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.     

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.     

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.     

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.     

A study of the light sensitivity of birch bark

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.     

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.     

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.     

Autocentering equipment for the radiography of paintings

Abstract

New equipment is described which allows precise location of the X-ray source under the portion of interest of a painting undergoing radiography. It utilizes an electromagnetic wave transmitter placed on the painting and four sensors on the movable carriage containing the X-ray tube which process the signals and indicate, by an LED display, the necessary movements of the carriage.     

基于科研产出关联的大科学装置集群规划布局分析方法研究——以粤港澳大湾区综合性国家科学中心为例

[目的 /意义]提出一套分析框架,可用于为大科学装置集群规划时装置的关联性论证提供参考等,有助于为大科学装置规划布局提供前瞻性的定量化参考,作为以需求驱动规划的补充。[方法 /过程]从科研成果入手,应用科学计量学方法,提出基于科研产出关联的大科学装置集群规划布局分析框架,包含确认分析对象、获取装置数据、装置知识分布描述、装置关联分析等流程与方法。以粤港澳大湾区综合性国家科学中心为例,收集已布局大科学装置（散裂中子源与同步辐射光源）与规划布局的大装置X在国际上同类型装置的论文数据,从多个层次分析其学科层面的内在关联。[结果 /结论 ]依托大科学装置发表论文数量持续上升;三类大科学装置均具有较强的学科交叉性,不同装置的交叉学科存在差异;三类装置关联性不一,已有装置（散裂中子源与同步辐射光源）关联度高,存在可能的互补关系,大装置X与已有装置关联度则较低,如要布局建议还需要进一步专家论证。提出的方法具有可行性,在一定程度上能为大科学装置规划布局提供前瞻性的定量化参考。     

平板扫描仪的散射光效应

本文从光源作用于测试图极端阶调区域后对中性灰还原影响的角度测量了平板扫描仪的散射光效应，为此设计了置于黑色和白色背景的等距离分布灰色块测试图。实验结果表明，三种被测试的不同类型的平板扫描仪确实存在散射光效应。     

'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.     

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.     

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.     

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.     

现代图书馆公共空间设计发展的新趋势

图书馆公共空间是社会化的行为场所,其设计应该最大限度地满足人们的不同需求并充分体现人性化。图书馆公共空间设计的要素主要包括光环境、材质与色彩。随着社会的不断进步,现代图书馆室内公共空间设计呈现出一些新趋势:由平面空间转向立体空间;光环境与色彩设计更加人性化;绿色、生态、低碳设计日益兴起;趋向智能化,舒适度增加,保持民族化,注重科学性,加入减噪设计等。     

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.     

Cinnabar reviewed: characterization of the red pigment and its reactions

Abstract

In the majority of cases, the red color of cinnabar on objects of cultural heritage is well preserved, though turning black is often claimed and has been the subject of investigations. To evaluate conditions for the stability of the pigment and understand the reactions, in this paper the problem is approached from various viewpoints. First of all the natural form cinnabarite is compared with the artificially prepared pigment vermilion. This establishes a differentiation of types in terms of quality, depending on structural impurities. With regard to the pigment's reactions influencing the discoloration, the most commonly mentioned environmental factors, such as radiation or halogens, are evaluated. In relation to various usages, the pigment's structural stability is then viewed in connection with adjacent pigments, glues, and the substrate, which may lead to a brown or black coloration or even the release of mercury, whereas the color is preserved in most cases when used on lime or in ink and lacquer. Due to the materials’ properties, attention is drawn to the fact that discoloration to a brownish-black is not necessarily a sign of damage and harmful reaction products, but may indicate good preservation of the painted material, provided that the mercury can be bound in the substrate.     

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.     

Searching strategies for the Bulgarian language

This paper reports on the underlying IR problems encountered when indexing and searching with the Bulgarian language. For this language we propose a general light stemmer and demonstrate that it can be quite effective, producing significantly better MAP (around + 34%) than an approach not applying stemming. We implement the GL2 model derived from the Divergence from Randomness paradigm and find its retrieval effectiveness better than other probabilistic, vector-space and language models. The resulting MAP is found to be about 50% better than the classical tf idf approach. Moreover, increasing the query size enhances the MAP by around 10% (from T to TD). In order to compare the retrieval effectiveness of our suggested stopword list and the light stemmer developed for the Bulgarian language, we conduct a set of experiments on another stopword list and also a more complex and aggressive stemmer. Results tend to indicate that there is no statistically significant difference between these variants and our suggested approach. This paper evaluates other indexing strategies such as 4-gram indexing and indexing based on the automatic decompounding of compound words. Finally, we analyze certain queries to discover why we obtained poor results, when indexing Bulgarian documents using the suggested word-based approach.