Previous research projects - The Courtauld Institute of Art

Previous research projects

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Wall Painting Conservation

Previous research projects

Previous research projects

A selection of previous departmental research projects:

Analytical techniques

Eugenia Geddes da Filicaia: Field microscopy for invasive analysis. Assessment of polarising microscopes and developments in the methodology for preparing sections and dispersions, MA 2016

Eugenia Geddes da Filicaia
Field microscopy for invasive analysis. Assessment of polarising microscopes and developments in the methodology for preparing sections and dispersions (MA, 2016)

Microscopy is an extremely useful technique for wall painting conservation allowing not only examination of a scheme’s original technique and condition, but also the assessment of past conservation treatments and new interventions. It is a relatively inexpensive and accessible tool, capable of yielding a great variety of information. While it is common practice to collect samples on site and take them back to a laboratory rather than preparing and examining them in situ, this can delay the development of conservation processes. It would clearly be beneficial to the field to move toward an in-situ approach, and the recent development of the Goren microscope, a portable polarising microscope, has seen the potential of in-situ (field) microscopy enhanced.

This study sought first to develop, through rigorous testing of embedding materials and their preparation using portable laboratory equipment, an improved system for the in situ preparation of cross-sections, thin-sections and dispersions.  Samples were prepared from two wall painting sites of differing technology: the earthen-based paintings in Cave 260 of the Mogao Grottoes (China) and the lime-based paintings in Garh Palace at Bundi (India). In order to then assess the results obtainable with the Goren microscope, these samples were examined and imaged both with the portable microscope and with a non-portable research-grade polarising microscope (Leica DMRD). The trials revealed the capabilities of the portable microscope to be extremely encouraging, both in the examination of cross-sections up to 200x and of dispersions and thin sections at much higher magnifications. Furthermore, in trials to assess the capabilities of theGoren microscope for multispectral imaging, it achieved excellent results, successfully imaging UV-induced visibleluminescence, IR-reflected and visible-induced IR luminescence at high magnifications.

Samuel Whittaker: Photo-induced fluorescence imaging to characterise and map natural organic colorants, MA 2013

Samuel Whittaker
Photo-induced fluorescence imaging to characterise and map natural organic colorants (MA, 2013)

Natural organic colorants are widely used in wall paintings either as extracted dyes or lake pigments, employed as translucent glazes or in mixtures with mineral pigments. Despite their widespread use, they have often been overlooked. As organic materials, they are susceptible to deterioration phenomena such as photo-chemical fading and/or alteration, caused by exposure to radiation and pollutants. This susceptibility to deterioration, combined with the fact that they are often applied in low quantities and concentrations, makes their detection and subsequent analysis notoriously difficult. While inspection and imaging using ultraviolet (UV) radiation is a method commonly employed to detect the presence of organic colorants, close similarities in the emissions of different organic colorants makes the use of luminescence imaging as an analytical tool problematic. Imaging that encompasses both UV-induced visible/IR luminescence and visible-induced visible/IR luminescence has greater potential to detect, map and characterize organic colorants.

The present study looks at developing an optimal photo-induced luminescence technique and to define exposure parameters, such as excitation and emission ranges, that will maximise the luminescence for a range of individual colorants so that they can be better mapped and characterised for conservation purposes. Twenty colorants were investigated using UV, visible, IR reflected imaging; UV-induced visible and IR luminescence; and visible-induced red and IR luminescence. In addition IR and UV false-colour images were created. Further, fibre-optic luminescence and reflectance spectroscopy was performed on all the samples, included as a comparison to, and extension of, the imaging, providing valuable information about the reflective and luminescent properties of the colorants.

Austin Nevin: Fluorescence and Raman spectroscopy for analysis of protein-based paint media, PhD 2008

Austin Nevin
Fluorescence and Raman spectroscopy for analysis of protein-based paint media  (PhD, 2008)

The analysis of proteins commonly employed as binding media in paintings using fluorescence and Raman spectroscopy is the focus of this study. Media from eggs (white and yolk), milk (and casein) and collagen-based glues (rabbit skin glue, ox bone glue, parchment glue and isinglass) were considered. Samples made of pure binding media and others of pigment-media mixtures were examined following natural and artificial ageing using spectrofluorimetry and Raman spectroscopy. Fluorescence excitation emission spectra, Laser Induced Fluorescence spectra and Synchronous fluorescence spectra of samples have been recorded and an interpretation of each is provided. An interpretation of the fluorescence of solutions and films of binding media has been suggested based on the presence of different aromatic molecules (amino acids, degradation products) within the different protein-based binding media considered.

It has been shown that fluorescence and Raman spectroscopy can differentiate between films of different binding media and can be used to detect changes that occur on artificial ageing. Using the methods in this study, the identification and discrimination of proteins used as binding media in paintings is challenging due to the presence of inorganic materials in paint, the interaction between pigments and media, and the deterioration of the protein binder on ageing. A critical discussion of results aiming to highlight limitations of the techniques employed is presented alongside recommendations for improvements and further avenues for research. The sample preparation, analytical methodology and data analysis, although specific to this dissertation, could also serve as a guide for future work on similar materials.

 

Published as Nevin et al., ‘The influence of visible light and commonly found inorganic pigments on the autofluorescence of egg, casein and collagen-based media’, Applied Physics A, 92 (2008), 69-76;  ‘Laser-induced fluorescence analysis of protein-based binding media’, Proceedings of the 6th LACONA Conference, Heidelberg, 2007, 309-15;  ‘Time-resolved fluorescence spectroscopy and imaging of proteinaceous binders used in paintings’, Analytical and Bioanalytical Chemistry, 388 (2007), 1897-1905;  ‘Analysis of protein-based binding media found in paintings using laser-induced fluorescence spectroscopy’, Analytica Chimica Acta, 573 (2006), 341-6.

Giovanni Verri: An investigation of corrected UV-induced fluorescence for the examination of polychromy, MA 2007

Giovanni Verri
An investigation of corrected UV-induced fluorescence for the examination of polychromy (MA, 2007) 

Although multispectral imaging – particularly UV-VIS-induced luminescence imaging – is a very common examination tool, its interpretation remains a task fraught with difficulties. In fact, the interpretation of multispectral imaging is strictly connected both to the capture procedure and to an understanding of the physical and chemical characteristics and interactions among materials in the paintings. The nature and interactions of painting materials can be arduous to characterise and analyse, as they vary according to the painting technology and the individual physical histories. Attention has therefore been dedicated to the identification of an appropriate experimental setup which would allow reproducibility of results and comparison of these results in the future.

