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The positive impact of daylight on various forms of life is well understood. The daylight conditions a person experiences inside a building strongly depend on the character of the glazing. Contemporary windows maximize the transmission of visible daylight. In post-medieval times glassmakers were confronted with less pure materials. Driven by the Reformation and Counter-Reformation they were at the same time challenged by the demand for increased daylight. Luckily, technological evolutions allowed the production of thinner windows. It is currently an open question if glassmakers in the (Southern) Low Countries during the booming economic period from the fifteenth to seventeenth century made use of the interplay between material and fabrication properties to bring light into the darkness. Therefore, this paper links the impact of glass purity and production technique to light transmission for a well-diagnosed group of excavated glass window pieces from the castle of Middelburg-in-Flanders and a set of roundels, all dating back to between the fifteenth and seventeenth centuries and explores what factors have influenced this technological improvement. A non-destructive approach making use of UV–vis–NIR absorption spectroscopy unveiled that the more recent material is less pure compared to the older dated material but that light transmission was maximized due to the applied production technique.

Size and concentration are two important parameters for the analysis of microplastics (MPs) in water. The analytical tools reported so far extract this information in a single-particle analysis mode, dramatically increasing the analysis time. Here, we present a combination of multi-angle static light scattering technique, called "Goniophotometry", with chemometric multivariate data processing for the batch analysis of size and concentration of MPs in water. Nine different sizes of polystyrene (PS) MPs with diameters between 500 nm and 20 mu m are investigated in two different scenarios with uniform (monodisperse) and non-uniform (polydisperse) size distribution of MPs, respectively. It is shown that Principal Component Analysis (PCA) can reveal the existing relationship between the scattering data of mono- and polydisperse samples according to the size distribution of MPs in mixtures. Therefore, a Linear Discriminant Analysis (LDA) model is constructed based on the PCA of scattering data of PS monodisperse samples and is subsequently employed to classify the size of MPs not only in unknown mono- and polydisperse PS samples, but also for other types of MPs such as Polyethylene (PE) and Polymethylmethacrylate (PMMA). When the size of MPs is classified, their concentration is measured using a simple linear fit. Finally, a Linear Least Square (LLS) model is used to evaluate the reproducibility of the measurements.

Carcinogenic contaminants in food are typically detected using sample-based and time-consuming chemical analysis. To offer a non-destructive alternative, we investigate the use of optical sensing methods for food safety evaluation, particularly considering broadband diffuse reflection spectroscopy and spatially resolved spectroscopy. As a case-study, the acrylamide sensing during potato processing is considered. For both spectroscopic methods, the broadband spectra (400-1700 nm) are recorded for different potato batches, showing acrylamide concentrations between 200 ppb and 2000 ppb, covering levels below and above the European regulation of 500 ppb. First, the raw spectra are evaluated enabling to identify the key spectral regions, being 400-525 nm, 750-1000 nm, 1220 nm, and 1440 nm, corresponding to different potato constituents such as riboflavin, starch, reducing sugar and water. Following, different data processing algorithms were applied maximizing the classification performance of the different batches. When considering the reflection spectroscopic data, a classification performance exceeding 92% could be obtained using Linear Discriminant Analysis, while with spatially resolved spectroscopy, a classification performance around 75% was obtained when considering the ratios of the diffuse and specular reflected light. Both techniques show a harvest-independent result, while coping with the large natural variation by considering the combined effect of different acrylamide precursors. In general, our results demonstrate that optical spectroscopy enables a successful acrylamide precursor sensing, allowing an accurate exclusion of potatoes unsuited for French fries production, complying with the European regulations.

Acrylamide formation is nowadays one of the major concerns of the potato-processing agriculture industry. We investigate the use of broadband reflection spectroscopy (400–1700 nm), in combination with machine learning, to optically classify raw potatoes inducing different levels of acrylamide after frying, covering concentrations between 200 ppb and 2000 ppb. Using the full spectral range, we obtain a correct classification of a dataset of 200 samples and using 10-fold cross-validation, while applying Linear Discriminant Analysis and Extreme Learning Machine. To reduce the amount of data and increase processing speeds, a sequential feature selection search was performed to identify the critical wavelengths (450 nm, 488 nm, 504 nm, 783 nm, 808 nm, 1310 nm, 1319 nm and 1342 nm) that enable classification performances exceeding 92% when applying Linear Discriminant Analysis. We therefore demonstrate a non-destructive identification of the potatoes unsuited for French fries production, enabling to increase food safety, while limiting food waste.

The early modern period is mainly characterised by High Lime-Low Alkali (HLLA) glass, a lime-rich glass made from plant or tree ashes, originating from 14th-century Germany and later used all over Europe. Attempts to link HLLA chemical subgroups to a particular point in time have failed so far. Driven by a request from the archaeological community, our research group has been exploring the feasibility of UV-Vis-NIR absorption spectroscopy as a non-destructive and in-situ applicable analysis technique for more than a decade. The main goal of this research is to provide a better understanding of the subgroups of HLLA glass and their respective dating via non-destructive means. A second topic relates to the role of cobalt as a potential indicator for either the type of applied ashes or for glass recycling. In this paper, we present the UV-Vis-NIR and LA-ICP-MS results of a total of 45 HLLA colourless glass objects or fragments, supplemented with three blue glasses from the 15th to the 17th centuries. First, we observed a correlation between iron and cobalt contents and that these two elements show more elevated concentrations starting from the middle of the 16th century. Different types of sources can be responsible, such as the type of raw materials, the tools employed, and recycling. We hypothesised that both elements were introduced through the wood or plant ashes used as fluxing agent. Then, we noted that the presence of low amounts of cobalt in colourless glass, can be observed through the analysis of the Co2+ absorption bands in the optical spectra down to 18 ppm. Next, we describe an approach to quantify iron and cobalt from the optical spectra and to date HLLA material by means of absorption spectroscopy, a valid, rapid, and non-destructive alternative for laboratory measurements. Finally, we show that the optical parameters (the Ultra-violet Absorption Edge (UVAE), the calculated Fe2+ and total iron contents, and the Co2+ absorption bands characteristics) allow discerning two glass groups: one dating to theend of the 15th-middle of the 16th centuries, and the other to the second half 16th-17th centuries. These results gain valuable information to further resolve the study on recycling, on the influence of the glassmaking tool on the glass batch composition and/or on the selection or treatment of the raw materials in HLLA glass.

