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A picture of the upgraded microfading spectrometer showing the light source (blue box), spectrometer (black box above the light source), the probe on the right attached to a motorised linear stage, the input and output fibre optics attached to the probe and a sample placed on a motorised stage
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This cross-sectional survey assessed the knowledge and perceptions of migraine among Saudi Arabian individuals. The study was conducted over three months in 2023 (1st of June 2023 to 31st of August 2023) using a prevalidated onl...
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... Over the last two decades, the field of micro-fadeometry has developed rapidly; many institutions acquired micro-fading instrumentation 3 and new set-ups have emerged [12][13][14] . The technique has successfully proved its ability to identify light sensitive materials and classify them according to a reference scale currently based on blue wool standards (DIN EN ISO 105-B02 [15] ) [16] . ...
... First of all, the results show fading behaviours that are in agreement with the indication of the manufacturer reporting a factor of approximately two between each subsequent blue wool category 12 . Secondly, no significant differences in the E * 00 values values between the two modes of operation (co-axial vs traditional; both modes used the HPX lamp) have been observed 13 , which is consistent with the fact that the fading process is similar from one mode to another -in other words the amount of energy received by the samples is identical in both modes. At first glance, the spectral power distribution of the light source does not seem to affect the colour change behaviours, which are comparable from one lamp to another when a radiometric scale is used ( Fig. 10 , (a)) 14 . ...
... A more rigorous compar-12 https://www.james-heal.co.uk/essentials-blue-wool-standards-how-to-use/ (consulted on 17/06/2021). 13 A graph is available in S.I. n °05. 14 A graph of Figure 10 using a photometric scale (klux-hr) is provided in S.I. n °06. ...
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
... powder pigment) or mock-ups prepared in the laboratory consisting of combinations of two or more materials (e.g. pigment/binder system) [12,13]. Recently there has been considerable interest in the use of MFT and the number of cultural institutions currently using or considering construction or purchase of a MFT device increases steadily [14]. ...
... In addition to experience, a careful selection of the testing areas is recommended along with monitoring and documentation of the tested spot using imaging methods. Liang et al. have measured the profile of the incident spot of a retroreflective microfading spectrometer using a CCD camera finding that the minor axis of the spot was approximately 0.46 mm full-width at half maximum (FWHM) [12]. Whitmore employed a similar approach to the thermal or photopaper method mentioned above to determine a 0.4 mm diameter for a test area using his original instrument [1]. ...
... After analyzing and measuring the spot, it was observed that even at the proper working distance a relatively higher size of the spot was obtained relative to the other methods employed. The diameter of the MFT beam acting on the analyzed surface has been reported to be up to 0.5 mm [1,3,12,42]. The 1.2 mm value obtained using digital photography seemed too large indicating that a different measurement method was necessary. ...
Microfading testing allows to evaluate the sensitivity to light of a specific artwork. Characterization of the illumination spot is important to determine its shape, dimensions, light distribution, and intensity in order to limit and account for possible damage. In this research the advantages and disadvantages of several methods used to determine the beam shape and intensity profiles are described with the aim of providing various options to microfading researchers interested in characterizing their irradiation spots. Conventional and imaging methods were employed and are compared in terms of their accuracy, cost, reliability, and technical features. Conventional methods consisted of an aperture technique using aluminium foil and four different materials namely stainless steel, silicon, muscovite, and Teflon used as sharp edges. The imaging methods consisted of digital photography of illumination spot, direct beam measurement using a CMOS camera, and direct beam measurement using a laser beam profiler. The results show that both conventional and imaging methods provide beam width measurements, which are in satisfactory agreement within experimental error. The two best methods were direct measurement of the beam using a CMOS camera and sharp-edge procedure. MFT illumination beam with a CMOS camera followed by a determination of the beam diameter using a direct method, more specifically one involving a sharp-edge technique.