The experimental setup is designed to be used in situ and allows the capture of UV-VIS-IR-reflected images and of UV-VIS-induced luminescence images. The images captured with the methodology indicated in this study are subsequently analysed via software to create UV-IR false-colour images and to analyse UV-VIS-induced luminescence images. Some of the main issues addressed for luminescence imaging during this study concern the: presence of background ambient straylight; lack of control of the illumination conditions; incorrect representation of the colours of luminescence; and interpretation of phenomena connected to the optical interaction between pigments and binders. The interpretation of phenomena is therefore undertaken on the basis of a rigorous approach to imaging and to a critical evaluation of phenomena with reference to to other investigations, particularly analysis of the paint layer.

The present research, which began with imaging of paint materials of known composition and proceeded to a range of representative case studies, confirmed that luminescence emissions of painting materials – such as organic binders or colorants – can be severely affected by the presence of absorbing non-luminescing materials, such as inorganic pigments. Application of a mathematical model based on the Kubelka-Munk theory, resulted in the possibility of distinguishingbetween real and apparent luminescence emissions. Finally, for Egyptian blue, VIS-induced luminescence in the IR range provided a fast, non-invasive means for the identification of this synthetic pigment.

 

Published as Verri et al., ‘Correction of ultraviolet-induced fluorescence spectra for the examination of polychromy’, Applied Spectroscopy 62(12) (2008), 1295-1302; ‘Post-capture data analysis as an aid to the interpretation of ultraviolet-induced fluorescence images’, in Computer Image Analysis in the Study of Art  (Proceedings of SPIE-IS&T Electronic Imaging, SPIE Vol. 6810), ed. D. G. Stork and J. Coddington, 2008, 1-12.

Austin Nevin: ATR and reflectance micro-FTIR: an exploration of their suitability for the analysis of wall painting cross-sections, MA 2004

Austin Nevin
ATR and reflectance micro-FTIR: an exploration of their suitability for the analysis of wall painting cross-sections (MA, 2004)

This research forms part of the project Organic Materials in Wall Painting coordinated by the Field Projects Department of the Getty Conservation Institute in collaboration with several other conservation science laboratories. The analyses were carried out on samples generously provided by the Tintori Centre. The aim of the project is to develop an analytical protocol for the identification and mapping of organic materials in wall paintings. The protocol will illustrate the flow of investigations from non-invasive (not requiring sampling) to invasive (requiring sampling) that can be used to identify organic materials in wall paintings. The potential and limitations of each investigative technique is evaluated by testing samples of a known composition. The protocol will improve conservation practice by suggesting the extent of information about organic materials present required to plan safe conservation interventions, such as cleaning and consolidation, and the most appropriate set of investigation techniques to obtain it.

 

Published as ‘The use of micro-FTIR with attenuated total reflection for the analysis of wall painting cross-sections’, Zeitschrift für Kunsttechnologie und Konsiervung, 19 (2005), 356-68.

Art historical context

Miriam Gill: Late medieval wall painting in England: content and context (c.1350-c.1530), PhD 2002

Miriam Gill
Late medieval wall painting in England: content and context (c.1350-c.1530) (PhD, 2002)

A large corpus of English wall painting survives from the period c.1330-1530, mostly in parish churches. These paintings constituted a prominent aspect of medieval visual experience, but many extant and recorded murals are fragmentary, abraded and hard to date and identify. There is no published monograph or catalogue for this period and much of the secondary literature is misleading. Consequently, this significant body of visual material has received insufficient attention in the recent historiography of late medieval religious culture and its interpretation has too often been subjective, monovalent and unsystematic.

This thesis examines the deployment and interpretation of wall paintings in late medieval England. It adopts and seeks to refine the traditional tools of context and content. The first part of the thesis focuses on the most important aspects of the context in which murals were created and interpreted: patronage and ideology, reading and reception, and physical context and sacred space. The second part addresses four significant aspects of the content which was novel and prominent in late medieval murals: catechetical subjects, devotional images, memento mori and eschatology, and local saints.

Combining case-studies of important sites with analysis of corpuses of material and generic studies, this thesis suggests that the meaning and significance of mural images could be nuanced, even significantly altered by factors including patronage, ideology, traditions of reading, knowledge of other texts and images, the position of murals and their relationship to other fixtures, rituals and ecclesiastical legislation, as well as to murals and images in other media. The survey of content reveals wall paintings as a multivalent form of visual culture which presented diverse subject matter, varied patterns of reading, a framework for ritual and social relationships and the raw materials for lay spiritual self-sufficiency.

Causes and mechanisms of deterioration

Joshua Hill: Metal soaps in wall paintings: occurrence and assessment, MA 2019

Joshua Hill
Metal soaps in wall paintings: occurrence and assessment (MA, 2019)

Metal soaps remain rarely reported in association with condition phenomena in wall paintings. In contrast, the past two decades have seen a transformed understanding of these materials in easel paintings and association with a range of phenomena including flaking, formation of protrusions, changes in opacity, blanching, and crack formation. For wall paintings, the common issues of extreme environmental fluctuation and presence of soluble inorganic salts could influence the manifestation of metal soap chemistries. This work seeks to assess the importance of metal soaps in wall paintings and identify areas of difference from their manifestation in easel paintings. It does so through multi-analytical examination of suspected metal soaps in archival samples and on newly-obtained samples from case studies at the King’s Stair, Hampton Court and Westminster Abbey chapter house, both painted in oil.

Metal carboxylate aggregates are identified using ATR-FTIR imaging and SEM-EDX of cross sections. While the largest protrusions on the King’s Stair scheme (Verrio, c.1700-02),  were found to be composed primarily of lead (hydroxy)carbonate and pre-date a substantial restoration intervention in the 1960s, others were found to influence the pattern of deterioration of the overlying 1960s varnish. Smaller protrusions were found to contain a higher proportion of lead carboxylates. The paintings in Westminster Abbey chapter house (c.1400) contain substantial passages affected by lead soap protrusions containing variable rations of carboxylate:carbonate, particularly where red lead is present. Ongoing soap activity was found in areas of red lead overlaid with wax, applied as a conservation treatment in the early twentieth century. Since protrusions can readily be misidentified in wall paintings, non-invasive tools are required to distinguish between these causes and to monitor the development of soap-related phenomena. Initial experiments using optical coherence tomography to distinguish between surface protrusions are reported here. This work supports the long-term goal of better understanding the implications of metal soap chemistry for the conservation of wall paintings.

