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Photochemical colour change for traditional watercolour pigments in low oxygen levels
Abstract
An investigation for light exposure on pigments in low-oxygen environments (in the range 0-5% oxygen) was conducted using a purpose-built automated microfadometer for a large sample set including multiple samples of traditional watercolour pigments from nineteenth-century and twentieth-century sources, selected for concerns over their stability in anoxia. The pigments were prepared for usage in watercolour painting: ground and mixed in gum Arabic and applied to historically accurate gelatine glue-sized cotton and linen-based papers. Anoxia benefited many colorants and no colorant fared worse in anoxia than in air, with the exception of Prussian blue and Prussian green (which contains Prussian blue). A Prussian blue sampled from the studio materials of J.M.W. Turner (1775 - 1851) was microfaded in different environments (normal air (20.9% oxygen) 0, 1, 2, 3.5, or 5% oxygen in nitrogen) and the subsequent dark behaviour was measured. The behaviour of the sample (in normal air, anoxia, and 5% oxygen in nitrogen) proved to be consistent with the 55 separately sourced Prussian blue samples. When exposed to light in 5% oxygen in nitrogen, Prussian blue demonstrated the same light stability as in air (at approximately 21 degrees C and 1 atmosphere). Storage in 5% oxygen is proposed for 'anoxic' display of paper-based artworks that might contain Prussian blue, to protect this material while reducing light-induced damage to other components of a watercolour, including organic colorants and the paper support.
... The paint mock-ups allow to reproduce the original hues by using historical recipes and procedures and may aid in the interpretation of the analytical results obtained from the analyses of actual cultural heritage objects [18]. MFT has been extensively used to test the lightfastness not only of cultural heritage objects, but also reference mock-up samples containing cultural heritage materials such as watercolour paints applied on paper [19], ballpoint pen inks [20], textile samples [21,22], and Prussian blue pigment across samples applied on cotton and silk substrates [23], among others. ...
... The spectrometer used is a Jaz miniature device with the SpectraSuite® spectrometer operating software (Ocean Optics, Florida, US). A detailed measurement configuration can be found elsewhere [9,[19][20][21][22][23]27]. ...
... Most apparent is the darkening of paper supports, the fading or darkening of emerald green in dilute passages, and the dulling of organic reds [5]. Watercolor and gouache are traditionally classified as sensitive to light [6][7][8], and the literature indicates that water-based paints can differ in their lightfastness [9][10][11]. Previous research by Zieske [12,13] investigated the pigments and papers used by Cezanne in nine watercolors in the collection of the Philadelphia Museum of Art (PMA) executed between c. 1877 and 1904, where the following pigments were identified by energy dispersive X-ray spectrometry (EDS): lead white, vermilion, red lead, iron oxides, chrome yellow, emerald green, viridian, and cobalt blue; ultramarine and organic pigments were inferred based on the absence of other detectable elements and the observed color. ...
... After pigment identification, microfade testing (MFT) was done to gauge the light sensitivity of the watercolors in their current state. The use of MFT on watercolors has become a relatively common practice [10,11,[18][19][20][21] to better assess the light sensitivity of what has been traditionally considered one of the most light-sensitive media. ...
The exhibition Cézanne Drawing at The Museum of Modern Art (MoMA) brought together an exceptional group of works on paper from public and private collections across the globe. Recognizing the inherent light sensitivity of both the paper and watercolors, controlling, and tracking light exposure was central to the exhibition planning. This concern also led to a systematic study of three watercolors in the museum’s collection, Foliage (1895), Study of Trees (1895), and Mont Sainte-Victoire (1902-06), to characterize the watercolor paints used by Cezanne in these works and their sensitivity to light exposure, and to better understand the condition of the drawings based on the palette’s chemistry. Examination and analysis were undertaken non-invasively and micro-invasively with the following techniques: Infrared Reflectography (IRR), Ultraviolet Fluorescence Photography (UVF), Raman and surface-enhanced Raman (SERS) spectroscopies in addition to X-Ray fluorescence analysis on small spots and large areas using portable (p-XRF) and XRF scanning, respectively. The palette for these three watercolor drawings includes lead white, bone black, vermilion, yellow ochre, chrome yellow, emerald green, viridian, cobalt blue, and synthetic alizarin and carmine lakes. Microfade testing (MFT) was performed on the paper support and spots with each identified pigment, and the data acquired was evaluated both for color change (ΔE00) and rate of color change (∂ΔE00∂t). Together these techniques inform the future display and loan of these and similarly fugitive watercolors in Cézanne’s oeuvre.
... Among all the factors other than illuminance, oxygen has been the most studied environmental factor in the research on pigments and dyes. It has been found that anoxia and hypoxia can benefit the majority of the unstable colourants [31], except for metal-containing colourants [32]. Furthermore, Ford [6] seems to be the only research that has taken the effect of RH into consideration but did not observe a significant effect of RH on the discolouration of iron gall ink. ...
... Low [O 2 ] and high RH was observed to have induced the largest absolute k ΔR , suggesting the discolouration of iron gall ink is likely to be promoted in an anoxic and humid environment. The promotional effect of anoxia on discolouration has been observed not only for historical iron gall ink in another independent research [6], but also for another iron-containing pigment -Prussian blue [15,31,37]. Research on the chemistry of Prussian blue reveals that its colour intensity arises from the charge transfer transition from Fe (II) to Fe (III) in the Fe (III) -N-C -Fe (II) moiety [38]. ...
The causes of the discolouration of iron gall ink have been debated for decades. As a contribution to the understanding of the photodegradation behaviour of iron gall ink, this paper discusses the effects of three environmental factors that are of primary concern – oxygen, moisture and light. Using a range of historical paper-based samples, a 2³ full factorial experiment was designed to quantify the effects of oxygen concentration [O2], relative humidity (RH), illuminance (Ev) of broadband LED light, and their interactions. A change in diffuse reflectance with time was observed to mainly take place beyond 600 nm into the NIR range. The change followed similar patterns under all the experimental conditions, which was modelled by a logarithmic relationship with time of degradation. The rate constant was obtained and was found to be mainly affected by [O2], RH and their interaction. The role of Ev needs further investigation, however, its insignificant effect on the discolouration measured in this research suggested the possibility of effective degradation control with relaxed lighting controls. Furthermore, the wavelength sensitivity of iron gall ink's discolouration was investigated using narrowband radiation centred at three different wavelengths (Λ): 450 nm ([Λ450]), 525 nm ([Λ525]) and 625 nm ([Λ625]), with varying [O2] and RH. RH, Λ, the interaction between RH and Λ, and the interaction between RH and [O2] were found to have strong effect on the rate constant of discolouration. Among these factors, Λ showed the strongest effect, which decreased as Λ increased. Approximately 3x and more than 10x faster degradation by [Λ450] than [Λ525] and [Λ625] respectively was observed, which was likely to be associated with photon energy and quantum efficiency in absorption at different wavelength.
... The binder plays a role in pigment degradation under anoxic conditions, with the greatest colour stability observed for the oil colour, followed by the water colour and pure dye on paper. [15][16][17][18] In addition, Bowers and Sobeck have reported 19 a comprehensive study on the photoaging of CA and its lake as a function of different experimental parameters such as oxygen content, humidity and binder. However, several aspects of the mechanisms of CA photodegradation still need to be addressed. ...