... powder pigment) or mock-ups prepared in the laboratory consisting of combinations of two or more materials (e.g. pigment/binder system) [12,13]. Recently there has been considerable interest in the use of MFT and the number of cultural institutions currently using or considering construction or purchase of a MFT device increases steadily [14]. ...
... Ford has noted that these changes preclude thermal damage to objects or have an in uence on fading rates and mechanisms [3]. Liang et al. have measured the pro le of the incident spot of a retrore ective microfading spectrometer using a CCD camera nding that the minor axis of the spot was approximately 0.46 mm full-width at half maximum (FWHM) [12]. Whitmore employed a similar approach to the thermal or photopaper method mentioned above to determine a 0.4 mm diameter for a test area using his original instrument [1]. ...
... Image analysis shows that the MFT illumination beam has a top-hat shape, which indicates that the irradiated area receives a uniform amount of energy throughout the entire area analyzed. A MFT beam previously characterized by Liang et al. also exhibited a top-hat pro le along the minor axis and near tophat shape along the major axis [12]. An evaluation of the MFT optical setup revealed a dependence of the measured signal on the working distance. ...
Microfading testers have become widely accepted by the conservation science community for establishing and recommending appropriate lighting conditions that minimize damage to collections. These devices offer the opportunity of measuring the photostability of cultural heritage objects due to their optical setup, which allows to conduct and quantify accelerated photoaging over a spot of approximately 0.5 mm. Also, by using a high sensitivity photodetector it is possible to measure spectrocolorimetric change before it is perceived by the human eye. Although a considerable amount of testing is currently performed with these instruments, there are still safety concerns in terms of possible damage to the objects due to the use of a high intensity spot during testing. Nevertheless microfadeometry is widely considered a nondestructive technique. The advantages and disadvantages of several methods used to determine the beam shape and intensity profiles are described with the aim of providing various options to microfading researchers interested in characterizing their irradiation spots. Conventional and imaging methods were employed and are compared in terms of their accuracy, cost, reliability, and technical features. It has been found that both methods provide beam width measurements in satisfactory agreement within experimental error.
... Examination of spectra might also suggest testing errors; as previously mentioned, parallel shifts across the entirety of the spectrum could indicate movement of the sample or test head during the MFT run, requiring retesting of that color. Liang et al. (2011) advocated for the advanced exploration of MFT spectra, as this can provide more insight into degradation processes than reliance on colorimetry alone; a proposed approach is to calculate the difference in reflectance (final minus initial) across the visible region and determine the rate of change of the spectrum for narrow wavelength ranges (25 nm or 50 nm windows). ...
... Compared with a typical ns-pulsed laser with repetition rate of 10-100 Hz and pulse duration of ∼5 ns, a CW laser can have a measurement advantage of up to 7 to 8 orders of magnitude in efficiency, if the damage threshold is comparable to the intensity of a typical CW laser in remote operation. For example, highly light sensitive pigments such as cochineal, orpiment and realgar will be in this category [12]. For a pigment of medium sensitivity to laser induced degradation such as red lead, the damage threshold of ∼10 6 W cm −2 [13,14] means that the detection efficiency is about an order of magnitude lower for an ns-pulsed laser compared with a 50 mW CW laser assuming a spot size of a few mm in diameter. ...
Portable and mobile Raman spectroscopy systems are increasingly being adopted in in situ non-invasive examination of artworks given their high specificity in material identification. However, these systems typically operate within centimeter range working distances, making the examination of large architectural interiors such as wall paintings in churches challenging. We demonstrate the first standoff Raman spectroscopy system for in situ investigation of historic architectural interior at distances > 3 m. The 780 nm continuous wave laser-induced standoff Raman system was successfully deployed for the in situ examination of wall paintings, at distances of 3–15 m, under ambient light. It is able to identify most common pigments while maintaining a very low laser intensity to avoid light induced degradation. It is shown to complement our current method of standoff remote surveys of wall paintings using spectral imaging.