Li Na: A scientific approach to interpreting the damage and ongoing mechanisms of deterioration caused by fire to the wall paintings of the Mogao Grottoes, Dunhuang, China, PhD 2016

Li Na
A scientific approach to interpreting the damage and ongoing mechanisms of deterioration caused by fire to the wall paintings of the Mogao Grottoes, Dunhuang, China (PhD, 2016)

Fire-induced damage occurs to wall paintings worldwide, but variables surrounding such fire events (fuels, combustion mode, duration) and the composition of the artefacts involved (supports, technology, physical history) result in diverse phenomena. The Mogao Grottoes site in north-west China, which comprises some 500 painted Buddhist cave temples dating from the 4th to 14th centuries, includes some 51 caves affected by fire. This research investigates the complex relationship between the paintings’ original materials and fire-induced damage, and the risks inherent to the conservation of these schemes. It is hoped that a better understanding of fire damage will allow a more informed approach to the long-term conservation of fire-affected wall paintings and the avoidance of potentially damaging cleaning interventions.

Five painted caves with representative technologies and fire damage were selected for in-depth study, and the original painting materials and fire-induced alteration characterised. Various levels of blackening, adhesion failure, and alteration of painting components (pigments, organic binders, and renders) were observed. In-situ non-invasive examination and laboratory analysis of micro-samples were undertaken and the morphology of damage categorised to better understand the alteration processes. Based on the prevalence of the chromatic alterations observed, an experiment was devised to explore the role of heat in the alteration of particular copper-based pigments and organic binding media, revealing progressive and irreversible chromatic alteration in the thermal range of 250-500 °C.

Sarah-Jane Fox: Surface deposits on wall paintings: investigating risks, monitoring techniques and preventive or control measures, MA 2016

Sarah-Jane Fox
Surface deposits on wall paintings: investigating risks, monitoring techniques and preventive or control measures (MA, 2016)

Deposition of unwanted, non-original material on cultural heritage objects is a universal conservation problem which has received much attention in the museum environment, yet much of our current knowledge and approaches in this field fails to account for the greater challenges and heterogeneity of materials present at wall painting sites. This research addresses a need for a more comprehensive review of the wide range of materials that are deposited on wall paintings which, due to their size, porosity, complex polychromies, exposure to environmental parameters, and typically lower levels of oversight and management, are exposed to a broader array of risks and greater limitations for monitoring, prevention and control measures.

Drawing on archival records and on-site research, this study presents a comprehensive visual glossary of surface deposits found on wall paintings. Through a review of multidisciplinary literature and analytical investigation, it explores the composition of various deposits, their deposition mechanisms, and the corresponding risks they might pose to original materials. A short survey of UK-based conservation professionals is used to ascertain current monitoring methods and control measures for addressing surface deposits, and selected monitoring techniques reviewed. Replica-based trials using a novel, open-source image analysis tool (Cultural Heritage ImageJ plugin- CHIJ) are undertaken to evaluate its potential for monitoring rates of deposition on wall painting surfaces. Control methods targeting transport and deposition mechanisms affected by air flow, relative humidity, temperature and human activities on site are also evaluated. Underlining the need for a wall painting-specific approach to assessing surface deposits, the author proposes a structured risk assessment framework for determining appropriate strategies for their monitoring, analysis, prevention and control.

Kiernan Graves: An investigation into the technology and behaviour of contemporary murals executed on Portland cement-based supports, MA 2007

Kiernan Graves
An investigation into the technology and behaviour of contemporary murals executed on Portland cement-based supports (MA, 2007)

This research was undertaken to characterise and investigate the techniques and deterioration phenomena of external murals in Los Angeles. This research was limited to investigating murals that are executed on Portland cement-based supports which is the prevailing support for contemporary murals. The research was defined by two phases: source-based research and in-situ investigation of twelve case-studies chosen from well over two hundred murals surveyed throughout the greater Los Angeles area. The paintings’ physical histories, painting technology, condition, and environmental exposure were compiled and assessed.

The three types of painting support most typically observed in this study were poured concrete, concrete masonry blocks adhered with mortar, and concrete render. Analysis revealed most of the paintings to have been executed in water-based acrylic paints applied over a white acrylic primer and covered with a clear protective coating.  While these materials are durable, there are nevertheless aspects of the painting technology that can cause significant condition problems, most notably a lack of interfacial adhesion (particularly at the interface between the support and the primer), cracking and colour change. The findings indicate that paintings executed on poured concrete supports exhibit a greater degree of deterioration to those on other types of concrete, particularly those serving as retaining walls for soil. Failure of interfacial adhesion and cracking were found to result not only from environmental factors but also from the inherent susceptibilities of the original materials, in particular the method of surface preparation.

Robyn Pender: The behaviour of moisture in the porous support materials of wall paintings: an investigation of some environmental parameters, PhD 2001

Robyn Pender
The behaviour of moisture in the porous support materials of wall paintings: an investigation of some environmental parameters (PhD, 2001)

Many forms of deterioration affecting wall paintings can be associated with fluctuating water content in the materials – the stone, plaster, and mortar – which make up their supports. Although it is clear that interstitial moisture behaviour is conditioned by the exterior environment, the relationship to particular parameters such as air movement is not well characterised. Speed of change, and even depth of effect, have yet to be established even roughly. This thesis illustrates the nature of the problems associated with moisture changes in wall paintings, and presents an overview of the theoretical models underlying moisture behaviour in porous materials. A strong argument is made for experimental studies to determine the relative importance of the variables involved. An experiment was developed to monitor the movement of moisture in simplified wall-painting replicas exposed to controlled conditions of humidity and air flow. Replicas were based on stone of different types and permeabilities (Bath and Portland limestone, and York sandstone), and paint layers of low and high permeability.