... Readers with a more extensive interest in the fading of watercolours may consult the following publications:Cohn (1977) marks an early study;Saunders (1994) surveys pigment sensitivities andLerwill et al. (2015) also features a discussion of the effect of low oxygen levels on fading.Didactic Fading Panel ...
A small framed display panel holds a selection of paper and media common in works on paper plus a set of Blue Wool Standards. The selection of materials and design of the panel including two types of glazing are presented, and the purpose of the panel as a tool for explaining the effects of light on materials is discussed. At the centre of the panel are watercolour samples prepared using primary colours in mixed washes that illustrate hue shift resulting from selective fading of one colourant.
... Obviously, the presence or absence of oxygen plays a major role in the photodegradation process of dyes and pigments. Multiple studies have shown that in most cases of organic colorants, a decrease in oxygen concentration leads to lower photodegradation rates, however, a complete halt to the fading process has not been observed [48,57,[64][65][66][67][68][69][70][71]. This might be due to other degradation processes occurring simultaneously (e.g., reduction in presence of a reducing agent). ...
It has been known for many years that dyes and pigments are subject to light-induced degradation, or photodegradation, when exposed to light. It is the very reason why some beverages or medicines are wrapped in light-tight packaging materials, and why museums cover their windows with UV-blocking filters. The exact chemistry of light-induced degradation can be quite complex. Why and how are these dyes and colorants affected by light? How fast do these processes occur? Are there ways to prevent this from happening in a straight-forward and durable way? These were and still are questions that are relevant to the many fields where colorants are applied. In order to support these questions, we have tried to provide a broad overview of the research that has already been conducted on photodegradation of dyes and pigments and the analysis of photodegradation products. In those papers, the most important parameters that were discussed are the influence of the irradiation source, intensity and time, the presence or absence of oxygen, temperature, the effects that catalysts have, as well as the dye or pigment concentration. Additionally, we have investigated the differences found for photodegradation in solution and on substrates and specific parameters that may affect the processes in these media.
... According to current knowledge, low-oxygen microenvironments are the most effective method for preserving pyritic material (Allington-Jones and and also certain types of meteorite, polymers (Dyer et al., 2011) and organic material such as works of art on paper (Lerwill et al., 2015;Tate, 2012). Large-scale storage projects have been undertaken by several museums in recent years (e.g. ...
The cost in damage caused to earth science collections by pyrite oxidation is well known. But what are the costs of re-housing specimens in low-oxygen microenvironments? This article explores the financial, temporal and spatial costs of a re-storage project, in an attempt to aid collections management planning.
... By adjusting the proportion of four narrowband lights with different peak wavelengths of red, amber, green, and blue, the RAGB (red + amber + green + blue) type of the four primary white light-emitting diodes (fp-WLEDs) meeting the above requirements can be obtained [7]. Due to different response rates of organic pigments to different wavelengths of visible light and the flexible spectrum composition of the fp-WLEDs, the extent of the illumination-induced damage to high-light-sensitivity art caused by the fp-WLEDs with different spectral power distributions (SPDs) varies considerably [8][9][10]. With increasing application of the fp-WLEDs in museums, it is urgent to evaluate the illumination-induced damage to organic pigments caused by the four narrowband lights mentioned above so as to evaluate the illumination-induced damage to high-light-sensitivity art caused by the fp-WLEDs with different SPDs in the light environment of museums. ...
Because commonly used organic pigments are highly responsive to visible light, high-light-sensitivity art is vulnerable to irreversible illumination-induced damage caused by radiation from light sources. With application of the four primary white light-emitting diodes (fp-WLEDs) in museums, it is urgent to evaluate the illumination-induced damage to high-light-sensitivity art caused by the fp-WLEDs. Four narrowband LEDs with different peak wavelengths of 450, 510, 583, and 650 nm that constitute the spectra of the fp-WLEDs were used to irradiate three commonly used organic pigments: safflower, gamboge, and indigo. Based on the fundamental reason for the illumination-induced damage, that is, photochemical reactions, Raman spectroscopy was introduced into the study. The Raman spectra of pigments were measured before and after illumination. The characteristic Raman peaks corresponding to the functional groups that determine color and structure of pigments were selected, and the variations in their peak intensities were calculated. The illumination-induced damage coefficients of four narrowband LEDs on three organic pigments were obtained, providing a data basis for illumination-induced damage evaluation equation proposed in this study, which was expected to further realize museum admission evaluation of the new fp-WLEDs.
... The binder plays a role in the pigment degradation under anoxic conditions, with the greatest colour stability observed for the oil colour, followed by the water colour and pure dye on paper. [15][16][17][18] In addition, Bowers and Sobeck have reported 19 a comprehensive study of the photo-aging of CA and its lake as a function of different experimental variables such as oxygen content, humidity and binder. However, several aspects of the mechanisms of CA photodegradation still need to be addressed. ...
Carminic acid (CA) and other related compounds have been widely used as dyes in cultural heritage, cosmetic and food industry. Therefore, the study of their properties upon photoexcitation is particularly important. In this work, the photophysical and photochemical properties of CA, Carminic Lake and other related pigments in aqueous solutions are revisited. Novel quantitative information regarding the fate of the photoexcited states is provided including the efficiency of reactive oxygen species (ROS) photosensitized production (i. e., singlet oxygen and hydrogen peroxide) as well as the efficiency of the nonradiative deactivation pathways. Laser-induced optoacoustic spectroscopy (LIOAS) data reveal that, for all the investigated compounds, almost all the absorbed energy is released as prompt heat to the media. This is in agreement with the fact that other deactivation pathways, including fluorescence (ΦF ̴ 10-3 – 10-5), photochemical degradation (ΦR ̴ 10-4) and/or photosensitized ROS formation (ΦH2O2 < 10-5 and ΦΔ ~ 0), are negligible or null. In addition, a comprehensive investigation of the photodegradation of CA and Lake is herein reported. The influence of different experimental parameters such as irradiation wavelengths and oxygen partial pressure was evaluated. UV-vis absorption and fluorescence emission spectroscopy in combination with chemometric data analysis were used to elucidate relevant aspects of the photodegradation mechanism involved and to elucidate the spectroscopic features of the photoproducts generated. In aqueous media, CA follows an O2-dependent photochemical degradation when subject to elapsed photoexcitation in the UVB, UVA and visible regions. The photoproduct profile depends on the excitation wavelength giving rise to quite distinctive spectroscopic profiles. With respect to Lake, our data suggest that upon photoexcitation this pigment releases a CA-like chromophore that follows a similar fate than CA.
... Over the past two centuries, it turned out that these objects are not only threatened by war or robbery but also from a completely different angle, i.e. exposure to light (Staniforth, 2013). In this regard, there must be a set of specific lighting factors that have the highest quality in displaying fine artworks and also to protect them by controlling light damage (De Graaf et al., 2014;Lerwill et al., 2015). Research across various types of projects are surveyed. ...
Purpose
The purpose of this study is to identify effective lighting criteria in the museum from two theoretical and practical points of view.
Design/methodology/approach
Assessment of theoretical and practical weight of criteria was taken with the aim of concurrent attention in scientific and executive. Finally, ten effective criteria were identified by the Pareto chart.