... However, degradation is sometimes more subtle than what is visually perceptible under a microscope. Table 2 compares the intensity and fluence of typical laser sources used in OCT, NLM, micro-Raman as well as the Xenon light source used in the well-known (in preventative conservation) in situ accelerated light ageing technique microfade [33][34][35]. Detailed studies of laser induced damage for micro-Raman spectroscopy has been conducted (e.g. Burgio et al. [36]) and the tabulated values for micro-Raman are the maximum intensity normally used to avoid laser induced damage. ...
... Some of the most light sensitive pigments such as realgar and Prussian blue were examined [34,35]. The samples were repeatedly scanned with the 810nm OCT (the spectral range of the supercontinuum source incident on the sample is 600-1000 nm) for 400 times in an area equal to the spot size of our fibre-optic spectrometer probe (3 mm diameter). ...
This paper examines for the first time the potential complementary imaging capabilities of Optical coherence tomography (OCT) and non-linear microscopy (NLM) for multi-modal 3D examination of paintings following the successful application of OCT to the in situ, non-invasive examination of varnish and paint stratigraphy of historic paintings and the promising initial studies of NLM of varnish samples. OCT provides image contrast through the optical scattering and absorption properties of materials, while NLM provides molecular information through multi-photon fluorescence and higher harmonics generation (second and third harmonic generation). OCT is well-established in the in situ non-invasive imaging of the stratigraphy of varnish and paint layers. While NLM examination of transparent samples such as fresh varnish and some transparent paints showed promising results, the ultimate use of NLM on paintings is limited owing to the laser degradation effects caused by the high peak intensity of the laser source necessary for the generation of non-linear phenomena. The high intensity normally employed in NLM is found to be damaging to all non-transparent painting materials from slightly scattering degraded varnish to slightly absorbing paint at the wavelength of the laser excitation source. The results of this paper are potentially applicable to a wide range of materials given the diversity of the materials encountered in paintings (e.g. minerals, plants, insects, oil, egg, synthetic and natural varnish).
... During the same period, Pretzel (2000) was also independently developing a similar micro-spot fading test at the Victoria and Albert Museum. During the last 15 years, research using the MFT provided the conservation science community with robust data concerning the instrument, including new options for a more compact design (Lerwill et al. 2008;Lerwill 2012;Liang et al. 2011;Textile Specialty Group 2010). In 2010, the MFT was in use in 17 institutions worldwide (Whitmore & Tao 2010), mainly in conservation science labs. ...
The microfade tester is used to assess fading rates of fugitive colors of collection items. The paper presents the research considerations to design a simple, less expensive and portable contact microfade tester that could serve as a screening tool for conservators. Hardware design for such an instrument is presented that includes variations in light source (xenon or LED) and measuring head (ball lens or angled holder fiber), and does not need refocusing between measurements. Performance of the portable microfade tester versions was tested on lab samples and a paper based collection item and based on the ability to rank light sensitivity relative to that of ISO Blue Wool Standards 1, 2 or 3. The results are compared to the ranking obtained with the bench instrument when testing sensitivity of the same items for the same duration. All versions of the portable hardware were found suitable for use as a screening tool to discriminate light-sensitive collection items, with performance of the portable microfade testers using an LED optimized for samples more fugitive than Blue Wool Standard 3. These portable microfade testers need not replace the bench microfade tester as the presented portable microfade tester versions are only suitable to test collection items tolerating surface contact with the instrument.
... Another approach is to apply an objective means of assessing the light sensitivity of all the visually distinct colorants in a work of art, and to develop a display policy for each individual work based on the results (Ashley-Smith et al., 2002;Ford & Smith, 2011), which Tate is in process of doing . To this end, a microfadometer was developed by Whitmore et al. (1999Whitmore et al. ( , 2000 and Whitmore (2002) and has been improved, developed, and used by others worldwide (Ford, 2009;Druzik & Pesme, 2010;del Hoyo & Mecklenburg, 2011a, Liang et al., 2011, as well as being developed for improved portability and automated use as a screening device Lerwill, 2011) as will be described here. ...