The final section of the thesis describes and discusses the experimental results, which revealed certain unexpected patterns of behaviour. The type of stone strongly governs speed and pattern of response, with sandstone proving much more permeable than either of the limestones. For all replicas, the tests indicated that in many typical ambient conditions vapour can condense and, in liquid form, move rapidly through the stone. It is hypothesised that this condensation and flow takes place in very fine capillary pathways, most probably the interfacial zones abutting aggregates within the stone. No maximum depth of penetration could be determined for this type of flow; it certainly exceeded the 25 cm thickness of the replicas. In all cases high ambient humidity was found to amplify the degree of moisture exchange with the ambient, evaporation as well as absorption, probably by facilitating the formation of flow paths. Less permeable coatings also exacerbated moisture movement. These results have strong implications for conservation practice, and must now be assessed by examining their impact on deterioration mechanisms such as salt activity.

 

Published as: ‘Towards monitoring moisture movement in the support materials of wall paintings’, in Proceedings of the 6th International Conference on “Non-destructive Testing and Microanalysis for the Diagnostics and Conservation of the Cultural and Environmental Heritage “, I, Rome 1999, 829-41; ‘The behaviour of water in porous building materials and structures’, Reviews in Conservation , 5 (2004), 49-62.

 

Monitoring and assessment

Jorien Duivenvoorden: Environmental data analysis for implementation and evaluation of passive interventions in wall painting conservation, MA 2019

Jorien Duivenvoorden
Environmental data analysis for implementation and evaluation of passive interventions in wall painting conservation (MA, 2019)

The aim of this study was to develop an accessible methodology for environmental data gathering and analysis to facilitate the implementation and evaluation of passive interventions at wall paintings sites. Passive interventions address the activation mechanisms of deterioration and, in the conservation of wall paintings, often involve managing the microclimate, especially with regards to relative humidity as many deterioration mechanisms are related to the recurrent presence of water. The most commonly used methods to control relative humidity for wall paintings or in situ collections are conservation heating, controlled ventilation, absorption, reduction of air exchange or a combination of those. Until now, however, few attempts have been made at assessing the impact of climate control interventions on the environment.

To address this, the study focuses on creating accessible tools for conservators for environmental data analysis. These were developed in R, a free statistical language and environment that is adept at handling large sets of data. These tools were then applied to a case-study, the Sheesh Mahal in Nagaur Fort, Rajasthan (India) where a passive intervention using silica gel to control fluctuating relative humidity levels was implemented and evaluated using the tools developed in R. The study demonstrated that the silica gel intervention has the potential to become a sustainable alternative to heating or dehumidification, both infeasible in Nagaur due to an unreliable power source and the harsh desert environment. Moreover, the study showed that the tools in R are powerful and accessible, enabling the conservator to quickly test a hypothesis, enabling a more iterative approach to the challenging field of in situ conservation.

Wendy Rose: An investigation into the use of photogrammetry as a tool for in situ 3D monitoring of wall paintings, MA 2019

Wendy Rose
An investigation into the use of photogrammetry as a tool for in situ 3D monitoring of wall paintings (MA, 2019)

The field of wall painting conservation has relied on 2D imaging, or ‘photographic monitoring’, to assess rates of deterioration and to determine the efficacy of interventions on wall paintings. However, the capture conditions can be difficult to reproduce and the interpretation of results is highly subjective, with three-dimensional scale impossible to discern on the 2D image. Structure from Motion photogrammetry, which generates 3D point-clouds from images, has the potential to make monitoring more objective and improve the utility of monitoring programmes by recording three dimensions of change rather than two. This research investigates the potential of photogrammetry for in-situ condition monitoring. Agisoft Metashape Professional software was used to generate 3D point clouds and CloudCompare, an open-source free cloud comparison software, employed to detect change between clouds. Time-SIFT, an in-software method of point cloud alignment, was tested as a non-invasive replacement for fixed registration points to align clouds from different capture epochs.

Three trials were undertaken to test the capabilities and limitations of the equipment and workflow. The first aimed to establish the resolution limit of the technique by imaging sandpapers of different standardised grit sizes, while the second trialled the equipment on induced change in plaster patches. A final trial tested the equipment in-situ at St. Botolph’s Church, Hardham to assess the capabilities and limitations at a real wall painting site. While the technique was able to reliably identify change in the order of 500 micrometres, low level noise was found to limit the scale of visible change and in-situ conditions limited the resolution of capture. As a first investigation into photogrammetry as a tool for in-situ condition monitoring, however, the technique has been shown to have significant potential to enhance the level of data collected in a wall painting monitoring programme.

Charlotte Martin de Fonjaudran: Cleaning Asian wall paintings: constraints and development of an open-source analysis workflow for in-situ evaluation of topographical surface changes, PhD 2014

Charlotte Martin de Fonjaudran
Cleaning Asian wall paintings: constraints and development of an open-source image analysis workflow for in-situ evaluation of topographical surface changes (PhD, 2014)

Conservators are often pressured to improve the appearance of objects by removing non-original surface materials. However, cleaning is irreversible and the potential for damage to original materials through repeated interventions is vast. The inherent characteristics of wall paintings that impact their conservation, and cleaning in particular, are explored. Aspects of Asian wall-painting technology are highlighted through targeted analysis of Chinese and Indian schemes and the complexities of cleaning issues at selected sites outlined. Cleaning involves many variables and should follow a set of performance criteria which are clearly defined here. Evaluation during in-situ cleaning trials should allow better-informed choices of parameters (cleaning agent, application and clearance methods). However, trends in conservation science show that current assessment methods are difficult to translate to field practice: they are primarily undertaken in laboratories, on replicas and with invasive analytical techniques. The imaging techniques reviewed here are assessed for in-situcharacterisation of the physical effects of cleaning on a micrometre scale.

While software-based image analysis is increasingly used in cultural heritage conservation, current software and image analysis workflows fail to meet the needs of the conservator.  In this study an image analysis workflow plugin used within the open-source software ImageJ was developed. The comparability of macro images, captured before and after cleaning, is greatly enhanced by corrections for inhomogeneous light distribution, colour discrepancies, lens distortions, chromatic aberrations and camera movement. Analysis of topographical surface changes is undertaken through the creation of pseudo-3D surface plots based on 2D images, the extraction of linear and circular patterns and of zones of specific colours. Quantification of selected features facilitates comparison of the effects of different cleaning trials.  An image- capture protocol adapted to in-situ constraints and image analysis workflow is suggested together with further research to improve current conservation practices for the cleaning of wall paintings.

