Blue Wool Research Articles

Manufacturing Variations in ISO Blue Wool Fading Standards under Microfading Exposure Conditions

ABSTRACT As is the case for other accelerated light-ageing methods, microfade test results are usually rated against the responses of the International Standards Organisation’s Blue Wool Fading Standards, the production of which is regulated by the International Standards Organisation. The suitability and convenience of the ISO Blue Wools for this purpose have been questioned on various grounds, including wavelength sensitivity, manufacturing or batch response variations, and the effect of their woven texture on systematic errors. In the present article, the effect of manufacturing variations was assessed by carrying out microfade testing on samples of ISO Blue Wools from various suppliers and manufacturers spanning more than 20 years. Our results confirm that the first three ISO Blue Wools, which are of most relevance to locating colourants at risk of significant light-fading on display in museums, had measurable batch-to-batch and/or manufacturer variations in fading rates, most significantly in the case of Blue Wool 2. Different batches were often also distinguishable by their colour and the texture of the wool fabric. It is argued that while texture-related systematic errors and manufacturing variations are inconvenient, they are not significant in light of the other potential sources of disparity between the results of accelerated exposure tests of any kind and fading at ambient light levels, and it is concluded that the advantages of the use of ISO Blue Wools as internal standards for microfade testing outweigh their disadvantages.

Colouration and Performance Evaluation of Ethiopian Kusha Fibres

ABSTRACT Bast fiber dyeing process is common practice as the value addition of most bast fibers demanded for various commercial and household applications. In this research work, kusha fiber (extracted previously) was subjected to dyeing using direct, reactive, vat and cationic dyes for the first time. Dyeing process was perfrmed using concentrations 0.5%, 1%, & 3% (W/W) dye to fiber with MLR 1:20. After dyeing process, performance of dyed fiber and tensile tests were conducted. The results revealed that K/S value of all dyed kusha fiber samples increases as the concentration of dyes applied increases. The dyed fibers color fastness to washing was found good both in dry and wet rubbing fastness. Reactive dyed samples have shown good rubbing fatness performance over the others. Regarding light fastness, the result shows there was good performance for all samples according to blue wool light fastness standard that exceeds 6. The tensile strength and elongation of dyed samples showed slight decrement both in vat and direct dyed samples; whereas, considerable decrement was observed both in reactive and basic dyed samples due to formation of covalent bond and acid processing medium.

Didactic Panel Illustrating Light Exposure Effects

Abstract 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.

Prediction of the Exposure Endpoint of Textile Color Fastness to Light

The color fastness to light of textile in the product standard is always tested by method 3 in GB/T 8427, which determines the endpoint of exposure according to the discoloration of the blue wool standard sample. The aging of the xenon lamp for exposure resulted in the different sun exposure times of blue wool references required for the same color fastness level. As a result, the difficulty of testing increased, and the test accuracy was also affected. In this paper, the relationship between the exposure time and the service time of xenon lamps was studied through real-time monitoring to accurately predict the endpoint of textile light fastness. The exposure time for color fastness class 3 curve according to the service time of xenon lamp was fitted as: y1=10.4785+6.39539E−5x1+2.53603E−7x1 2; the exposure time of color fastness class 4 underexposure was fitted as: y2=38.17692-0.00131x2+2.78006E−6x2 2-4.81015E−10x2 3; the color fastness to light of textiles wetted with artificial perspiration was y3=13.78014-5.53089E−4x3+1.53274E−6x3 2-2.92228E−10x3 3+1.02685E−14x3 4. The method is practical and effective, has practical value for the light fastness testing of textiles, and has important guiding significance for daily light fastness testing in the future.