Findings
The findings of this study represents a centralized reference source of the most important criteria and also effective guidance to improve the lighting quality and effective guideline to improve the lighting quality and operational fluency.
Practical implications
The paper can help the lighting experts, contemporary designers and future researchers to enhance the lighting function in art museums and design based on needs as well as up-to-date techniques.
Originality/value
Lighting as a fundamental element in the existing art museum has a significant impact on the better understanding of the artworks by the viewers. On the other hand, according to the importance of protecting valuable museum artefacts, lighting can have an effective or destructive impact on them directly. But with consideration of different museum lighting, there is a large range of effective lighting criteria that can choose the right methods harder.
... Watercolours are produced by the combination of a pigment with gum Arabic and other substances not specified by the manufacturer to safeguard the industrial patent [23][24][25][26][27][28]. The necessity to investigate the stability of retouching products is linked to the unknown and unpredictable behaviour of the commercial mixtures whose composition is not declared by suppliers [19,[29][30][31][32]. Though watercolours are widely used in conservation, their stability in the long run has not been sufficiently studied [33][34][35][36][37][38] or it is limited to the investigation of pigment modification without examining the binder behaviour [39]. In general, even if retouching is a consolidated praxis in restoration, the monitoring of behaviour of retouched artworks is not widely applied, especially due to the high costs or lack of maintenance programs. ...
The aim of this work is to present the utilization of Hyperspectral Imaging for studying the stability of painting samples to simulated solar radiation, in order to evaluate their use in the restoration field. In particular, ready-to-use commercial watercolours and powder pigments were tested, with these last ones being prepared for the experimental by gum Arabic in order to propose a possible substitute for traditional reintegration materials. Samples were investigated through Hyperspectral Imaging in the short wave infrared range before and after artificial ageing procedure performed in Solar Box chamber under controlled conditions. Data were treated and elaborated in order to evaluate the sensitivity of the Hyperspectral Imaging technique to identify the variations on paint layers, induced by photo-degradation, before they could be detected by eye. Furthermore, a supervised classification method for monitoring the painted surface changes, adopting a multivariate approach was successfully applied.
... It is being used as a routine method for testing iconic objects and documents, for screening out highly light-sensitive items from going on exhibit or on loan Smith 2010, 2011b;Tse, Cipera, and Leckie 2011;Townsend, Ford, and Townshend 2013;Eng, Preusser, and Schaeffer 2016), for surveying photographic material (Freeman et al. 2014) and natural history collections (Tse, Cipera, and Leckie 2011;Ford and Druzik 2013), Alaskan native artefacts (del Hoyo-Meléndez and Mecklenburg 2010), textile dyes (del Hoyo-Meléndez and Mecklenburg 2012), and Japanese wood block prints (Connors et al. 2005). It is also used for research (Pearlstein and Keene 2010;del Hoyo-Meléndez and Mecklenburg 2011;Beltran and Druzik 2012;Ford 2014;Lowe et al. 2014;Lerwill et al. 2015aLerwill et al. , 2015bLerwill et al. , 2015cPesme et al. 2016;Ford and Smith 2017), to complement other analytical techniques (Columbia et al. 2013;del Hoyo-Melendez et al. 2016;Troalen et al. 2016), and for risk assessment (Pesme 2016). ...
Since 2008, the Canadian Conservation Institute (CCI) has provided microfade testing (MFT) as a service to more than 13 Canadian museums, archives, and galleries. In addition to obtaining lightfastness data for objects and collections planned for exhibition, MFT is also used for research and for training. This article summarizes the experiences and practices that arose from the variety of objects tested, the demand for the service, and the lessons learned. These include protocols to ensure reliable and reproducible results with multiple users, ways to report large number of results, and how MFT data are used with the CCI Light Damage Calculator for effective communication of the results with other museum staff for exhibit planning.
... Though watercolours are widely used in conservation, their stability in the long run has not been sufficiently studied [15][16][17][18][19][20][21] or is limited to the investigation of pigment modification without examining the binder behaviour [22]. In general, even if retouching is a consolidated praxis in restoration, the monitoring of behaviour of retouched artworks is not widely applied, especially due high costs or lack of maintenance programs. ...
The aim of this work is to investigate the stability to simulated solar radiation of some paintings samples through a new methodological approach adopting non-invasive spectroscopic techniques. In particular, commercial watercolours and iron oxide based pigments were used, these last ones being prepared for the experimental by gum Arabic in order to propose a possible substitute for traditional reintegration materials. Reflectance spectrophotometry in the visible range and Hyperspectral Imaging in the short wave infrared were chosen as non-invasive techniques for evaluation the stability to irradiation of the chosen pigments. These were studied before and after artificial ageing procedure performed in Solar Box chamber under controlled conditions. Data were treated and elaborated in order to evaluate the sensitivity of the chosen techniques in identifying the variations on paint layers, induced by photo-degradation, before they could be observed by eye. Furthermore a supervised classification method for monitoring the painted surface changes adopting a multivariate approach was successfully applied.
... It is being used as a routine method for testing iconic objects and documents, for screening out highly light-sensitive items from going on exhibit or on loan Smith 2010, 2011b;Tse, Cipera, and Leckie 2011;Townsend, Ford, and Townshend 2013;Eng, Preusser, and Schaeffer 2016), for surveying photographic material (Freeman et al. 2014) and natural history collections (Tse, Cipera, and Leckie 2011;Ford and Druzik 2013), Alaskan native artefacts (del Hoyo-Meléndez and Mecklenburg 2010), textile dyes (del Hoyo-Meléndez and Mecklenburg 2012), and Japanese wood block prints (Connors et al. 2005). It is also used for research (Pearlstein and Keene 2010;del Hoyo-Meléndez and Mecklenburg 2011;Beltran and Druzik 2012;Ford 2014;Lowe et al. 2014;Lerwill et al. 2015aLerwill et al. , 2015bLerwill et al. , 2015cPesme et al. 2016;Ford and Smith 2017), to complement other analytical techniques (Columbia et al. 2013;del Hoyo-Melendez et al. 2016;Troalen et al. 2016), and for risk assessment (Pesme 2016). ...
Birch bark is commonly found in indigenous collections in Canadian museums. It is empirically known that light can cause the cambium side of birch bark to change colour. The purpose of this research is to better assess the light sensitivities of various colours of birch barks, and the manner, degree, and rate of colour change during light exposure. Six barks with different colours were used: beige, yellow, orange, orange-brown, red, and brown. Samples were exposed to daylight through a north-facing window (window), LED light from an enclosed chamber (LED), and the Newport-Oriel microfade tester (MFT). Window and MFT samples received a total light dose of approximately 25 Mlux-hours, and LED samples, 182 Mlux-hours. Colour monitoring of the samples showed that almost all barks initially darkened and then faded. Daylight through window caused the most rapid and extensive darkening and fading. Bluewool (BW) ratings for window samples were the lowest (most light sensitive). The MFT and LED samples showed a similar degree of colour change, with the same dose, despite the difference in intensity. Ratings of MFT samples are within one BW step difference compared to LED samples. The rate and extent of initial darkening depended on the colour of the bark; the middle range orange-toned barks showed the most rapid and extensive darkening followed by fading.
