Large-scale assessment of light-induced color change in air and anoxic environments

Abstract

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.     

Can LEDs help with art conservation? – Impact of different light spectra on paint pigment degradation

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.     

The presence of antimony in some grey colours of three paintings by Correggio

Abstract

This paper describes analyses that were performed on three canvas paintings by Correggio, the‘Danae’, the‘Compianto suI Cristo Morto’ and the‘Martirio di Quattro Santi’, with special regard to the grey colours. Non-destructive XRF measurements showed that the elemental composition of these colours included non-negligible amounts of antimony, and that its abundance was related to the darkness of the colour. Optical microscope, SEM and EPMA analyses, carried out on a single sample taken from the‘Danae’, confirmed that antimony was associated with the grey layers of the stratigraphical section and allowed us to hypothesize the presence of stibnite, which is a lead-grey coloured antimony trisulphide.     

Degradation of Emerald green in oil paint and its contribution to the rapid change in colour of the Descente des vaches (1834–1835) painted by Théodore Rousseau

Abstract

Descente des vaches (1836) by Théodore Rousseau in the Mesdag Collection in The Hague is barely readable and its paint layers are in poor condition. The surface of the painting is strongly deformed and cracked, the whole painting has darkened and especially the greens have lost all or most of their colour resulting in brown passages. Large passages of the painting that were painted with multiple thick and medium-rich layers have darkened dramatically. This paper proposes that the degradation of Emerald green (Cu(C₂H₃O₂)₂·3Cu(AsO₂)₂, copperacetoarsenite) – the main green pigment used in this painting – is a significant factor in the cause of the darkening. Electron backscatter images reveal that the Emerald green particles are shown different degrees of degradation: from partially to completely disintegrated. Elemental maps show that arsenic is distributed throughout the paint cross section, with relatively higher concentrations around iron- and aluminium-containing particles, and in the varnish layer. Imaging-Fourier-transform infrared microscopy detects copper soaps in the degraded Emerald green-containing layers. Analytical data from four paint cross sections strongly suggest that Emerald green reacts with free fatty acids derived from the binding medium forming copper soaps and mobile arsenic-based species. Chemical laboratory experiments fully support this hypothesis. Emerald green and palmitic acid in chloroform form copper palmitate and arsenic trioxide (arsenolite, cubic) under room temperature and normal light conditions. The degradation of Emerald green particles in Descente des vaches has resulted in a loss of light-reflecting surfaces and in newly formed compounds in the paint, both contribute to the colour change from green to brown.     

Consolidation of Black-dyed Māori Textile Artefacts: Evaluating the Efficacy of Sodium Alginate

Black-dyed artefacts are found in museums worldwide, many produced using an iron-tannate compound. Deterioration of iron-tannate dyed artefacts is an international preservation issue: in New Zealand the deterioration of paru (iron-tannate) dyed Māori textiles is widespread. This article reports experimental work testing the efficacy of sodium alginate, a consolidant developed for deteriorated paru-dyed muka (fibre from harakeke; Phormium tenax). The colour stability, strength retention, and acidity of paru-dyed muka consolidated with sodium alginate (0.25, 0.5, and 1% w/v in water) was tested pre- and post-artificial light ageing. This study found that sodium alginate had no negative effect on paru-dyed muka and in some cases provided benefit. Interestingly, the colour of paru-dyed muka is substantially more stable in UV-filtered light than previously recognised. Also microfading results were in agreement with visual assessments of colour change at 1 Mlux hour exposure, providing confidence in this relatively new technique to assess colour change.     

Blue Enamel on Sixteenth - and Seventeenth-Century Window Glass

Abstract

It is still unclear why some of the blue enamel on sixteenth- and seventeenth-century stained window glass is flaking off, while enamel layers with other colours are still in relatively good condition. In order to obtain a better understanding of this conservation problem, 31 historical recipes used for the fabrication of blue enamel were compared with results from the chemical analysis of 25 historic samples. The chemical composition and the microstructure of the enamels were analysed in cross-section by means of electron probe microanalysis (EPMA). This study demonstrated that the variation in chemical composition of the samples can be explained by the use of the wide range of recipes existing at that time. Although this study gave an insight into the composition, heterogeneity and use of colouring substances, no clear relation could be found between the parameters analysed and the deterioration rate of the blue enamel paint layer.     

