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.     

Lighting the Shroud of Turin for Exhibition in 2015

ABSTRACT

Lighting a cultural heritage artifact requires balancing visual perception with preventive conservation, by providing the best lighting (in terms of spectral distribution and quantity) to enable the viewer to appreciate details and color, while limiting photo-induced degradation. The paper outlines the methodology applied by a multi-disciplinary team while lighting the Shroud of Turin at its last public exhibition in 2015. The methodology considered the special requirements of the Shroud, including exposure to ultraviolet light, while providing appropriate display conditions that would meet audience expectations. The desired appearance (readability of the body image and color) was defined with the help of Shroud researchers and confirmed by subjective tests, while appropriate light levels for preservation were set in agreement with standard requirements and using knowledge of the degradation of linen in visible and UV light. The installation provided a controlled environment and a managed visitor route to the Shroud, assuring excellent perception of both details and color, with the lowest illuminance level about 15?lx.     

Reflections on light monitoring: Evaluating museum lighting options for modern and contemporary art

Spectrometric handheld light meters that can provide adequate data for evaluation of replacement bulbs for contemporary art objects are now commercially available. This approach was taken to assess potential replacements for the incandescent street lamps in Chris Burden's Urban Light at LACMA, Los Angeles, USA. These meters are also useful tools for monitoring and characterizing museum lighting, which are currently done with illuminance (lux) meters. The new spectral light meters will enable conservators to tailor lighting recommendations for individual artworks, when spectral information from these meters is combined with damage function data on artists’ materials. The latter information can be obtained for some materials by a small modification to the microfade testing procedure, as exemplified by microfading colored samples Henri Matisse created during the design phase for La Gerbe.     

Conservation of a room: A treatment proposal for Mark Rothko's Harvard Murals

A treatment with projected light for Mark Rothko's Harvard Murals (1962) is proposed. The group of five paintings on canvas has changed color due to the presence of a fugitive red pigment and excessive exposure to natural light in a room with large windows. For the conservation of Rothko's Harvard room, it is brought into context within his other commissions and environments. The original color of the works is determined by the digital restoration of contemporary photographs. With a camera projector system a compensation image is calculated that is projected onto the original canvas resulting in a restored color appearance. This approach of inpainting with light is compared with considerations of cleaning and inpainting in conventional conservation treatments. Overall lighting and architecture including the unusual wall color carefully chosen by Rothko play a key role in the treatment of the Mural cycle as an environment.     

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.     

Mitigation of light-induced damage on modern digital prints: Photographs and documents

This study is part of a larger research project dedicated to digital print preservation issues – the Digital Print Preservation Portal (DP3). This work quantifies the potential of glazing materials to mitigate different types of light-induced damage – colorant fade, paper yellowing, changes in paper gloss, and loss of optical brightening agent (OBA) function – that occur to digitally printed photographs and documents when on display. Prints were subjected to xenon lighting to simulate daylight through window glass in a series of arrangements: without glazing, with plain framing glass (soda-lime) in a sealed or unsealed package, and with UV blocking glass in a sealed or unsealed package. Sealed packages served the purpose of isolating the samples from atmospheric pollutants, known to contribute to the deterioration of certain print types. In this study, the use of UV-filtering glass protected prints from colorant fade, paper yellowing, and paper gloss change to an extent. Protection conveyed by plain glass was less comprehensive and less effective than UV glass. Neither type of glazing was able to keep the OBAs functional by the end of the light exposure. It was also seen that light-induced damage to digital prints is due not only to UV radiation, but also to visible light, and that different digital prints may be more vulnerable to one or the other. Protecting sensitive prints from UV radiation and budgeting the amount of light they may be exposed to should be essential to any print display policy in order to ensure longevity.     