An investigation for light exposure on pigments in low-oxygen environments (in the range 0-5% oxygen) was conducted using a purpose-built automated microfadometer for a large sample set including multiple samples of traditional watercolour pigments from nineteenth-century and twentieth-century sources, selected for concerns over their stability in anoxia. The pigments were prepared for usage in watercolour painting: ground and mixed in gum Arabic and applied to historically accurate gelatine glue-sized cotton and linen-based papers. Anoxia benefited many colorants and no colorant fared worse in anoxia than in air, with the exception of Prussian blue and Prussian green (which contains Prussian blue). A Prussian blue sampled from the studio materials of J.M.W. Turner (1775 - 1851) was microfaded in different environments (normal air (20.9% oxygen) 0, 1, 2, 3.5, or 5% oxygen in nitrogen) and the subsequent dark behaviour was measured. The behaviour of the sample (in normal air, anoxia, and 5% oxygen in nitrogen) proved to be consistent with the 55 separately sourced Prussian blue samples. When exposed to light in 5% oxygen in nitrogen, Prussian blue demonstrated the same light stability as in air (at approximately 21 degrees C and 1 atmosphere). Storage in 5% oxygen is proposed for 'anoxic' display of paper-based artworks that might contain Prussian blue, to protect this material while reducing light-induced damage to other components of a watercolour, including organic colorants and the paper support.
... In practice the drop in intensity is typically limited to about an order of magnitude by a combination of the fading rate of the colorant and instrument drift. However, Liang et al. (2011) were able to lower the effective detection limit to 1% of full power in some cases using an innovative automated recalibration process. Del Hoyo- Mendelez and Mecklenburg (2011) determined that for some very fugitive natural dyes demonstrating reciprocity over the first order of magnitude does not necessarily mean reciprocity holds at lower levels. ...
... This can affect results because rapid early fading tends to magnify differences that are not as apparent in the longer term. Whitmore et al. (1999) has published data for a few colorants that illustrate equivalence between microfading and conventional light box ageing as well as demonstrating reciprocity over the test intensities he used, and Liang et al. (2011) from Nottingham Trent University have found reciprocity held for a majority of painted-out samples on paper of fine art pigments tested, including some over two orders of magnitude, but the same team also reported reciprocity breakdown for the pigments Prussian blue and orpiment (Lange and Liang 2011). Del Hoyo-Mendelez and Mecklenburg (2011) found that the most stable colorants they tested obeyed reciprocity, but that materials of lower light-fastness exhibited greater apparent deviations. ...
... The relationship between colour change, which is an estimate based on models of how the ''average observer'' perceives reflectance differences resulting from pigment concentration changes (the physical reality), is complex and nonlinear. @ Liang et al. (2011) argue partly for this reason that spectral change in the absorption region (DR) is a better measure of sensitivity; however, the relationship between reflectance change and colorant concentration, described by the Kubelka Munk equations, is itself far from straightforward in real situations (JohnstonFeller 2001). Bacci et al. (2004) have shown that DE does not reflect photochemical damage as accurately as DR within the dominant absorption region, and it is possible to speculate that some apparent reciprocity deviations might even disappear if the latter were used. ...
Microfading ; is a powerful tool for assessing the risk of light damage in collections. It is an accelerated light exposure method for rapidly and nondestructively estimating the fading rates of colorants on real objects that relies on measuring the early response of a submillimetre spot of colorant exposed to megalux levels of light. While the main benefit is better identification and protection for the most light-sensitive elements of a collection, it has also been shown to have very significant access, financial, and operational benefits. The basic equipment is suitable for routine screening by a trained conservator in a museum. Alternatively many institutions' needs may be met using a contract service. This paper provides an up-to-date review of the technique's development, and how it is used as a tool for collection management and research.