Fiona Henderson: Dynamic infrared thermography: an evaluation of its potential for wall painting conservation, MA 2013

Fiona Henderson
Dynamic infrared thermography: an evaluation of its potential for wall painting conservation (MA, 2013)

Infrared thermography (IRT) is an imaging technique that detects radiation in the medium- or long-wave regions (2.5-7 and 7-15 µm, respectively) of the electromagnetic spectrum to produce a digital image. It is commonly used to measure temperature variations across an area, with each pixel of the camera’s focal plane array representing a surface temperature measurement. Therefore, this technology has the facility to provide quantitative thermal data and qualitative information about the distribution of temperatures across a surface. The present study investigated the ways in which IRT cameras, operating in the longwave region of infrared, might be usefully employed for wall painting conservation, both for diagnostic investigations and the assessment of remedial interventions.

Following lab-based assessment of a range of Flir cameras and excitation sources, in-situ trials were conducted at Nagaur Fort, Rajasthan, and Tamzhing Monastery, Bhutan, to assess their potential for dynamic applications including the measurement and mapping of thermal effects of insolation and artificial heating, the detection and mapping of cracks and delaminated areas (voids), the investigation of hidden structural features, and for mapping the deposition of grouts and their drying time. Complementary methods of measurement against which dynamic IRT may be assessed were also investigated. The findings of these trials include constraints experienced in the capture and presentation of data and optimal equipment specifications. While the aims of this research were broad, it is hoped that this study provides a sound basis upon which to build more targeted research into the thermal behaviour of wall paintings.

Painting materials and techniques

Elizabeth Woolley: Commercial domination of English ecclesiastical mural painting 1860-1910: demand, supply, technology and significance, PhD 2019

Elizabeth Woolley
Commercial domination of English ecclesiastical mural painting 1860-1910: demand, supply, technology and significance (PhD, 2019)

Commercial decorators dominated ecclesiastical wall painting in England in the period 1860‐1910, a fact noted but rarely explored by commentators; instead, research focusses on well‐documented, technically innovative and relatively rare fine art. This thesis examines the particular demand for ecclesiastical wall painting that was supplied by commercial firms, as opposed to fine artists. It explores the burgeoning numbers of newly‐conceived church decorating companies in the period, their style of wall painting, and their materials. It examines evidence from contemporary literature, commercial archives and the wall paintings themselves.

This thesis describes ecclesiastical commercial decorating in the mid‐nineteenth century, and five ecclesiastical decorating firms in detail: Clayton & Bell; Heaton Butler & Bayne; Hardman; Bell & Almond, and Leach & Sons, including their house styles. It reviews a key nineteenth‐century journal, The Ecclesiologist, to illuminate: i) the then‐current interest in ecclesiastical wall painting, and ii) consequent constraints on church wall painting: tight creative control, prescriptive style and cost effectiveness. Through selected archive research, this thesis reveals the firms’ hierarchical ways of working, and considers allocation of design credit. Archive research generated a large sample population of wall paintings for which geographical reach, trends in commissioning and rates of survival could be traced and extrapolated to the whole corpus. Representative case studies were analysed to establish their material and technical nature. These findings were integrated with the grey literature, creating an alternative to the ‘nineteenth‐century fine art wall painting revival’ technical narrative. This alternative should be a useful context for future conservators and scholars when examining individual schemes of firm wall painting. This integrated and overarching exploration of commercial ecclesiastical wall painting 1860‐1910 allows for a reconsideration of the corpus’s significance, and suggests that it should demand a sensitive and nuanced approach from both a conservation and art historical perspective.

Pu Lan: Tango monastery, Bhutan: a technical study of the wall paintings associated with the shrines of Sambhogakaya and Dharmakaya, MA 2016

Pu Lan
Tango monastery, Bhutan: a technical study of the wall paintings associated with the shrines of Sambhogakaya and Dharmakaya (MA, 2016)

The Kingdom of Bhutan retains an exceptional heritage of Buddhist wall paintings, dating from the early 16th century to the present. Located in buildings that are still in religious use—in temples, monasteries, and dzongs (fortified monasteries), they are relatively inaccessible. Together with the remoteness of Bhutan itself and the lack of an indigenous tradition of art-historical study, the art of the country remains largely unknown. A recent survey of Bhutanese wall painting technology (Shekede and Rickerby 2012) distinguishes the mural schemes at Tango Monastery for their extraordinarily fine technique and condition. Among the most important are the 17th-century paintings which adorn the shrines of Sambhogakaya and Dharmakaya. These paintings, which have only recently come to light, depict the Bodhisattvas and Buddhas of Sukhavati (the Amitabha pure land), together with historical figures connected with the monastery.

The current study was undertaken in relation to the conservation of the wall paintings at Tango by the Courtauld Institute of Art and the Department of Culture of Bhutan, in an attempt to provide a fuller understanding of the wall paintings’ technology and the implications for their conservation. The principal goal of the study was to record, characterise and analyse the painting materials and their application, in particular the complex gilding techniques and the use of glazes, and to investigate workshop practice. Analysis has revealed that the paintings in the two shrines were created with high-quality materials and a complicated palette, a wide variety of gilding techniques and a lavish use of organic colorants and translucent glazes. Furthermore, the paintings are most likely the product of well-organized groups of artists rather than individuals. The painting technique, which displays strong connections with other contemporary Bhutanese wall paintings, is also intimately associated with specific deterioration phenomena which manifest in the paintings.

Stephanie Bogin: A technical study of the early Buddhist wall paintings at Nako, Himachal Pradesh, India, MA 2004

Stephanie Bogin
A technical study of the early Buddhist wall paintings at Nako, Himachal Pradesh, India (MA, 2004)

Nako is located in Upper Kinnaur, a remote region of the Western Himalayas (modern Himachal Pradesh, India) at 3,600 m above sea level, and is home to a Tibetan Buddhist monastic complex dating to the early twelfth century. Two of the temples within the complex, the Lhakhang Gongma and Lotsawa Lhakhang, retain highly important twelfth-century wall paintings. The paintings are particularly significant as early records of the cultural history of the kingdom of Guge-Purang as well as the development of Tibetan Buddhist painting as a result of the second propagation of Buddhism. The present study of the painting technology was undertaken as a preliminary component for the proposed conservation of the site, which has suffered extensive damage and deterioration. The technology of Tibetan Buddhist wall paintings has hitherto received little attention and, as such, there is a great deal of information to be gained from the scientific examination of the paintings at Nako, in particular regarding their affinity with other Asian wall painting traditions.

