... more Diagnosing wood artworks surface through state-of-the-art high-resolution optical 3D imaging techniques " Uwe Noldt Monitoring wood-destroying insects in wooden cultural heritage "
Strain gauges were attached to both faces of 10 mm thick Poplar wood panels before applying a tra... more Strain gauges were attached to both faces of 10 mm thick Poplar wood panels before applying a traditional gesso-based ground layer and varnish on only one face. The application and setting of the ground layer left high strains on both faces of the wood panels. Later measurements, followed by geometrical calculations, showed that for step-humidity changes the strains in the outer surface of the gesso ground layers were small. These results were followed by numerical calculations to indicate the behaviour of thicker panels and with different stiffnesses. These indicated that the strain levels in the ground layer are strongly dependent on the ratio of the thicknesses of the ground layer to the wood, and also weakly dependent on their stiffness ratios. Further calculations showed that the prevention of cupping by mechanical restraint can increase by many times the strains in the ground layer surface, but this also is dependent on the panel thickness. In this paper, the authors have tried to provide some background information about the strains that can result either from moisture changes or from external restraints; to help the conservators make a decision in any specific case.
Lignocellulosic substrates such as wood have been found to have a marked modifying influence on b... more Lignocellulosic substrates such as wood have been found to have a marked modifying influence on both lower-temperature and higher-temperature zones of TTT and CHT diagrams during hardening of formaldehyde-based polycondensates. While the modifying influence of the substrate has been described, the modifying influence of some of the most important manufacturing parameters of the resins on the CHT diagram, not having been previously investigated, are explored here and clear trends are shown. In the case of melamine-urea-formaldehyde (MUF) resins for wood adhesives, the molar ratio (MϩU):F appear to be the dominant parameter influencing the relative position of gel and vitrification curves in relation to each other. The ratio of melamine to urea does not appear to have any effect on the relative position of the curve, lacking any clear trend, at least at the higher (MϩU) molar ratio of 1:1.9 used for this series of resins. In the case presented for the first time, the influence of resin manufacturing parameters on CHT curing diagrams was studied in combination with the modifications introduced by the substrate.
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Papers by Luca Uzielli
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.
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.
tests carried out on wooden panel paintings,
in the context of a close collaboration between the
Opificio delle Pietre Dure and DAGRI (University of
Florence). Starting from the assumption that each panel
painting is a unique entity regarding its composition,
conservation state and history, our approach is now
based on the study of the individual object rather than a
deterministic model. The research considers three main
variables as the origin of the deformation in panel paintings
under climatic variations: the tree ring orientation
of the planks, the emissivity of the paint layer and the
stiffness of the ground layers. The research aim was to
establish a method to determine the deformation behaviour
of panel paintings and the containing effect of the
restraining system, in order to dimension the restraining
system itself on engineering basis. Thus, six Florentine
panel paintings dating from the 14th to the 16th century
were chosen as examples of constituent materials,
construction peculiarities and conservation conditions.
To characterize the panel paintings, each one safely
underwent controlled hygroscopic variations and their
deformation behaviour was measured. The main results
are a) the panel paintings show two different deformation
behaviours, the Flying Wood and the non-Flying
Wood behaviour; b) the paint layers and varnish show
a specific emissivity depending on their specific characteristics;
and c) the stiffness of the ground layers strongly
contributes to the deformation behaviour of their specific
panel painting. For the first time, this research has determined
the hygro-mechanical characteristics of panel
paintings by means of experimental tests and numerical
modelling. Due to the large technical differences of
panel paintings, we consider this approach the only possible
one for dimensioning the restraining system on a
scientific basis that should be necessarily adjusted to the
conservation needs of the individual objects.
AQ1 crossbeams, designed to control the distortion of the panel.When the crossbeams are too stiff or too yielding in relation to the distortion tendency of the panel, significant damage to the artworkmay occur. The evaluation of the factors causing thedamage necessarily relies on the restorer’s experience and wisdom; however, in the framework of a long-standing cooperation between Opificio delle Pietre Dure
(Florence) and the Research Group on Wood Technology of DAGRI Department (University of Florence), an innovative method has been developed to provide additional objective criteria for dimensioning the crossbeams system. A specific protocol was developed, based on an engineering approach and consisting of the following five “modules”: a) a Restoration Plan, developed by restorers and conservators,
b) appropriate mechanical tests to evaluate the stiffness of the painted
panel alone and of the crossbeams alone, c) hygroscopic tests to evaluate the hygro-mechanical behaviour of the painted panel alone, d) appropriate numerical modelling for dimensioning the panel-crossbeams system, and e) numerical and/or experimental verification of the dimensioning. This paper describes such protocol and its first implementation on an original panel painting, the Adorazione del Bambino e Committente (in brief called Nativity) attributed to Cesare da Sesto
(1514–1515).
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.
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.
tests carried out on wooden panel paintings,
in the context of a close collaboration between the
Opificio delle Pietre Dure and DAGRI (University of
Florence). Starting from the assumption that each panel
painting is a unique entity regarding its composition,
conservation state and history, our approach is now
based on the study of the individual object rather than a
deterministic model. The research considers three main
variables as the origin of the deformation in panel paintings
under climatic variations: the tree ring orientation
of the planks, the emissivity of the paint layer and the
stiffness of the ground layers. The research aim was to
establish a method to determine the deformation behaviour
of panel paintings and the containing effect of the
restraining system, in order to dimension the restraining
system itself on engineering basis. Thus, six Florentine
panel paintings dating from the 14th to the 16th century
were chosen as examples of constituent materials,
construction peculiarities and conservation conditions.
To characterize the panel paintings, each one safely
underwent controlled hygroscopic variations and their
deformation behaviour was measured. The main results
are a) the panel paintings show two different deformation
behaviours, the Flying Wood and the non-Flying
Wood behaviour; b) the paint layers and varnish show
a specific emissivity depending on their specific characteristics;
and c) the stiffness of the ground layers strongly
contributes to the deformation behaviour of their specific
panel painting. For the first time, this research has determined
the hygro-mechanical characteristics of panel
paintings by means of experimental tests and numerical
modelling. Due to the large technical differences of
panel paintings, we consider this approach the only possible
one for dimensioning the restraining system on a
scientific basis that should be necessarily adjusted to the
conservation needs of the individual objects.
AQ1 crossbeams, designed to control the distortion of the panel.When the crossbeams are too stiff or too yielding in relation to the distortion tendency of the panel, significant damage to the artworkmay occur. The evaluation of the factors causing thedamage necessarily relies on the restorer’s experience and wisdom; however, in the framework of a long-standing cooperation between Opificio delle Pietre Dure
(Florence) and the Research Group on Wood Technology of DAGRI Department (University of Florence), an innovative method has been developed to provide additional objective criteria for dimensioning the crossbeams system. A specific protocol was developed, based on an engineering approach and consisting of the following five “modules”: a) a Restoration Plan, developed by restorers and conservators,
b) appropriate mechanical tests to evaluate the stiffness of the painted
panel alone and of the crossbeams alone, c) hygroscopic tests to evaluate the hygro-mechanical behaviour of the painted panel alone, d) appropriate numerical modelling for dimensioning the panel-crossbeams system, and e) numerical and/or experimental verification of the dimensioning. This paper describes such protocol and its first implementation on an original panel painting, the Adorazione del Bambino e Committente (in brief called Nativity) attributed to Cesare da Sesto
(1514–1515).