Spread or Sacrifice: Dilemma for Lighting Policies

ABSTRACT

Light sensitive objects will fade on display. Collection managers and curators face the dilemma whether to spread fading over several similar objects or sacrifice one. This paper describes an experiment in which participants were asked how they would want to pass on a collection of seventeenth century hand-coloured maps to coming generations. Results show that while colour changes are hardly visible, both public and professionals do not perceive them as damage and prefer to spread fading. Once fading becomes clearly visible in all maps, the preference shifts to sacrificing one map. The tipping point lies around five just noticeable changes. This information can be used when selecting objects for exhibition. The outcome also implies it would be prudent to assess the degree of fading of much exhibited objects and consider whether and when to choose for a sacrifice strategy.     

Identification of Synthetic Organic Pigments by Characteristic Colour Reactions

Abstract

The purpose of this study was to develop a method for the identification of synthetic organic pigments on the basis of colour reactions with four different chemical reagents: concentrated sulphuric acid, concentrated nitric acid, a mixture of concentrated sulphuric acid and concentrated nitric acid and, finally, a solution of potassium iodate in concentrated sulphuric acid. Colour reactions for a large number of synthetic organic pigments in the form of pure powdered material were recorded. It is shown that the colour reactions observed are in overall agreement with the chemical grouping of pigments (for instance, naphthol AS pigments or quinacridone pigments), i.e., pigments belonging to the same pigment group yield similar colour reactions. This fact is the basis for the construction of flow charts for identification. Tests performed on a number of artists' colours containing pigments in various binding media show that the binding media do not noticeably affect the colour reactions observed, making the flow charts useful for the identification of actual artists' pigments. A fifth chemical reagent, namely a saturated solution of potassium hydroxide in 96% ethanol, was tested and abandoned as a result of its instability, which resulted in severe problems with reproducibility, especially for certain pigment groups, for example the acetoacetarylide pigments.     

Effect of Light on Modern Digital Prints - Photographs and Documents

Abstract

This project examines the lightfastness of prints created with the most commonly used digital technologies (inkjet, color electrophotography, dye sublimation and digital press) along with prints created using traditional technologies (color photography, black-and-white electrophotography and offset lithography). The inclusion of traditional prints provides benchmarks for collection care professionals to better gauge the significance of the results. In this study, prints were subjected to two types of lighting used independently to simulate daylight through window glass and artificial indoor illumination. Five aspects of light damage were assessed: fade in the mid-tone neutral, fade in the darkest neutral tone, paper yellowing, changes in paper gloss and text readability. In general, digital prints were less sensitive to light than traditional prints; but each digital printing technology produced at least one sample that performed worse than its traditional benchmark in at least one of the aspects of light damage studied. Therefore, it is recommended that cultural heritage institutions strive to provide the most benign environment possible, taking display practices currently in use for traditional prints as a minimum starting point for the care of digital prints. Close monitoring for signs of change is also recommended.     

Mechanical strength studies on degraded waterlogged wood treated with sugars

This study aims to measure the mechanical strength of chemically degraded wood samples and compare the values obtained with fresh wood and degraded wood treated with sugars. The mechanical strength of chemically degraded waterlogged wood samples was determined using a three-point bending system to generate load-deflection curves and subsequently calculate the modulus of elasticity and load to failure longitudinally. The values obtained allow us to compare the mechanical properties of white birch wood samples that were air dried after treatment with 60% w/v solutions of sucrose, trehalose, or sucralose. In addition, the same parameters were measured for fresh white birch wood samples and chemically degraded samples that were allowed to air dry without treatment. Fresh white birch was found to have a longitudinal modulus of elasticity of 11.5?GPa whereas this value decreased by 70% when the wood was degraded. Treatment with sugars increased the measured values of modulus of elasticity up to 36.9?GPa, a substantially higher value than for fresh wood. These data indicate that non-reducing sugars could be useful alternatives to polyethylene glycol for the conservation of waterlogged archaeological wood.     