... This was perhaps the first concerted effort to investigate the effect of environmental conditions on color change. Since then there have been numerous investigations on the instability of colorants tempered in aqueous binding media and their response to light and oxidants [15,16]. The red colors based on cochineal, that is carminic acid (CA), 7-d-glucopyranosyl-3,5,6,8-tetra-hydroxy-1-methyl-9,10-dioxo-anthracene-2-carboxylic acid (Fig. 1), a water-soluble extract from the insect Dactylopius coccus [17,18] are among those that are highly light sensitive. ...
Background
Color change in artworks has been commented on for centuries. Fading of watercolor pigments is a notable alteration. Pigments based on carminic acid are among those particularly prone to color loss, but the mechanism and factors are not well understood.
Results
We painted out three pigments prepared from the aqueous extract of carminic acid (CA) from Dactylopius coccus: the uncomplexed, and aluminium- and tin-complexed lakes. These were applied in a 2% gum Arabic solution to papers that were acidic, neutral or alkaline pH and exposed to accelerated light aging in a weatherometer. The comparative rate of fading was dependent on the complexation and on the pH of the substrate. On alkaline paper, the Al complex was least light stable, on neutral paper the three colorants responded similarly, and on acidic paper the tin complex was the least light stable. This is discussed in light of the published information on reactions and mechanism of color loss of CA.Graphical abstractCochineal-based pigments fade on exposure to light. In watercolor paints, the rate depends not only on the complexation of the ligand but also the pH of the paper substrate
... The design for the storage case was developed through consideration of related work from the Getty Conservation Institute (GCI) (Maekawa 1999;Beltran, Druzik and Maekawa 2012), Tate (Lerwill, et al 2015), and the National Institute of Standards and Technology (NIST) (National Bureau of Standards 1951; Robinson 2011) in the U.S. This included developments in low-oxygen case design, and also materials testing to determine the benefits and risks of displaying objects under such an environment. ...
Library and Archives Canada (LAC) holds the two original
copies of the Proclamation of the Constitution Act, 1982 in
the collection. One was signed outdoors and exposed to water
droplets, and subsequently became known as the ‘Rain Drop’
copy. The second was signed indoors; however, it later suffered
intentional damage from an activist in 1983. This copy
is described as the ‘Red Paint’ or ‘Red Stain’ copy. Microfade
testing conducted in 2011 by the Canadian Conservation
Institute (CCI), concluded that the signature inks used on
both copies are highly light sensitive. This information,
coupled with an increasing demand for the long-term display
and loan of the objects, compelled LAC to collaborate
with CCI on the design of a pair of custom storage cases. The
enclosures were specifically developed with the capability of
maintaining low oxygen conditions for the duration of a typical
loan, since the technique has shown promise for slowing
the fading rate of many light-sensitive colourants.
The broader project included several sub-components:
design and construction of the sealed inner display case (or
storage case); design of a document mounting system suitable
for display and transportation; and procurement of a
specialized outer case that addressed additional functional
requirements. These elements are described in the context
of a loan that prompted rapid completion of the work. The
results of preliminary lightfastness testing of fountain pen
inks are also presented.
... Photochemical damage is induced by the absorption of photons followed by structural changes in the absorbing molecule, its decomposition, or its subsequent reaction with surrounding species (as e.g. oxygen) (Arney, Jacobs, and Newman 1979;Beltran, Druzik, and Maekawa 2012;Lerwill et al. 2015a) . It is commonly assumed that for moderate values of the irradiance the reciprocity principle is observable, which means that the degree of light induced damage depends on the amount of radiation absorbed rather than the absorption rate (Bunsen-Roscoe-Law) (Bunsen and Roscoe 1859). ...
Historical objects in exhibitions can be subject to light induced damages resulting in a shift of color and brightness. Besides certain ambient influences the main factor governing these effects is the spectral irradiance applied to the surface. As the photochemical efficiency of electromagnetic radiation depends on its wavelength it is desirable to know the effect of individual spectral components in order to estimate the damage potential of a certain light source. In this work the modifications of the reflectance spectra of 40 dyes and pigments relevant in historical book illumination resulting from irradiation by eight narrow band LED light sources are presented. The LED wavelengths cover the visible part of the electromagnetic spectrum. Based on the measured reflectance spectra, color values are calculated and their evolution is studied as a function of the amount of radiation applied.
... Beside the influence of light, the action of hypoxia/ anoxia on Prussian blue is also of interest for works of art, because anoxic frames are often used to prevent the degradation of paper-based works [12]. The literature http://www.heritagesciencejournal.com/content/2/1/26 devoted to anoxic fading of Prussian blue is significant [3][4][5]7,10,13], and highlighted the sensitivity of the pigment, especially in paper artworks and dyed textiles. ...
Although Prussian blue is a popular pigment, its stability has been questioned since its discovery in 1704. Its stability upon exposure to light and anoxia remains difficult to apprehend. The present paper focuses on the relative influences of light, anoxia and type of substrate on the discoloration of Prussian blue dyed textiles. Spectrophotometry and X-ray absorption spectroscopy measurements of samples artificially aged by light in air or anoxia show that both the extent of the reduction process at the origin of Prussian blue discoloration and the aging of the textile substrate are linked and strongly differ with the environment. The complex inter-relationship existing between Prussian blue discoloration and textile degradation and the final impact it may have on the conservation of the entire system is discussed.
Understanding the chemistry of dyes and pigments found in cultural heritage objects and their permanence is central for their preservation. Heritage science research has generally focused on either identification of materials present on actual objects or accelerated and natural ageing of mock‐up samples prepared using historically accurate methods to simulate the materiality of cultural heritage objects. A more recent strategy is the integration of these two research areas, which provides a holistic approach to assess both the chemical composition and stability of materials. Over the last 30 years, microfading testing (MFT) has notably contributed to understanding materials' responsiveness to light, minimising damage to objects from museum lighting and revealing insights into molecular structures of dyes and pigments, when employed in conjunction with other techniques. By combining MFT with diverse analytical methods, including imaging, spectroscopy, microscopy and chromatography, a more comprehensive approach is achieved. This joined‐up strategy contributes to improved decision‐making processes in the conservation and preservation of cultural heritage objects.
Photo-oxidation has been identified as a main cause of the light-induced color and brightness changes to which historical objects in exhibitions may be subject. Therefore, a possible approach to reduce the risk of light damage is the reduction of the oxygen content in the atmosphere surrounding these objects. In order to estimate the efficiency of this approach, this work presents a comparison of the light induced changes in the reflectance spectra of a series of 30 historical colorants kept in normal ambient air with those observed in a second series stored in nitrogen. Several of them have not been studied in anoxia yet. Chemically inert binder and substrate were used for sample preparation in order to minimize their influence on photochemical processes. In contrast to previous studies on radiative damage in anoxia, the samples were irradiated by various narrow band LED light sources covering the visible part of the electromagnetic spectrum. It becomes obvious that while a few colorants exhibit no or only minor effects due to the reduced oxygen concentration the majority benefitted significantly from this measure. Only four metal-containing pigments suffered increased damage in the nitrogen atmosphere, while three showed a complex behavior and could not be assigned to one of these groups.