Microfade Testing of Fourteen Natural Dyes on Wool: A Comparison of Five Mordants

ABSTRACT Microfade testing (MFT) was used to examine standardized wool samples dyed with 14 natural historic dyes, each prepared with five different mordants, to determine whether the lightfastness and colourimetric properties of these dyes vary as a function of the mordant. The addition of mordants changed the original colour of the dyes as well as potential patterns corresponding to ΔL*, Δa*, and Δb* such that the variation of lightfastness ranges from 0.25–0.70 units of Blue Wool Equivalence (BWE). Disregarding the effect of mordants, MFT showed that all dyes have lightfastness equivalent to BW3, indicating that they belong in the category of ‘high sensitivity to light’. All dye-mordant combinations vary in lightfastness, such that even the least lightfast dye will have a mordant combination that is more lightfast than the most lightfast dye combined with a mordant that renders it less lightfast. The effect of mordants varies by dye: while one dye may demonstrate a difference in lightfastness of 0.56 units of BWE between the least and most lightfast mordant combination, another may show little or no difference (as low as 0.07 units of BWE). Overall, alum based mordants tend to produce the least lightfast combinations, followed by tin and iron, with copper and chromium producing the most lightfast combinations. This paper shows that there are no simplistic patterns of lightfastness between mordant-dye combinations with these 14 natural dyes. Identifying both dye and mordant is useful to better estimate the lightfastness of a dyed textile.

The effect of prior exposure on the lightfastness of early synthetic dyes on textiles

Many studies have investigated light-induced damage to colourants in heritage collections using prepared samples of materials such as artist paints and dyed textiles. The body of research focuses primarily on the response of virgin materials, where colour change is assessed with respect to the original colour as light dose increases. From a practical perspective, most objects in museum collections have accumulated a significant light dose from illumination before acquisition, and subsequent years of exhibit lighting. When considering the risk of further degradation, it is often stated by heritage professionals that fugitive colourants with past light exposure are no longer as sensitive due to the slowing rate of visual damage. This is evident by studying ‘fading curves’, where the rate of colour change typically diminishes with increasing light dose. It remains unclear, however, to what degree the lightfastness of remaining colour changes with ongoing exposure. To address the issue, the light sensitivity of residual colour was investigated as a function of prior dose using a published dataset of colour measurements from textiles dyed with early synthetic colourants in the period of 1874–1905. The CIELAB colour values (D65/2°) for each material and dose increment were used to determine the future dose that causes a just-noticeable difference (JND), ΔE00 = 1.7, starting at different amounts of past exposure. This involved resetting the reference CIELAB values to that of the residual colour after each prior dose. The analysis provides an extension of our earlier work, where only the initial lightfastness was reported. A summary of the findings illustrates the shifting distribution of lightfastness, toward higher Blue Wool (BW) ratings with increasing exposure. As the dose progresses, dyes that start at BW1 sensitivity progress to BW2, then BW3 and so on. The findings from this work may assist with boundary approximations of object sensitivity when prior light exposure is known, or a reasonable estimate is available. An analysis of experimental data is summarised as a tool for this type of decision-making process.

An enhanced optical micro-fading device

This paper introduces a new set-up for the determination of colour change on cultural heritage objects, referred to herein as a stereo-microfading tester. The system uses high quality optics through the implementation of a stereo-microscope as its central element. This technology enables new developments such as incorporation of high quality imaging systems, and separation of fading and colour measurement processes. This paper describes this new micro-fading set-up and evaluates its performance against traditional devices based on the measurement of blue wool standards. The results show a correlation between the fading performance obtained on different devices while highlighting a significant variability inherent to the blue wool samples

Mordant-free dyeing of nylon fabric with mahogany (Swietenia mahagoni) seed pods: A cleaner approach of synthetic fabric coloration

The extraction and consequent application of natural colorants obtained from mahogany ( Swietenia mahagoni) seed pod powder is described here. The colored solution was extracted by facile boiling in an acidic medium. Fourier-transform infrared spectroscopy indicated that the mahogany seed pod extract contained lignocellulosic substances. The typical strong broad band for -OH stretching vibration appeared at around the 3400 cm−1 region in the spectra indicating the presence of alcoholic groups in the substance. The acidic boiling of the mahogany seed pod extract showed the color bearing character at λmax 400–480 nm in the visible range of the ultra-violet spectrum. Subsequently, commercial single jersey-knitted nylon fabric was dyed with the mahogany seed pod extract. The effects of temperature, pH, and time were investigated meticulously for the above dyeing. The optimum conditions for nylon fabric dyeing with the mahogany seed pod extract were selected as the temperature of 100°C, dyeing time of 60 min, and dyebath pH 4.5. The results were interpreted in terms of color strength and fastness properties. The color fastness to wash and perspiration of nylon fabric dyed with mahogany seed pod extract was found to be moderate to good in the grey scale rating 3–4 to 4 grade in the case of optimum dyeing condition whereas color fastness to light was observed to be poor in the blue wool scale rating 2 grade. It was observed that dyeing time, temperature, and pH had profound influences on the color strength of the dyed material. The color strength was increased with the increase of dyeing period and dyebath temperature. The acidic dye liquor produced the darker hues while the alkaline condition had no effect on color yielding. The fabric was dyed uniformly, confirming the evenness of dyeing which is very important for successful commercial dyeing.