The original materials of the wall paintings of Lhakhang Gongma and Lotsawa Lhakhang were determined through visual examination, sampling and microscopic analysis, micro-chemical and histo-chemical tests, scanning electron microscopy with energy dispersive x-ray analysis, Fourier transform infrared spectroscopy with attenuated total reflectance, and high performance liquid chromatography. Research to provide contextual support for the findings of the scientific analysis was also undertaken. Through this investigation it has become apparent that the paintings in both the Lhakhang Gongma and the Lotsawa Lhakhang were made with extremely high quality materials and a diverse palette. The Lotsawa Lhakhang in particular demonstrates a highly developed painting technique, reliant on complex application procedures, and the employment of both mixing and layering with a wide range of organic and mineral pigments to achieve subtle visual effects. The identification of a tin-lead alloy (or pewter) leaf made in this study is the first recorded use of this material in wall paintings.

 

Published as ‘A technical study of the early Buddhist wall paintings at Nako, Himachal Pradesh, India’, Zeitschrift für Kunsttechnologie und Konservierung, 19 (2005), 199-230.

Emily Howe: Wall painting technology at Westminster Abbey c.1270-1300: a comparative study of the murals in the south transept and the Chapel of St Faith, MA 2004

Emily Howe
Wall painting technology at Westminster Abbey c.1270-1300: a comparative study of the murals in the south transept and the Chapel of St Faith (MA, 2004)

The wall paintings in the south transept of Westminster Abbey depicting The Incredulity of St Thomas and St Christopher carrying the Christ Child, along with the mural of St Faith in the adjacent chapel, formed part of the far more extensive decorative programme which once embraced this part of Henry III’s sumptuous new abbey. They represent the pinnacle of wall painting practice in England at the close of the thirteenth century and epitomise the transition towards a more complex painting technique born of the pursuit of luminescence. In this study the paintings are subjected to scientific examination for the first time and, in an attempt to inform and limit the extent of sampling required, a range of examination, recording and non-invasive analytical techniques – including in-situ video microscopy, 3-D laser scanning and multispectral imaging in the near-infrared to ultraviolet regions – are trialled.

Analysis reveals that it is in their stratigraphy, rather than their individual components, that the paintings most clearly differ from one other, corroborating stylistic and circumstantial evidence that the two schemes were almost certainly undertaken by different artists. Among the most important findings is the identification of the organic red colorant lac – a costly material not previously identified in medieval English wall paintings, and the discovery of original varnish layers – an component common in panel painting for which conclusive evidence has previously been lacking on wall paintings of such an early date.  Drawing on the findings of these investigations, as well as primary literature and comparative physical evidence, this study attempts to locate both wall paintings more fully in their broader technological context and highlights compelling evidence that, in England at this time, techniques for painting in oil surpassed the boundaries of substrate.

 

Published as: ‘Artistic patronage and painting practices at Westminster Abbey: a comparative study of the murals in the south transept and St Faith’s Chapel’, Burlington Magazine, 148 (2006), 4-14; ‘Wall painting technology at Westminster Abbey c.1260-1300: a comparative study of the murals in the south transept and the Chapel of St. Faith’, in Medieval Painting in Northern Europe: Techniques, Analysis, Art History. Studies in Commemoration of the 70th Birthday of Unn Plahter , J. Nadolny with K. Kollandsrud, M. L. Sauerberg and T. Froysaker (eds.), London 2006, 91-113.

Helen Howard: The pigments of English medieval wall painting, PhD 2000

Helen Howard
The pigments of English medieval wall painting (PhD, 2000)

This study marks the first systematic analysis of the pigments employed in medieval wall paintings in northern Europe, covering an extensive selection of schemes from a variety of sites including parish churches, cathedrals and abbeys (Canterbury, Westminster, Norwich, Winchester, St Albans, Sherborne and Durham). The nature and extent of the palette used is revealed as well as the sophistication with which pigments were applied to achieve differing effects. Thirty pigments are detected including four previously unknown in the context of English medieval wall paintings – vivianite, salt green, kermes lake and madder lake. Also discovered are three alterations of pigments: the lightening of red lead; alteration of vivianite to a yellow form and the transformation of verdigris to a blue chloride-based alteration product. The use of different binding media employed for particular pigments in a single paint layer demonstrates the complex manner in which paintings were executed.

The findings, discussed in the context of wall painting, sculptural polychromy and panel painting techniques in medieval northern Europe, show the broad chronological development in the choice, fabrication and application of materials linked to changes in artistic intent, technology and workshop practice. The analysis undertaken not only reveals the techniques of wall painting in medieval England to have been far more complex than had previously been supposed, but also has significant implications for their conservation.

 

Published as Pigments of English Medieval Wall Painting, London (2003).

Remedial interventions

Mariam Sagaradze: Wall painting conservation trends in Georgian churches: critical assessment and recommendations for an improved approach, MA 2019

Mariam Sagaradze
Wall painting conservation trends in Georgian churches: critical assessment and recommendations for an improved approach (MA, 2019)

Georgia’s cultural identity is intimately associated with Christianity and this is manifest in the country’s rich tradition of ecclesias­tical wall painting which spans more than ten centuries. The painting technology is complex, comprising a heterogeneous range of materials applied in a variety of techniques, and this is reflected in the paintings’ condition. Over the centuries, natural and manmade disasters (such as earthquakes and fire) have taken their toll, and climatic extremes have also provoked various forms of deterioration, leaving many of  Georgia’s wall paintings in a precarious condition. Conservation efforts, largely characterised by a sense of urgency, have catalysed cycles of inappropriate retreatment, bringing many of the country’s mural schemes to the brink of destruction. This study is undertaken as a critical assessment of Georgian conser­vation practices, with a view to improving approaches in the future.

This study marks the first attempt to systematically collate documentation relating to ecclesiastical wall painting conservation in Georgia from the 1900s through to the 2010s. Based on extensive archival research and interviews with Georgian paint­er-restorers working in the field, a database has been developed to facilitate interpretation of the paintings physical history and current condition which, it is hoped, will serve as a valuable tool for the Georgian conservation community in devising better informed interventions. Critical analysis of the information gathered has revealed a heavy and sustained reliance on re­medial interventions, as well as a lack of understanding of original technology and conservation materials and their behaviour. The study proposes an improved methodological approach for the assessment of wall paintings in Georgia, based on well-established scientific principles and an emphasis on minimal interven­tion. The six-step methodology, which is trialled as a case-study at the Church of Archangels in Zemo Krikhi, is based on an iter­ative process of investigation which asserts the informed conservator as central in assessing a painting’s conserva­tion needs.