Microfade Testing for Heritage Institutions: A Canadian Experience

ABSTRACT

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.     

Wavelength Dependence of Light Induced Changes in Reflectance Spectra of Selected Dyes and Pigments

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.     

Light damage to selected organic materials in display cases: A study of different light sources

The protection of works of art and cultural assets against light-induced aging is vital when planning exhibitions. Newly developed lighting systems render the selection of suitable light sources more difficult, not least in the context of energy–economical systems. This study accordingly examines different lighting systems (fluorescent tubes, halogen lamps, low-voltage metal halide lamps, and LED lamps) in terms of the damage potential they hold for the materials concerned. The changes in color were evaluated using the CIEDE2000 color-difference formula. This study focuses on selected organic materials and shows that changes in color already occur after only a brief exposure time. The color changes induced by the fluorescent tubes were consistently more intense than those induced by the other light sources. The results obtained with the remaining lamps show that the color changes depend more on the material under investigation than on the source used. The changes determined after a relatively short exposure period (five months) vividly demonstrate that exposing sensitive materials to light for longer terms (as is the case during a permanent exhibition) is most definitely a non-viable option.     

Epoxy resin-consolidated stone: appearance change on aging

Abstract

Dilute solutions of epoxy resins have been used successfully in the past to consolidate deteriorated, porous stone. However, the appearance change (darkening, yellowing) on curing has proved to be a deterrent to the wider use of these materials by conservators. In the study reported here, it is shown that solvent washing to remove surface-deposited resin and exposure to sunlight are effective methods for restoring the original visual appearance of consolidated outdoor stone.     

基于文献计量分析的LED知识图谱及产业化对策

LED照明是当前最具发展前景的高技术领域之一.本文运用文献计量相关分析方法对LED的历史文献进行分析,通过绘制多维尺度分析图谱和核心关键词关联知识图谱,挖掘当前LED的技术成熟度、研究热点和关键技术点等信息,得出LED技术目前主要集中宽带隙材料、发光类型及特性、有机发光和超亮度LED研发上;氮化镓(GaN)、电致发光(electroluminescence)、光致发光(photoluminescence)、白光(White LED)等在整个LED研究中处于中心和控制大多数信息流向的地位.最后,本文通过国别分析判断我国LED产业的实力水平,最终为我国的LED技术产业化发展提供建议.     

'Diasec' and Other Finishing Techniques - Investigation of Accelerated Light Fading

Abstract

A study of the accelerated light fading behavior of face-mounted color photographic materials has shown that alterations on the surface of the materials influence their fading characteristics. With the help of spectral density measurements it became apparent that the application of materials such as silicone rubber, adhesive film and acrylic sheeting, but also laminating films, onto the surface of the prints accelerated the degradation of the colorants, especially the yellow dye, in chromogenic materials. In the case of silver dye bleach materials, however, the opposite effect was observed. The influence of the material combination on the stability of face mounted color photographic prints was demonstrated to vary considerably. In order to better assess the inherent damage potential of the materials themselves, these were examined by means of instrumental analysis and measurements of pollutant gasses. Besides off-gassing compounds such as acetic acid and changes in pH caused by aging of the adhesive, face-mounting with a rigid plastic sheet (acrylic glazing) also affected the respective fading behavior of the various materials that were tested.     

A methodology for evaluating the performance of CISC computer systems under single and two-level cache environments

This paper presents a simulation methodology for evaluating the performance of CISC computers. The method is called Message Flow Technique (MFT). MFT has several advantages over Instruction Flow Technique (IFT) we presented in [1]. The proposed methodology is applied to a single and two-level cache CISC system using 80486 SX as a case study. It was found that with a single-level on-chip cache of size 8KB, the performance of the system is considerably limited by the service time of BIU (Bus Interface Unit). The average service time of BIU, per instruction, was found to be around 1.0135 microseconds for our Modified Gibson Mix (MGM). With a second-level external cache of sizes 16KB, 32KB, 64KB, and 128KB the average performance improvements were found to be 1.4%, 18.6%, 39% and 53% respectively. The methodology presented here is an efficient and easy to use tool that could help performance analysts in evaluating computer systems.     