Screen printing of cellulose electrospun nanofibres with PDA polymer

Herein, the preparation of print paste formulation containing the PDA (Polydiacetylene) polymer has been investigated for the first time. Screen printing method was employed to apply the prepared print paste on cellulose ENMs, and the Electrospinning method was used to fabricate cellulose acetate ENM followed by its deacetylation to prepare CEL ENMs. Distinct blue colour was developed with 254 nm UV-irradiation of printed CEL ENMs. We achieved good colour strength (K/S = 3.1) on printed ENMs, excellent colourfastness to washing (staining on multifibre: rating 5) and colourfastness to light (blue wool scale: rating 1). We found that the printed CEL ENMs can be effectively used as thermochromic sensor as it induced blue-to-red colour transition at 80 °C. Moreover, it has demonstrated solvatochromic property when incubated in NaOH. Mechanical properties (Tensile strength and wrinkle recovery), chemical structure (ATR-FTIR spectroscopy) as well as surface morphology (SEM analysis) of ENMs were also determined.

Quantitative Assessment of Impact and Sensitivity of Imaging Spectroscopy for Monitoring of Ageing of Archival Documents

Ageing of historical documents often results in changes in the optical properties of the constituent materials. Imaging spectroscopy (IS) can be a valuable tool for monitoring of such changes, if the method fulfils two important conditions. Firstly, compared to natural ageing, the accumulated light dose from repeated measurements of the monitored document must not induce any significant degradation. Secondly, the monitoring instrumentation and procedures should be sensitive enough to detect changes in the materials before they become visible. We present experimental methods to evaluate the suitability of IS instrumentation for monitoring purposes. In the first set of experiments, the impact of repeated monitoring measurements was determined using a set of Blue Wool Standard materials. In the second set of experiments, the capability of the instrument to detect spectral changes was tested using ISO standard materials and several documents representative of European archive collections. It is concluded that the tested hyperspectral instrument is suitable for monitoring of the colour change of documents during display. The described experimental approach can be recommended to test the suitability of other imaging spectroscopy instruments for monitoring applications.

The Impact of Total Radiation Flux on Organic Materials under LED Lighting

In this study, an accelerated aging experiment for fabric and paper was conducted using two light emitting diode(LED) sources with different wavelength characteristics, and the discoloration under each lighting type was examined. Hanji(Korean traditional paper) and related textiles showed more discoloration under blue LEDs, while the blue wool standard showed more discoloration under white LEDs. This, indicated that the deterioration varied depending on the sample color. The the effect of the light source on artifact deterioration was primarily related to the total radiation flux(expressed in mill watts), rather than the total luminous flux(expressed in lumens). In addition, the discoloration of the investigated artifacts was dependent on the color rendering of the lighting.