Chiara Pasian: Non-structural lime-based injection grouts with reduced water content for decorated surfaces, PhD 2017

Chiara Pasian
Non-structural lime-based injection grouts with reduced water content for decorated surfaces (PhD, 2017)

Wall paintings are complex, multi-layered porous systems often suffering from failure of adhesion between plaster layers. Failure can be stabilised with injection grouting, introducing a compatible adhesive material with bulking properties and water as suspension medium. Water is required for chemical setting and in the improvement of injectability. However, the introduction of excessive amounts of water may lead to segregation, shrinkage and failure. Water can be dangerous when water-sensitive original materials are present and can cause the solubilisation of salts which, upon re-crystallisation, have the potential to cause severe disruption to the original painting materials.

Water-reduced injection grouts were designed to investigate the use first, of ethanol as a partial substitute for water and second, of ovalbumin (a water-soluble protein found in egg white) as a water reducer which also serves to improve rheology. The working properties of these grouts in the fluid state and performance of the set grout were tested in the laboratory. The influence of ethanol and albumin on chemical reactions were assessed with X-ray powder diffraction coupled with quantitative phase analysis (XRPD-QPA). The internal structure of the set materials was investigated with scanning electron microscopy with EDS microanalysis (SEM-EDS) and porosity with X-ray micro-computed tomography (X-μCT). The influence of lime and ethanol on albumin was studied with Matrix Assisted Laser esorption/Ionisation Time of Flight (MALDI-TOF). The water-reduced grouts developed in this study displayed properties suited to use on site, displaying high porosity, good cohesion and adhesion, high water permeability, adequate flow and minimal shrinkage, and the advantage of a considerable water reduction.

Denise Invamoto: The interface between conserving structures and wall paintings, MA 2016

Denise Invamoto
The interface between conserving structures and wall paintings (MA, 2016)

Though wall paintings are inseparable, physically and contextually, from their supporting structures, the interface between conserving structures and wall paintings is often neglected. This study considers the risks that interventions to the structure pose to wall paintings and explores ways in which more integrated projects might be promoted. An overview of the intersections between building behaviour (structure and building envelope) and wall paintings is presented and the specificities of conserving wall paintings highlighted. In surveying the potential damage and activation of deterioration mechanisms to wall paintings that building interventions can cause, and with particular reference to St Mary’s church at Houghton on the Hill (Norfolk), the study promotes a more holistic understanding of buildings and their contents.

Aspects of the conservation framework (principles, legislation and policies) and elements of integrated conservation projects are also investigated, with reference to two specific case-studies: Richmond Castle Detention Block and the Painted Hall of the Old Royal Naval College, Greenwich. Through interviews with wall painting conservators, building conservators, heritage officers, stakeholders and grant-aid officers, the English context is thoroughly explored to illustrate the complexity of interactions between technical aspects, the conservation framework and project development contexts. Research makes clear that wall paintings are susceptible to damage and deterioration caused or worsened by building works and that appropriate methods, materials, definition of sequence and planning of interventions could prevent many of these risks. This findings of this study reinforce the conclusion that the conservation requirements of the wall painting must be incorporated in the overall design and development of the building project, with integration, communication and awareness at every level between the professionals involved.

Juana Segura Escobar: Sorbent and abrasive: critical assessment of the potential role of sponges in the conservation of wall painting, MA 2010

Juana Segura Escobar
Sorbent and abrasive: critical assessment of the potential role of sponges in the conservation of wall painting  (MA, 2010)

Sponges are auxiliary materials used ubiquitously in conservation. They are porous structures that can be used dry or wet as an abrasive and/or sorbent, and are employed mainly for cleaning and clearance purposes with other less frequent applications. Despite their wide use in conservation they have been remarkably little studied. The present study aims to respond to the challenge of a plethora of poorly characterised sponges on the market and in widespread conservation use, while addressing the specific constraints imposed by wall paintings. It will also investigate the potential of synthetic swabs, which currently enjoy a much more limited use in wall painting conservation.

Based on a preliminary survey of sponges currently used in conservation practice, a selection of materials for investigation was made comprising three latex-based, four poly(vinyl formal), and eight melamine sponges, and ten types of swab. In order to determine the sorption properties of the sponges, dry and wet densities were measured as well as wicking properties, absorption maxima and desorption behaviour. The deposition of sponge residues due to mechanical action was assessed by abrasion tests on MicroMesh™ of various grades (500, 1000, 2400 and 4000) observed under high magnification and with UV light, while chemical residues were evaluated using ATR-FTIR. The resistance of the sponges to chemicals commonly used in conservation was also explored. Subsequent to lab trials, in situ testing of two sponges was undertaken on the wall paintings in the Sheesh Mahal in the Fort of Nagaur, India. The PVF Astonish™ Watermate® sponge was trialled as a poultice for salt extraction in the vault, while the melamine Meleco® Magic Sponge was used for clearing after cleaning with reagents applied in gel on a replica made in the same technique as the wall paintings at the Sheesh Mahal.

 

Published as ‘Sorbent and abrasive: a critical assessment of the potential role of proprietary synthetic sponges in conservation’, Zeitschrift für Kunsttechnologie und Konservierung 27 (2013) 269-83.

Amarilli Rava: Adhesion failure in wall paintings: a methodological approach to the remedial intervention, MA 2010

Amarilli Rava
Adhesion failure in wall paintings: a methodological approach to the remedial intervention (MA, 2010)

Flaking is a widespread deterioration phenomenon affecting wall paintings, occurring on a variety of supports and in a wide range of environments. Traditionally, lack of adhesion in wall paintings is addressed by treatment with adhesives, consolidants or coatings. While adhesives themselves have been evaluated in a number of studies, there remains very considerable scope for investigation of the complexities of the readhesion intervention. The present study looks specifically at adhesion failure between paint and/or preparatory layers and their support. It aims to provide a basis for the construction of a general methodology for understanding the deterioration phenomenon and designing and implementing the remedial treatment.