Light emitting diodes (LEDs) are steadily finding application in an increasing number of museums and heritage institutions, providing energy-efficient solutions for collections display. Although there is a business case to be made for moving toward LED lighting, the safe display of objects must also be ensured. Identifying vulnerable pigments and paints ensures that future preservation strategies will be put in place, avoiding acerbation of damage and reducing the need for conservation. In the first part of our research we investigate color shift and molecular alterations in three yellow paints, namely, lead chromate sulfate, arsenic sulfide, and cadmium sulfide in linseed oil and gum arabic binders. Following an artificial aging regime, color shift was evaluated using colorimetry and molecular alterations were monitored using attenuated total reflectance–Fourier transform infrared spectroscopy coupled with multivariate analysis. Up to 80 Mlux h the lead chromate samples in linseed oil displayed equivalent color shifts approximating 10 ∆E00 on exposure to the three artificial aging regimes. Color shift has been attributed to the formation of lead oxides evidenced by the appearance of a mid-infrared spectral band at 470 cm⁻¹ assigned to PbO2. Above 80 Mlux h the formation of lead oxides was exacerbated by exposure to one particular LED. Arsenic sulfide in linseed oil displayed color shifts intensified by both types of LED. Above 40 Mlux h there was a discernible color shift in all samples, with the two LEDs displaying ∆E00 values two times higher than those displayed by the tungsten halogen samples. The alterations have been attributed to the formation of As2O3, which is known to form in the presence of wavelengths shorter than 428 nm. Cadmium sulfides in both linseed oil and gum arabic paints did not display discernible color shifts or the presence of degradation products.
The lightfastness of approximately 100 randomly selected red, black and blue inks was surveyed using the microfade technique. The inks’ responses were recorded at 55% and at 1% relative humidity (RH) in air, and in a low oxygen environment (<10 ppm O2) at 55% RH. Their light sensitivity in air was highly unpredictable, ranging from the detection limit of the technique to several times greater than the most fugitive ISO Blue Wool Fading Standard (BW1). With very few exceptions, the response of blue and black inks was markedly suppressed in anoxia, and the opposite was true of a significant proportion of red inks tested. The correlation between RH and light-sensitivity in air was weak, with highly variable responses in both directions. The results show that it is not possible to make useful display (light exposure) recommendations for ballpoint pen inks without prior fade-testing.
This chapter is dedicated to the application of selected spectroscopic techniques to investigations on cultural heritage objects. The rapid technical advancement of Raman instrumentation, observed in the recent years, positioned this spectroscopy as an outmost tool in this field. The use of Raman spectroscopy in the analysis of chemical composition is presented for several classes of heritage materials: manuscripts, painting, ceramics, minerals, and amber. In Sect. 16.3, Vis fiber optic reflectance spectroscopy is presented as a tool allowing one to obtain information important for selecting proper preventive measures, in this case, exhibition policies safeguarding artifacts against photodegradation. The technique discussed here—the microfade testing (MFT)—allows monitoring color changes as induced by the action of light on a selected spot on the artifact in real time, thus giving the most direct, empirical clues to a possible future alteration of the objects’ appearance when it is exposed to light on a museum wall.
The impact of the spectral composition of light on the discoloration of paint pigments has been investigated for the case of lead chromate sulfate, an unstable yellow pigment used by Vincent van Gogh and other painters. With LEDification, museum lighting is moving from using halogen to LED lamps. LED light sources have a significantly different spectral composition than halogen lamps. To understand the impact of these differences on pigment stability, the wavelength dependence of pigment discoloration was determined. Contrary to the expectation that lower wavelength photons induce more damage than higher wavelength ones, UV (394 nm), blue, and cyan light all lead to similar levels of discoloration of a pigment for the same level of radiant power. By understanding this wavelength dependence, it becomes possible to create white light LED lamps with a spectral composition tuned to minimize the degradation effect. An existing LED solution with a modified emission indeed resulted in 30% less color change in the experiment than halogen. Furthermore, a method is proposed to optimize the LED spectra by tuning to the properties of each specific artifact. Simulations show that this can reduce the damage of the light source by 45% in specific cases.
Two investigations of the validity of microfading spectroscopy to predict the fading behavior of a diversity of colorants at lower light levels is discussed. The specific research question being: what is the probability that a particular sample being tested with micro-fading will alter significantly differently from the same luxhours light exposure at ambient light intensities? In one experiment two ISO Blue Wool Standards and 15 dyed papers were tested. Accelerated light aging at four illuminance levels stepping from 250 lux to one tenth of the microfading irradiance of 12.5 Mlux was conducted over different time periods using either standard fadometer lightfastness testing apparatus or a microfadometer. Samples received similar lux-hours exposure. In a second experiment a 2.2 Mlux illuminance from a microfadometer was compared to that of a QUV Weatherometer light aging chamber (with UV filtration). Ten different dyes were each faded for 10 minutes using the microfadometer and then for 21 hours using a QUV Weatherometer (with UV filtration). Samples again received the same lux-hours exposure. Results from both experiments illustrate a positive correlation between the compared light sensitivity testing methods, leading to the conclusion that fugitive colorants can be reliably highlighted by the microfading technique. In both experiments a lower value of induced color difference was observed when using microfading compared to standard lightfastness testing apparatus (light box aging) indicating that the quantative prediction of color change from real illumination in lower illuminance conditions is not secure. A short discussion of the origins of error in the technique follows.
Limiting light-induced colour change of displayed objects to an acceptable degree is an important but difficult task for conservators, who are required to make exposure decisions which have fundamental consequences for access and display, usually without adequate rate data. The NMA’s early experience with an accelerated fading technique known as microfading, which uniquely allows the relative rates of colour change of actual museum objects to be estimated, is described. The technique is rapid, essentially non-destructive and highly cost-effective, allowing the museum to identify and concentrate its resources on protecting the most vulnerable objects, rather than applying blanket rules to very broad classes of colourants.
A wide-ranging sample set consisting of dry pigments, dyed textiles, organic and aniline-based dyes, gouaches and watercolors, fluorescent inks, and natural history specimens was exposed to light in air (20.9% oxygen) and near-anoxic environments. After a light dosage of approximately 17.5 Mlux-hours under controlled temperature and humidity conditions, 113 of 125 samples (90% of the sample set) were shown to exhibit less color change in a low-oxygen environment compared with its behavior in air. Thirty-nine percent of this subset displayed color change in anoxia that was between two and four times lower than that observed in air, whereas 47% showed color change in anoxia reduced by a factor of four or more. In contrast, six samples exhibited greater color change in anoxia than in air – these samples included Prussian blue watercolor (three samples), Antwerp blue watercolor, Verdigris dry pigment, and Fluorescent Yellow Winsor & Newton Gouache. Although the results from this small sample subset may cause concern when considering the use of anoxia in the conservation of cultural heritage, particularly for colorant systems whose behavior in anoxia has not yet been identified, this study demonstrates the overwhelming benefits of anoxic light exposure for the vast majority of samples investigated here.