Colored feathers in museum collections: A spectroscopic study of 3 bio-pigments and their lightfastness

Abstract Yellow to red feathers in ornithological and ethnographical museum collections are known to be sensitive to light exposure. However, only a few studies on the interaction of light with the color of feathers have been published. This work provides fresh insight into the sensitivity of feathers for better conservation and exhibit of ethnographic collections, with a specific focus on carotenoids, psittacofulvins and porphyrins-based feathers. A first approach was to evaluate the use of Fiber Optics Reflectance Spectroscopy (FORS) in the visible range to characterize the chemical nature of the bio-pigments. It was implemented on 19 ornithological specimens preserved in the Museum national d’histoire naturelle (MNHN) in Paris, and on assigned feathers from more than 40 objects from the collections of the musee du quai Branly - Jacques Chirac (mqB-JC). Then, microfading tests were carried out on molting feathers or picked up on dead birds. Two different setups were used in order to determine a reproducible protocol for these 3D materials. Several variables were considered including the positioning of the feather and the duration of measurements. In addition to the visible range, the near-infrared (NIR) region was also investigated to determine if the color fading is concomitant to any structural modification. Then the developed protocol was applied on some loose lumps of feathers from objects of the mqB-JC collections. The data were compared against each other and to the Blue Wool Standards fading rates.

K‐M theory of fabric knitted by three‐channel rotor spun wool yarn

AbstractTwo‐component and three‐component color blended yarns were spun by red, yellow, and blue wool slivers using a three‐channel rotor spun machine, and the corresponding plain fabrics were knitted. The color‐matching models of K‐M theory were built with the relative method and the least squares method, respectively. Colors and blending ratios of the fabrics were predicted by the model. The results showed that the average color differences of the samples predicted by the two methods are both about 1.0 and the mean value of the proportional error is below 3%. The least squares method has a better color‐matching effect for the three‐component sample, and the relative value method has better color‐matching results for the two‐component sample. When the tolerance range is 2.0, the pass rates of the samples predicted by either the relative value method or the least squares method reach 100%.

Identification of dyes in Egyptian textiles of the first millennium ad from the collection Fill-Trevisiol

High-performance liquid chromatography coupled to a diode-array detector (HPLC-DAD) is used to investigate 30 samples which were removed from 27 ancient Egyptian fabrics of the Fill-Trevisiol collection. Attention is focused in this paper on fabrics of the Roman and Byzantine periods, with red and deep violet–blue wool weft threads which are Z-spun. The following dyes are identified in fabrics which date to the Roman period (first–fifth c. ad): mollusc purple, madder, and indigo/woad (Indigofera species and other, Isatis tinctoria L.). The results for the Byzantine (fifth–seventh c. ad) fabrics are richer in terms of identified dyes: apart from the three aforementioned dyes, the use of kermes (Kermes vermilio Planchon) and cochineal is revealed as the two coccid dyes have been detected in six Egyptian–Byzantine fabrics. Moreover, a yellow dye (probably Reseda luteola L.) is identified in one sample. Finally, samples taken from two fabrics, which date to the Islamic period, were dyed using indigo/woad and lac (Kerria lacca, Kerr). Mixing madder and indigo/woad to imitate true purple was a common practice in ancient Egypt and this is confirmed by the HPLC results in several samples. Semi-quantitative results are obtained from the HPLC peak areas and lead to the following conclusions. Madder dyes which were rich or poor in alizarin, compared to purpurin, and could have been therefore obtained from Rubia tinctorum L. and Rubia peregrina L., respectively are detected in Byzantine fabrics. Only alizarin-rich madder dyes are identified in some samples from Roman fabrics, but in some other samples the relative alizarin-to-purpurin ratio cannot be measured with confidence. Cochineal is found in two samples. The biological source of cochineal (Porphyrophora hamelii Brandt) is possible to be chemically identified only in one sample. The HPLC results of the molluscan dye detected in a Roman fabric are compared with the relative compositions of extracts of the three Mediterranean molluscs leading to the speculation that the Roman purple sample was probably dyed using Hexaplex trunculus L. The molluscan dye was furthermore detected in a Byzantine sample where it was combined with madder. Finally, it is reported that the standard (hydrochloric) acid hydrolysis method which is commonly applied to extract dyes from archaeological samples does not have any noticeable effect on the relative composition of the molluscan dye.