Light-induced cracking and abrasion of inkjet prints: Damage and mitigation

This study is part of a larger research project at the Image Permanence Institute dedicated to digital print preservation issues – the Digital Print Preservation Portal (DP3). Previous DP3 studies determined that certain digital print types are prone to cracking and/or abrasion, and that factors such as low relative humidity, pollutants, and light increase the brittleness of the ink-receiving layer of some inkjet papers. The purpose of this investigation was to explore if light also increases the propensity of inkjet prints to abrade, and to examine the potential of framing glazings to mitigate light-induced physical damage (cracking and abrasion) by attenuating some portion of the UV spectrum. Inkjet papers and prints were subjected to xenon lighting (to simulate daylight through window glass) without glazing, or in sealed framing packages with plain framing glass (soda-lime) or UV filtering glass. Before and after light exposure, brittleness, and abrasion resistance were evaluated independently using two tests: ISO 18907 (Imaging materials – Photographic films and papers – Wedge test for brittleness) and a rub test utilizing a Sutherland® Rub Tester. In this study, exposure to light increased the cracking and/or abrasion tendency of some specimens. The use of UV filtering glass reduced this light-induced propensity in all cases. Plain glass protected all samples from at least one of these two types of surface damage, but was less effective than UV glass. Light-induced brittleness and sensitivity to abrasion were mostly, though not exclusively, caused by UV radiation. It was also seen that some prints may become brittle and/or prone to abrasion in the absence of image fade. Budgeting the amount of light these objects can be exposed to, protecting them from UV radiation, and handling prints with caution especially after exhibition, is essential in order to limit physical damage.     

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.     

‘Tales of Japan’: a travelling exhibition of Japanese art from the New York Public Library

Abstract

Acrylic polymer dispersions, regularly used as artists' media or varnishes, were monitored for the development of yellow discoloration under natural aging conditions for a period of two years. Films of a number of water-based acrylic artists' media were kept under visible light of either moderate (150 lux) or low (50 lux) intensity (cycled on 10 hours per day) and were compared to films kept in dark storage, which have been observed to yellow. Results after two years show that exposure to visible light at 150 lux effectively prevented film discoloration in a number of products, and seemed at least to slow the rate of yellowing in others. Exposure to low-intensity (50 lux) lighting was found to be less effective in preventing this yellowing.     

'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.     

Modeling of Light-Induced Changes in Reflectance Spectra: A Predictive Tool for the Effect of an Arbitrary Spectral Irradiance

Optical radiation is capable of altering the spectral reflectance of layers of colorants. Light damage is of particular importance in respect to unique historical objects in exhibitions. The major parameter governing this process is the spectral irradiance applied to the surface. As this may vary significantly for different light sources, an experimental investigation of the damage potential of the numerous illuminants available is a cumbersome task. In this work a numerical algorithm for the prediction of modifications of the spectral reflectance of colorants subject to a given arbitrary spectral irradiance over a given time is presented. It uses the temporal evolution of the spectral reflectance of the dye or pigment at issue when irradiated by a set of narrowband light sources as input data. The predicted reflectance spectra and the resulting color changes are compared to those measured for samples irradiated with common polychromatic light sources. The concept described in this work aims at the implementation of a standardized procedure and database for the prediction of radiative damage for a comprehensive range of pigments and dyes.     

An Open Source ILS Glossary: Version 2

This article is a glossary of terms one finds in open source integrated library systems (ILSs). The focus of this glossary is on the two major open source ILSs—Evergreen and Koha. These are being used in an increasing number of U.S. and Canadian public libraries as well as other types of libraries. The glossary is an introduction to the terms that those working with these open source library systems use on a day-to-day basis, with links to sources with more information for those new to open source projects.     

广告摄影用光分析

广告摄影画面别具一格、匠心独运的表现与刻画,很大程度上取决于用光。明晰人工照明光源的基本要素,及其各要素之间相互联系,相互影响的关系,做到合理、正确的调度与控制照明光源,以达最终控制与明确把握形象、质感、色彩、画面气氛与空间关系。     

Cross-Cutting Effects of Hypertext Navigation on the Convergence of Attitudes

This study explores the navigation patterns of users reading hypertext-linked online news articles about a controversial issue. With the theoretical frameworks of selective exposure and cross-cutting exposure, the study examined the effects of individuals’ attitudes on their navigation patterns and consequent attitude changes after the news exposure. We asked 130 participants to read positive or negative news articles about the Korea–U.S. free trade agreement (FTA) by selecting six consecutive webpages. The results indicate that their attitudes toward the FTA was a significant predictor of their news selection, providing support for the selective exposure hypothesis. In terms of navigation patterns across the six news selection stages, the participants tended to select news articles that corresponded to their initial attitudes. The selection gap between participants with different attitudes increased until the fifth stage and ultimately converged. In terms of attitude change, the gap in the participants’ attitudes decreased sharply after their navigation.     