Information on the light-fastness of natural dyes is reviewed. New tests on the fastness of several dyes in fluorescent lamp light are reported. Nearly all natural dyes have a light-fastness below BS grade 5. Most have a fastness below 4. Nearly all natural dyes will fade badly during an exposure to 50 million lux hours of artificial light, or to a much smaller dose of daylight. In many museum displays serious fading of most dyes would occur in less than fifty years. There is no very effective way of reducing the rate of fading. Ultraviolet absorbers over light sources give a worthwhile increase in light-fastness to most, but not all, dyes. Low relative humidity reduces fading. Display in cases filled with an 'inert' gas benefits most dyes but accelerates the fading of some pigments used on fabrics. Valuable textiles whose dyes have a light-fastness below 6 should not be permanently displayed.
Book description: The Pigment Compendium Dictionary is a comprehensive information source for scientists, art historians, conservators and forensic specialists. Drawn together from extensive analystical research into the physical and chemical properties of pigments, this essential reference to pigment names and synonyms describes the inter-relationship of different names and terms. The Dictionary covers the field worldwide from pre-history to the present day, from rock art to interior decoration, from ethnography to contemporary art. Drawing on hundreds of hard-to-obtain documentary sources as well as modern scientific data each term is discussed in detail, giving both its context and composition.
The design and experimental method for the use of a novel instrument for lightfastness measurements on an artwork is presented. The new micro-fading spectrometer design offers increased structural stability (which enables portability) and increased versatility over the previous, published design, broadening the scope of locations at which data can be acquired. This reduces the need for art handling or transportation in order to gain evidence-based risk assessments for the display of light-sensitive artworks. The instrument focuses a stabilized high powered xenon lamp to a spot 0.25 mm diameter (FWHM) while simultaneously monitoring colour and spectral change. This makes it possible to identify pigments and determine the lightfastness of materials effectively and non-destructively. With 2.59 mW or 0.82 lumen (1.7·107 lux for a 0.25 mm focused spot) the instrument is capable of fading Blue Wool 1 to a measured 11 ΔEab value (using CIE standard illuminant D65) in 15 min. The temperature increase created by focused radiation was measured to be 3 to 4 °C above room temperature. The system was stable within 0.12 ΔEab over 1 h and 0.31 ΔEab over 7 h. A safety evaluation of the technique is discussed whichconcludes that some caution should be employed when fading smooth, uniform areas of artworks. The instrument can also incorporate a linear variable filter. This enables the researcher to identify the active wavebands that cause certain degradation reactions and determine the degree of wavelength dependence of fading. Some preliminary results of fading experiments on Prussian blue samples from the studio materials of J. M. W Turner (1755-1851) are presented.
The paper deals the planning of a preventive conservation strategy for the rock art (paintings and engravings) of the Cueva de Altamira, as a natural ecosystem which has survived for more than 14,000 years. The first stages of the project include design and implementing a lighting system and a data acquisition system for the continuous monitoring of different environmental factors. The paper shows the technical criteria for the design of this equipment.
Reduced-oxygen display and storage, through the limitation of oxidative processes, can enhance the
preservation of works on paper. By limiting photo-oxidative processes, access to objects can be increased,
allowing their display at higher light levels and/or for longer periods. Published research indicates that most
artists’ materials will either benefit from or suffer no detrimental effect from reduced-oxygen environments.
However, some colourants have been found to undergo accelerated change in the absence of oxygen.
Therefore, evaluation of benefits to heritage objects prior to reduced-oxygen treatment is required.
The Anoxic Frames Project at Tate, of which this Thesis is an outcome, aimed to develop reduced-oxygen
framing solutions, test their efficacy, identify materials that undergo accelerated change in a reducedoxygen
environment and develop methods to identify candidate objects for anoxic storage. The scope of my
research at Tate and for this Thesis was limited to 19th-century watercolour drawings, with a focus on J.M.W.
Turner. My research contributed to several publications, conference papers, posters, reproduction of a 19th-
century paper, a prototype reaction cell and was, in part, patented.
This Thesis presents: a literature review of both the behaviour of artists’ materials in zero oxygen (anoxia)
and of analytical methods; a technical study leading to the reproduction of a paper used by Turner;
analytical studies of the photo-reactivity of madder lakes and Prussian blues; the design and testing of a
prototype reaction cell for operando spectroscopy studies of heritage materials; an outline of the field of
heritage degradomics; the application of heritage degradomics with advanced chemometric methods to
evaluate the headspace profiles of watercolours aged in both anoxia and room atmosphere. The Thesis
concludes with an evaluation of reduced-oxygen treatment, and a proposal of how heritage institutions can
both select objects suitable for reduced-oxygen storage and display and implement low-cost reducedoxygen
cassettes in their display practice.
An experiment was conducted to determine the effects of fumigation by anoxia on textiles dyed with Prussian blue. The experiment reproduced methods used in real fumigation treatments in museums. The chemistry of Prussian blue dye suggested that it might fade by reduction in anoxic conditions, but that this fading might spontaneously reverse on re-exposure to air. Victorian dye recipes were adapted to make two main types of Prussian blue dye for the experiment. The experiment used tristimulus colour measurements and Fourier transform infrared spectrometry to assess colour change in the dye after a three-week fumigation using Ageless®. Statistical analysis showed that anoxic fumigation caused significant fading and chemical change in Prussian blue. The effects of textile type and dye type were also studied. Partial reversal of fading was noted; after two weeks' re-exposure to air some samples had fully recovered, while others still showed some colour change. It is recommended that anoxic fumigation should not be used on historic textiles dyed with Prussian blue, since deteriorated dye may not recover from fading as well as the modern samples tested.
The fading rate curves of selected natural dyes were constructed from color difference measurements made using a tristimulus colorimeter. Examination of the curves showed that most natural dyes fade rapidly initially followed by a slower rate of fading. Only the most lightfast natural dyes fade at a constant rate over time. The implications of these findings for museum textiles are discussed. /// On a établi les courbes de vitesse de fadissement de quelques teintures naturelles, à partir des mesures des différences colorées par un colorimètre à trois stimuli. L'examen des courbes a montré que les teintures les plus naturelles fadissaient d'abord rapidement puis à une vitesse plus lente. Seules les teintures naturelles les plus stables à la lumière fadissent à vitesse constante. On discute les implications de ces résultats sur la conservation des textiles. /// Die Verblassungsgeschwindigkeitskurven ausgewählter natürlicher Farbstoffe wurden aus Farbunterschiedsmessungen erstellt, die unter Benutzung eines trichromatischen Kolorimeters durchgeführt wurden. Die Untersuchung der Kurven zeigte, daß die meisten natürlichen Farbstoffe anfangs schnell verblassen und eine langsamere Verblassungsgeschwindigkeit folgt. Nur die lichtbeständigsten natürlichen Farbstoffe verblassen im Verlaufe der Zeit mit einer konstanten Geschwindigkeit. Die Implikationen dieser Ermittlungen für Museumstextilien werden erörtert.
In our laboratory we have developed a micro-fading tester, a device capable of performing non-destructive accelerated fading tests on submillimetre areas of coloured materials. The original purpose of these micro-fading tests was to provide rapid ‘screening’ of the colourants present on artifacts and to identify those having extreme sensitivity to visible region light exposure. Recent field tests have made it clear that another important application of these test results is the prediction of colour changes that would result from light exposure in particular exhibition conditions and schedules. In this paper we explore the accuracy of the micro-fading tests, and the factors that affect that accuracy. An overall judgment of the use of micro-fading test results and the prospects for future refinement of the tests are discussed.