An Assessment of the Deterioration of Fabricated Metal Thread with Light, and Temperature and Humidity Factors: A Focused Study of Asian Textile Collections at the Metropolitan Museum of Art, New York

To investigate the deterioration of textiles with metal thread, I surveyed 40 textile objects, dating from the 11th to the 19th century from Korea, China, Japan, and Central Asia at the Metropolitan Museum of Art, New York. This survey included various types, widths, and thicknesses of metal thread. In addition, deterioration was examined under the microscope and color information was collected using the spectrophotometer. While investigating metal thread in the collections, I fabricated 12 different types of metal samples with metal leaf(24K gold, silver, and copper leaf), adhesive (hide animal glue and a mixture of hide animal glue and iron oxide red), and paper substrate(Korean mulberry and Taiwanese kozo paper). The accelerated deterioration process of those fabricated samples was carried out using a light box(UV and daylight), and a humidity cabinet. In the light experiment with blue scales textile fading card(aka, blue wool standard), the metal leaf began to peel off during the deterioration process with 756,000 lux-hours UV and daylight. In the temperature and humidity experiment, I could observe the reddish tarnish on copper, and some part of it began to peel off. Color reading on the light exposed samples showed that the degree of color change on the surface follows the amount of exposure as it increased over time. On the other hand, color change on the samples after artificial deterioration using temperature and humidity factors showed random change of color with occasional spikes. Distortion of original shape worsened in the samples exposed to temperature and humidity.

Measuring photostability through glass: the application of microfading testing to the study of framed pastel artworks

Paper‐based heritage objects on exhibition are typically framed using a transparent glazing material such as glass or acrylic. This often makes the task of measuring their light fastness a difficult one since cultural institutions may have unframing restrictions, especially for large‐format objects. However, a testing programme recently conducted at the National Museum in Krakow has revealed that in certain cases it is possible to obtain colorant stability information directly from a framed object. Microfading testing results are reliable if the distance from the object to the protective glazing is adequate to allow proper illumination and collection of reflected light. This paper presents a case study of six large‐format pastels on paper by Stanisław Wyspiański, one of the most outstanding and versatile artists at the turn of the twentieth century in Poland. Some of the orange and pink areas showed higher sensitivity to light with fading rates that remain within the Blue Wool 1–2 range. The objects have been classified according to the light sensibility of their colorants, and this information has allowed development and implementation of exhibition guidelines that serve to minimise the degradation associated with museum illumination. In addition, scientific imaging, microfading data and computer analysis of the images have allowed virtual representation of the potential colour changes that these artworks may experience as a result of uncontrolled and long exposure to gallery illumination.

Comparing Colorfastness to Light of Wood-Staining Fungal Pigments and Commercial Dyes: An Alternative Light Test Method for Color Fastness

Colorfastness to light is an essential quality for textiles exposed to sunlight for a significant length of time. In this study, the colorfastness (specifically to light) of fabrics dyed with wood-staining (spalting) fungal pigments was compared to the colorfastness of commercial dyes. A short-duration immersion dying method without heat was used to minimize both water and energy usage. Both mordanted and unmordanted fabrics were tested and compared for colorfastness. Additionally, a new method of testing for colorfastness to light was developed. Results indicate that the wood-staining fungal pigments demonstrate superior colorfastness to light over commercial dyes when the employed dyeing method is used. Additionally, the colorfastness to light testing method developed using the L-2 Blue Wool Standard and QUV Accelerated Weathering Machine is a viable alternative to current standard colorfastness to light testing methods.

A study of the light sensitivity of birch bark

ABSTRACTBirch 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.

A microfading survey of the lightfastness of blue, black and red ballpoint pen inks in ambient and modified environments

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.

A classification system to enhance light‐fastness data interpretation based on microfading tests and rate of colour change

In general light‐fastness tests are carried out by comparing the colour change of a sample to the colour change of Blue Wool Standards in the same illumination conditions. With the microfading technique, developed to test the light fastness of a tiny test area on objects of cultural value, this comparison is made by absolute colour change after exposure. This article presents a new approach to enhance data interpretation of light‐fastness tests by the use of the rate of colour change. The procedure is combined with the conventional classification process using absolute colour change. The new classification system with the rate of colour change was applied to 44 samples, 13 of them were classified in more sensitive Blue Wool categories when analysing the rate of colour change. The perspective of rate of colour change helps to enhance data interpretation especially of samples showing fading characteristics different from the light‐fastness standards.