Colorimetric Evaluation of Pictorial Coatings in Conservation of Plasterworks from the Islamic Tradition

ABSTRACT

The main aim of our current investigation is the colorimetric evaluation of protective treatments (consolidants) applied to traditional Islamic plasterworks, under natural ageing conditions. From analyses of the original pictorial plaster remains in the Courtyard of the Maidens of the Real Alcázar in Seville, Spain (a World Heritage Site) we prepared test specimens, using materials and techniques similar to the original ones. We analysed 56 test specimens painted with four pigments (yellow, green, blue, and red), using two different binders (animal glue and gum arabic), onto which five representative consolidants were applied: barium hydroxide, acrylic copolymer, polyvinyl butyral, ethyl silicate, and bacterial carbonatogenesis. The test specimens were subjected to natural ageing for one year (indoors and outdoors), enabling a colorimetric assessment to be made of the changes of the polychrome surfaces. The colorimetric heterogeneity of the 56 specimens after ageing registered an average value of 2.7 CIELAB units, assessed using the mean colour difference with respect to the mean. In the aged specimens, the addition of consolidants resulted in average colour differences (mainly lightness differences) of 10.7 and 6.7 CIELAB units, considering as a reference the specimens without consolidants aged indoors and outdoors, respectively. These colour differences were very similar for both binders but not for the four pigments, higher values being found for the blue and red pigments. Considering as reference the samples without consolidants aged outdoors, we found no statistically significant colour differences, either among the five consolidants (p?=?.094) nor the two binders (p?=?.674) used. In addition to the magnitude of colour differences, the choice of the most appropriate consolidants must also consider aspects related to performance and effectiveness. Overall, for the type of paints tested, the polyvinyl butyral consolidant appeared to perform the best, followed by the ethyl silicate.     

A review of ancient Egyptian pigments and cosmetics

The pigments used by the ancient Egyptians constitute the most diverse pigment palette of the ancient world. This review discusses the pigments and binders which were used, arranged principally in terms of the colours themselves, namely, the white, green, grey, black, brown, blue, red, orange, and yellow pigments. The chemical identity of these pigments is discussed with some details regarding the artefacts or time periods from which the pigment concerned has been identified. Combinations of pigments were used for creating some colours, especially: greens, pinks, blues, yellows, and a variety of pale hues by mixing primary colours with a white addition, such as calcite. The identification of ancient Egyptian pigments is often aggravated by chemical interactions between pigment and binder media, or between the pigment and environmental pollutants, or both. The nature of the binders and varnishes used in ancient Egypt is briefly discussed. The identification of green pigments from ancient Egypt is often difficult, and some of the recent research concerning the topic is reviewed. In addition to including relevant details from older literature, this review provides a synopsis of recent studies which have appeared since the last major review carried out by Lee and Quirke in 2000.     

Application of colour metallography in the examination of ancient metals

The use of colour in the metallographic examination of ancient metals is useful both for research and teaching purposes. Application of different optical methods of examination include: polarized light, with or without a first-order red compensator, and differential interference contrast microscopy (DIC). The use of DIC can be combined with the other techniques mentioned in the text for the examination of etched or unetched metal surfaces, which are best observed microscopically using a metallograph. Colour techniques are now used routinely in industrial metallography, and are available for a variety of metals and alloys. Colour tint etching can be used to enhance grain structure or different phases present in the metallic artefact which may not be visible in conventional etched samples, or which lack optical contrast. Many more applications of these techniques in the examination of ancient metals will be published in the literature as they become better known and second-hand equipment with DIC lenses enter the market at a price suitable for conservation laboratories to purchase them.