Analyses of pigments from palettes used by J.M.W. Turner (active c.1792–c.1850) by means of microscopy, microchemical analysis, thin-layer chromatography, energy-dispersive X-ray analysis, X-ray diffraction and Fourier transform infrared spectroscopy are given. The occurrence of pigments in Turner's dated oil paintings and watercolours is also given, arranged by five-year periods. These findings are discussed in the context of published analyses of pigments from the first half of the nineteenth century. Turner used cobalt blue, emerald green, viridian, orange vermilion, barium chromate, chrome yellow, chrome orange and chrome scarlet within a few years of their known dates of discovery. It has become clear that Turner was using, or at least experimenting with, practically all the pigments known to be available at that time. In a few cases, in the light of these results, ideas on the availability of pigments to English artists have been revised backwards to the first known date of manufacture. Turner also possessed and used a wide range of red and yellow organic pigments, but few organic greens. The dyestuff extracted from Rubia tinctorum L. madder on an aluminiumcontaining substrate can be distinguished from the same madder on different substrates by its strong pink fluorescence in both ultraviolet and green light. The other red organic pigments (a second madder, brasilwood and cochineal dyestuffs on a range of substrates containing aluminium, copper, iron, aluminium/copper and clays) show negligible fluorescence. The red organic pigments were used in oil medium as well as watercolour, the yellows only in watercolour medium.
The use of Prussian blue in nineteenth-century Japan has been extensively researched, particularly in relation to the ‘blue revolution’ in ukiyo-e prints but its use by Chinese artists has not received the same degree of attention. A commodity traded by the East India Company, this pigment was used to ‘improve’ the colour of tea, but in or about 1825 the trade abruptly ceased. It now seems fairly clear that the cessation of the Prussian blue trade coincided with the setting up of a Prussian blue factory at the northern gate of Canton, and that knowledge of the industrial process was possibly acquired covertly from a London manufacturer. The pigment has been identified chemically among paint fragments collected during the dis-binding of an album of Chinese botanical watercolours sent from Canton to the Horticultural Society of London by tea inspector John Reeves between 1817 and 1830. This finding suggests that conservators should not exclude the possibility of finding Prussian blue on Chinese work dating from at least the early part of the nineteenth century.
A new approach to identifying artifacts sensitive to visible light exposure, based on the direct measurement of the lightfastness of materials that compose the object, is described. An instrument has been constructed that is capable of identifying fugitive materials (more light sensitive than Blue Wool #2) rapidly and essentially nondestructively. Accelerated light-fading tests on tiny (0.4 mm diameter) areas of an object are done while simultaneously monitoring the color change produced in the test area. The lightfastness determined in such microfading tests has been found to compare well with that measured in more conventional accelerated lightaging tests. The risks of damage to the artifacts from these microfading tests have been examined. By terminating the fading test when a small but definite color change has been produced, the risk of disfiguring the object by creating a visible bleached spot is judged to be very small. Exposure to the light intensities used in the microfading tester can heat test areas to as high as 50°C, so that low-melting materials such as waxes should be considered at risk of some degree of melting damage. For most art materials that are more heat tolerant, however, this technique holds great promise as a tool for recognizing very light-sensitive materials and for 'predicting the consequences of exhibition under particular lighting or atmospheric conditions.
The feasibility of using an oxygen-free environment to retard the rate of fading of colorants has been explored. The factors by which the life expectancy of a variety of colorants would be multiplied in such an environment were determined by accelerated fading experiments. In general, the life expectancy of most colorants can be increased by such techniques, but a complete halt of the fading process has not been generally observed. In addition, some colorants were found to fade more quickly in an oxygen-free environment. However, it has also been found that at least 90% of the beneficial influence of an oxygen-free environment can be realized with as much as 0.2% oxygen (1% air) remaining in the environment of the colorant. Such an environment might be achieved and maintained at relatively little expense.
C'est en 1888 que le Dr Russell et le Capitaine Abney publièrent les résultats d'une série d'expériences très poussées, sur l'influence de la lumière sur les aquarelles. Ils ont exposé des spécimens sur papier Whatman aux rayons solaires et à la lumière diurne, équivalant à au moins 480 ans d'exposition à la lumière du jour dans les galeries de peinture (calcul par les auteurs). Dans la liste suivante figurent les résultats par ordre de stabilité, en commençant par les pigments les plus instables: Carmin fin, laque cramoisie, garance pourpre, laque écarlate, gris de Payne, jaune de Naples, vert olive, indigo, garance brune, gomme-gutte, brun Van Dyck, stil-de-grain, jaune indien, jaune de cadmium, bleu de Leitch, carmin violet, carmin pourpre, sépia, auréolin, garance rose, bleu permanent, bleu d'Anvers, laque de garance, vermillon, vert Véronèse, terre d'ombre brûlée. Les pigments qui ne montrent aucun changement après exposition sont les suivants: ocre jaune, rouge indien, rouge de Venise, terre de Sienne brûlée, jaune de chrome, outremer jaune, terre de Sienne naturelle, terre verte naturelle, oxyde de chrome, bleu de Prusse, bleu de cobalt, bleu d'outremer, cendre d'outremer. Après d'autres expositions à l'air sec, à l'air humide, à l'hydrogène, sous vide, sous verres colorés, etc., Russell et Abney sont arrivés aux conclusions suivantes, choisies parmi plusieurs: la présence d'humidité et d'oxygène est, en général, essentielle pour que s'effectue une altération. Les parties composantes de lumière blanche des bleus et violets produisent les altérations les plus importantes. Le compte rendu se termine en en esquissant quelquesunes des conséquences.
It is frequently assumed that sensitive museum materials follow the reciprocity principle of light exposures. Thus, equivalent exposure doses obtained by using either high-illuminance levels for short periods of time or lower illumination for longer exhibition periods are believed to cause similar degrees of damage to an object. Microfading spectrometry permitted the investigation of this phenomenon by evaluation of light-induced changes in a series of samples. The effects of equivalent exposure doses on materials such as Blue Wool 1, LightCheck Ultra, and various dyed silks from a reference collection were compared. The results indicate that reciprocity is obeyed by the most stable colorants, while materials with lower stability to light may experience deviations that are proportional to the intensity of illumination. This study confirms that reciprocity failure is associated with the use of high-intensity lamps during accelerated-aging trials. Therefore only those tests conducted at low-illumination intensity ranges where reciprocity holds should be employed when one estimates the extent of damage occurring in a museum environment.
Prussian blue was advertised in Berlin, in 1710, as an opaque pigment of excellent covering power, and was in use (on a decorative element) in Berlin by 1712, and in England before 1721. The modern pigment is lightfast, except when mixed with an abundance of white. Fading of Prussian blue used for skies has been observed in Gainsborough and other eighteenth-century artists, and cross sections may show a grey appearance in consequence. The earliest product was made from dried blood, and had a poor reputation for lightfastness. The chemistry of early and modern Prussian blues is discussed. Water solubility of the pigment increases with increasing potassium content, and so has a tendency to fade, though the manufacturing process also affects lightfastness. English-made Prussian blue was said by several non-English authors to be the best, as regards permanence and brilliance, in the earlier nineteenth century.