The study explores the concept of adhesion and the characteristics of flaking, which play a central role in the design and implementation of the remedial treatment. The long- and short-term requirements of adhesion interventions are investigated and described, together with the physical and chemical parameters that circumscribe the treatment. Laboratory-based performance assessment is undertaken during three principal phases in adhesion interventions, namely: 1. while the applied material is in liquid state; 2. during hardening/setting of the adhesive (gel state); and 3. after hardening or setting of the adhesive. Methods for post-treatment evaluation include macro- and micro-observation, water absorption testing and the assessment of adhesive deposition using SEM. Based on the findings of these trials, in situtreatment trials are subsequently undertaken at Richmond Castle detention block, an English Heritage site with extensive areas of badly flaking limewash bearing historically important graffiti from the First and Second World Wars.

Elizabeth Woolley: Covering and concealing wall paintings: an investigation into rationales and methods, MA 2010

Elizabeth Woolley
Covering and concealing wall paintings: an investigation into rationales and methods (MA, 2010)

Covering and concealing interventions, resulting in wall paintings being obscured from view, are rarely documented in the published record. This lack of documentation is further compounded by the absence of an established terminology for this common intervention. In practice, the intervention is often undertaken without approval of the appropriate authorities or even the involvement of a conservator. Consequently, the obscured painting is at a significantly increased risk of destruction, it very existence undocumented. Research undertaken as a prelude to this study reveals that paintings are most commonly covered for aesthetic or financial reasons rather than their preservation, and that there is dissatisfaction among conservators regarding current covering practices.

This study has sought to develop a more rigorous methodology for approaching the covering and concealing of wall paintings. Performance criteria were established for both covering and concealing, and, based on these, an assessment of selected case-studies conducted, including excavated wall paintings in the 2nd-century amphitheatre at Caesarea (Israel),  the 17th-century decorative paintings in Norre Åby, Denmark, and 17th-cntury marbled panels in Chastleton House, Oxfordshire. These cases demonstrate that covering and concealment interventions, if well designed, can preserve wall paintings indefinitely. The importance of post-intervention assessment is highlighted as an integral part of the long-term performance of coverings and concealments, since it is through continued inspection that the painting’s existence remains known, and the greatest risk to obscured paintings – that of inadvertent destruction – diminished.

Charlotte Martin de Fonjaudran: Removing non-original varnishes from two oil-based wall paintings: an investigation of the intervention criteria and assessment of selected cleaning methods, MA 2004

Charlotte Martin de Fonjaudran
Removing non-original varnishes from two oil-based wall paintings: an investigation of the intervention criteria and assessment of selected cleaning methods (MA, 2004)

This study investigates the removal of degraded non-original natural resin varnishes from oil-based wall paintings by exploiting the greater knowledge and experience of varnish removal available in the field of easel painting conservation and adapting it to the demands of in-situ wall painting conservation. Conservation issues related to varnish application and removal from wall paintings are summarised, along with the present state of knowledge of the cleaning mechanisms of solvents, alkaline reagents and resin soaps. The criteria for the intervention of varnish removal, both its performance characteristics and working properties, are outlined. Investigations and trials performed on the Baroque paintings of Reigate Priory (Surrey) and of the church of Our Lady of Victory, Valletta (Malta) form the core of this study. Analyses of the original and added materials were carried out for both paintings and their state of conservation evaluated in order to inform the selection of cleaning agents and appropriate auxiliary materials (sorbents).

Assessment of the cleaning trials with regard to the performance characteristics of the intervention was carried out both on site and by means of SEM and cross-section examination of samples taken before and after treatments with various cleaning materials and methods involving mechanical action (swabbing), reduced mechanical action (gel) and without mechanical action (absorbent tissue). Organic analysis using DTMS and gas chromatographic techniques was undertaken to obtain further insight into the impact of the cleaning agents—deoxycholic acid resin soap, acetone, N-Methyl-2-Pyrrolidone and dilute ammonia—on the various components of the varnishes and to compare the cleaning actions of the different systems. In both cases complete removal of the varnishes was not achieved and thin varnish films, whose thickness and surface topography varied according to the application methods, were observed. Whether cleaning ought to reach complete removal of the coatings has to be assessed, weighing the potentially highly damaging impact of certain cleaning agents on the original materials against the slow increase in yellowing and insolubility of the remaining varnish.

Sibylla Tringham: Characterising the deposition of acrylic consolidants in painted lime plaster, MA 2004

Sibylla Tringham
Characterising the deposition of acrylic consolidants in painted lime plaster (MA, 2004) 

Consolidation is a remedial intervention which addresses the loss of cohesion within a paint layer, support or both.  Consolidation refers specifically to the problem of powdering due to a loss of cohesion between individual particles or small clusters of particles, and aims to re-establish cohesion within porous, loosely bound material by introducing an organic or inorganic substance which acts as a replacement binder. Many past consolidation interventions have failed due to the materials used and/or the method of application however, acrylics have gained popularity recently due to their apparent stability and their versatility in application, yet their deposition within porous substrates is poorly understood. Examining the deposition of consolidants is complicated by problems in accurately identifying the presence of consolidating material within a porous substrate. The present study was designed to characterise the deposition of some acrylic consolidants, as well as the initial penetration of the system, in painted lime plaster and to evaluate a range of methods to achieve this.

While many variables affect the penetration of the system and final deposition of the consolidant, the study targeted the effects of system type (solution or aqueous dispersion), solvent type and concentration. The acrylics selected for study were Paraloid B72™, and the aqueous dispersions Plextol B500™ and a new consolidant, Medium for Consolidation™ (MFC). Acetone and 1- methoxypropan-2-ol (PGME) were selected as solvents with divergent properties; and 2% and 6% solids were selected as exhibiting either end of the range typically used in consolidation.  System penetration was assessed using a system dye. Consolidant deposition on a macro scale (mm) was examined using the iodine vapour method and drilling force resistance. On a micro scale (µm) the deposition was examined with SEM. The effect of temperature on in-situconsolidants was also assessed with ESEM, and reflectance spectrometry provided data on the changes in surface reflectance produced by the consolidants. Tests revealed that penetration of the system was deeper than the deposition of the consolidant and that consolidant dispersions were deposited further in depth than solutions resulting in higher cohesive strength and producing less change in reflectance. Higher concentrations resulted in higher cohesive strength, deposition further in-depth and a greater change in reflectance.

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