Measuring Weathering and Nanoparticle Coating Impact on Surface Roughness of Natural Stones

ABSTRACT

The surface texture of a stone represents a sensitive parameter in evaluating its conservation state. In monuments and sculptures, in fact, external agents continuously alter the appearance of stones, determining peculiar weathering patterns and modifying properties such as retention of water and particles, interaction with light, color, and finishing. The application of protective coatings also determines changes in surface appearance of a stone, usually evaluated and monitored by color change tests. Surface metrology methods offer the possibility to quantify these changes, evaluating the impact of external agents (natural, i.e. weathering, and artificially, i.e. protective coatings) on natural stones. In this research, we demonstrate the potential of surface areal measurements in describing the evolution of weathering processes and the effects of protective treatments on porous stone materials. The obtained results suggest that the extent of the modifications is related to the scale of observation (small- vs. large-scale undulations, i.e. roughness and waviness, respectively), with an overall increase of surface roughness as the weathering proceeds. Unexpectedly, coatings based on nanoparticle dispersions increase the topographic height parameters, due to the absence of a homogeneous film.     

Reference as an Access Service: Collaboration Between Reference and Interlibrary Loan Departments

ABSTRACT

Academic libraries increasingly rely on Interlibrary Loan (ILL) departments to obtain research materials. This adds to the workload of ILL at a time when many libraries are experiencing budget cuts and dwindling staff. Collaboration between ILL and Reference can assist ILL by providing searching expertise. Collaboration is facilitated by the paperless environment provided by ILL management software. Patrons benefit from increased fill-rates and reduced turnaround time for ILL requests. Reference benefits by exercising creative searching for difficult-to-find materials and gaining exposure to new reference sources and online catalogs. These benefits are explored through analysis of fill-rates, sources from which materials were ultimately obtained, sources used by the Reference Department, and interviews with staff.     

Confirmation biases in selective exposure to political online information: Source bias vs. content bias

The present work examines the role of source vs. content cues for the confirmation bias, in which recipients spend more time with content aligning with preexisting attitudes. In addition to testing how both source and content cues facilitate this biased pattern of selective exposure, the study measures subsequent attitude polarization. An experiment (N?=?120) presented messages with opposing political stances, associated with unbiased or slanted sources. Software tracked selective exposure in seconds, and attitudes were measured before, immediately after, and two days after message exposure. Further, information processing styles were assessed. The confirmation bias emerged regardless of source quality. Information processing styles moderated the confirmation bias as well as selective exposure to messages from unbiased vs. slanted sources. Selective exposure reinforced attitudes days later.     

Exposure of artists' colorants to airborne formaldehyde

Abstract

Thirty artists' colors have been exposed for 12weeks to 120ppb of formaldehyde in purified air as well as to purified air alone (control experiment). The exposure was carried out in the dark at ambient temperature (19 ± 2°C) and humidity (RH 44–52%). Color change (?E) was measured using a reflectance color analyzer after one, two, three, four, six, eight, 11 and 12 weeks of exposure. Color parameters (x, y, X, Y, Z, L*, a*, b* and ?E)"were also calculated from the 380–700nm spectra, recorded with a reflectance spectrophotometer, of unexposed colorants and of colorants exposed for 12 weeks to purified air and to formaldehyde. Regression analysis of the two data sets indicated that the color changes measured by these two methods were in excellent agreement (nearunity slopes, with correlation coefficients > 0.99). Exposure to either formaldehyde or pure air on watercolor paper resulted in little or no color change for all the colorants tested, including inorganic colorants, alizarin lakes, quinacridones, triphenyl methanes, indigo derivatives, arylamides and natural colorants such as curcumin. Formaldehyde, which is ubiquitous in indoor air, including museum air, does not appear to be a major threat to colorants in museum collections.     

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°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.     

Information systems and collection development in public libraries

Collection development in public libraries is performed by one or more librarians who make use of a variety of selection tools. Computers and information systems are becoming increasingly important tools for selectors because they offer alternatives for assessing user needs, for gathering information about published materials, and for obtaining materials quickly. This paper describes a case study of twelve public library systems, the tasks they perform, and the sources they use in collection development. The selectors reported satisfaction with their jobs, increasing reliance upon information systems and electronic resources, and the need for system improvements to support selection for local collections in a publishing climate responsive to popular taste.