Prussian blue was the first totally modern synthetic pigment made as a product of a chemical reaction. The production of Prussian blue is described as difficult to control and may result in changes of colour in the final product. The chemistry of manufacture and structure of Prussian blue is discussed. Prussian blue is characterized as being inexpensive and intensely coloured and as having a high tinting strength. The presence of white pigments as an extender contributes to the permanence of the coloured paint film. Samples of Prussian blue paint films from 18th- and 19th-century paint films were studied. Samples from paintings are compared to samples prepared in the laboratory. Differences between these samples are discussed. Experimental procedures studied colour change in samples of Prussian blue- and lead white-containing paint films in cold-pressed linseed oil and watercolour media exposed to light. Reversible colour change and redox reactions are addressed. The difference in paint media did not have an effect on the degree of colour change. It is noted that the presence of alumina as an extender in paint films increased the rate of fading when paint films were exposed to light. The mixtures of Prussian blue and white pigment had an increased effect on the colour change of the paint film when compared to paint films pigmented with Prussian blue alone.
Tate is undertaking a major research project to assess the effects of anoxic storage on paper-based works of art. The outcomes will include: the design of a safe, affordable anoxic framing system suitable for both storage and display, capable of being incorporated into historic frames; guidelines on materials which would be harmed by anoxia and information on their recognition and behaviour. Such framing would provide safer access to paper-based works of art. This paper reviews the following materials found in paper-based works of art that are susceptible to oxidation and which could therefore benefit from anoxia: traditional colorants; modern pigments; graphic media; printing, copying or photographic processes; and oil or alkyd media. Materials, predominantly colorants, which may be susceptible to reducing reactions that proceed in the absence of oxygen, are identified for later study into their behaviour and their non-destructive identification on paper-based works of art.
Notes eighteenth-century views on the impermanence of cochineal and brazilwood red lakes. Describes faded cochineal identified in paintings by Reynolds and Gainsborough, and faded lac lake in a Jacopo di Cione. Loss of organic reds is noticeable through loss of modelling in red and purple paints, while loss of organic yellows is apparent in 'blue' foliage or fruit, particularly in Dutch seventeenth-century paintings and those of Greuze. Previous studies of the lightfastness of organic pigments are noted: most included modern industrial products, not traditional pigments, even when carried out in the later nineteenth century. In a very comprehensive study, pigment samples were prepared by the authors by dyeing wool with cochineal, kermes, lac, or madder and then extracting the dye with alkali and precipitating it onto alum. Brazilwood, modern alizarin crimson and yellows extracted from buckthorn, quercitron and weld were also used. Samples of each in gum arabic, egg tempera, or linseed oil, some mixed with lead white 1:1 to 1:3, were painted out, aged under fluorescent lamps, and color measurements were made. (Details are given). Anthraquinones such as alizarin and madder are the most stable for a given substrate, and tin-based substrates were the least stable. Weld was the least fugitive yellow. Yellow dyes and carmine on an aluminum-containing substrate were more stable than on other substrates. Thick or heavily-pigmented layers faded less than thin ones. Lead white samples showed altered tonal gradation after light aging.
The use of inert gases for displaying sensitive objects and for the treatment of artifacts infected with bio-deteriorating agents is a current practice in many cultural institutions around the world. However, some artifacts may also experience color changes as a result of exposure to light in these reducing environments. Therefore, it becomes essential to evaluate the light stability of an object under anoxic conditions prior to its exhibition. This study dealt with the development of a procedure based on micro-fading spectroscopy to determine the light fastness of materials when exposed to an argon atmosphere. The efficacy of this method has been tested using turmeric/silk and Prussian blue/silk systems. Evaluation of color changes in real time have demonstrated that the approach provides an efficient way of detecting any potential variation occurring as a result of long-term anoxic display in a museum environment.
The rates of oxidation and of reduction in aqueous solution, and of fading in films of a typical protein (gelatin) and a typical non‐protein (methylethylcellulose), have been determined for several series of dyes of different chemical classes. The general conclusion reached is that the photodegradation of a dye may follow either of the alternative mechanisms of oxidation or reduction, but normally oxidation occurs more readily on all non‐proteins and reduction on proteins. In photochemical oxidation of dyes on non‐proteins the substrate does not necessarily take part directly, but in reduction on proteins some constituent of the protein itself appears to act as the reducing agent. The histidine side‐chains are probably the active constituent.
The conclusions in some instances have been confirmed by examination of spectral absorption curves of oxidation, reduction, and fading products of certain dyes.
The photo degradation of watercolour drawings prepared with madder lake pigments on gelatine-sized paper was studied by chemiluminometry, viscometry, and colorimetry. A method of recto irradiation and verso measurement was developed to overcome absorption of the emitted photons by the paint layer. A complex relationship between paper substrate, applied chromophores and associated transition metals was observed with strong correlations between the presence of transition metals associated with the madder lakes and the degradation of the paper substrate and the applied paint layer as well as evidence of pro-oxidative activity by the chromophores in the applied paint layers. The pro-oxidant behaviour appears to be dependent on the type of transition metal present. This is the first in-depth research into the photodegradation of madder lake-based watercolours which attempts to understand the chemistry of the processes.
The Continuing Development of a Practical Lighting Policy for Works of Art on Paper and Other Object Types at the Victoria and ALvert Museum
- J Ashley-Smith
- A Derbyshire
- B Pretzel
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Paper and Other Object Types at the Victoria and ALvert
Museum. In: R. Vontobel, ed. ICOM-CC 13th Triennial
Meeting Rio de Janeiro Preprints. London: James and James,
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Reconstructing 19th-century British Watercolour Paint
- C Caspers
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Paint. Masters Thesis, Stichting Restauratie Atelier Limburg
(SRAL) and University of Amsterdam, The Netherlands.
Comparison of Five Microfading Tester (MFT) Designs. In: American Institute of Conservation 38th Annual Meeting. Milwaukee, WI: The Textile Specialty Group Postprints
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Lighting Guidelines and the Lightfastness of Australian Indigenous Objects at the National Museum of Australia
- B Ford
- N Smith
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Influence of Gas Pressure on the Bleaching of Dyes in the Visible Spectrum
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Interim Reports on Artificial Ageing of Yarns to the ICOM Conservation Committee at the meeting's final report
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The Identification of Indigo and Prussian Blue on Japanese Edo-period Paintings
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Blue on Japanese Edo-period Paintings. In: E.W. Fitzhugh, ed.
Studies using Scientific Methods: Pigments in Later Japanese
Paintings. Washington, D.C.: Freer Gallery of Art, Freer
Gallery of Art Occasional Papers New Series, 1: 63-87.
Micro-fading Spectrometry: An Investigation into the Display of Traditional Watercolour Pigments in Anoxia
- A Lerwill
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Report on the Action of Light on Watercolours to the Science and Art Department of the Committee of Council on Education. London: HMSO
- W Russell
- W De Abney
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Turner's Painting Techniques
- J H Townsend
Townsend, J.H. 2007. Turner's Painting Techniques. 4th ed.
reprinted. London: Tate Publishing.
Who's Not Afraid of Displaying Kurt Schwitters' Collages? A Microfadometry Study to Determine the Sensitivity to Light of Five Examples
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- P Townshend
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Cyanotype: the History, Science and Art of Photographic Printing in Prussian Blue. London: Science Museum
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