Climate on Earth is determined by the Earth Radiation Budget (ERB), which quantifies the incoming and outgoing radiative energy fluxes at the top-of-atmosphere (TOA). The ERB can be monitored from space by non-scanning wide field-of-view radiometers (WFOV), or by scanning narrow field-of-view radiometers. Recently, WFOV radiometers have gained renewed interest as illustrated by the development of the RAVAN and SIMBA 3U CubeSats. RAVAN uses a Vertically Aligned Carbon Nanotubes (VACNT) coating, while the SIMBA CubeSat uses a novel cavity-based geometry with a Black Velvet coating. Both VACNT and Black Velvet are diffuse coatings, but when applied to flat sensors, the VACNT coating has a significantly lower reflectivity in comparison to classic diffuse or specular black coating materials. When used on a cavity radiometer, it is currently unclear if a VACNT coating would improve the measurement accuracy compared to other diffuse coatings, such as Black Velvet. In this paper, we therefore investigate the potential benefits of using the VACNT coating as an alternative for Black Velvet, in our in-house developed radiometer. Our analysis includes the evaluation of the influence of the cavity geometry as well as the coating absorption factor. The comparison of the VACNT with the Black Velvet coating is based on the absorption factor of the cavity that is determined using radiation view factor calculations. Scattering and stray-light analyses are carried out using commercially available ray-tracing software (ASAP®R, Breault Research). We evaluated whether the coating or the geometry is the main contributing factor to the performance of the radiometer. As a conclusion, we observed that for cavity-type radiometers, the difference in the cavity absorption factor between Black Velvet and VACNT becomes negligible, favoring the use of Black Velvet, since Black Velvet has a long space heritage and appears more user friendly from a fabrication point of view, as it can be deposited in an easier and more reproducible manner on the radiometer cavity walls, including non flat surfaces.

This paper critically compares the performance of four non-invasive techniques that match the accuracy, flexibility, time-efficiency, and transportability required for in situ characterization of leaded glass windows: macroscopic X-ray fluorescence imaging (MA-XRF), UV-Vis-NIR, Raman spectroscopy, and infrared thermography (IRT). In order to compare the techniques on equal grounds, all techniques were tested independently of each other by separate research groups on the same historical leaded window tentatively dated to the 17th century, without prior knowledge. The aim was to assess the ability of these techniques to document the conservation history of the window by classifying and grouping the colorless glass panes, based on differences in composition. IRT, MA-XRF and UV-Vis-NIR spectroscopy positively distinguished at least two glass groups, with MA-XRF providing the most detailed chemical information. In particular, based on the ratio between the network modifier (K) and network stabilizer (Ca) and on the level of colorants and decolorizers (Fe, Mn, As), the number of plausible glass families could be strongly reduced. In addition, UV-Vis-NIR detected cobalt at ppm level and gave more specific information on the chromophore Fe2+/Fe(3+)ratio. Raman spectroscopy was hampered by fluorescence caused by the metal ions of the decolorizer in most of the panes, but nevertheless identified one group as HLLA.

Roman glass is studied here by means of optical absorption spectroscopy, in order to provide an objective method to quantitatively evaluate colour. The dataset is composed of 165 soda-lime silicate glass samples from various western European sites, mainly dated from the first to fourth century AD, and containing variable amounts of iron, manganese and/or antimony. Iron redox ratios and colour coordinates (based on the CIELab colour system) are determined and put in relation with the thickness of samples and their manganese/antimony contents. Results reveal thickness as a crucial parameter when discussing glass hues, thus leading to a differentiation between the ‘intrinsic’ and ‘perceived’ colour of glass objects (i.e. the colour of the object with the thickness normalised to 1 mm, and that with its original thickness, respectively). Apart from HIMT and purple glass, the concentration of ferrous iron appears to be correlated with a* — a colourimetric parameter determining how green the glass is. Significant relations of antimony/manganese contents versus iron redox and glass colour are also considered, resulting in quantitative arguments to entitle antimony-decoloured glass as the most oxidised and colourless glass., SCOPUS: ar.j, info:eu-repo/semantics/published

We propose a semianalytical method to model, in both two and three dimensions (2D and 3D, respectively), the radiation emission of quantum emitters (QEs) interacting with nanopatterned structures. We then investigate the emission from QEs near a hyperbolic metamaterial (HMM) with a metallic cylindrical grating on its top and a poly(methyl methacrylate) substrate embedded with QEs on its bottom. The optimization of the cylindrical grating is carried out first using a 2D model (due to its low computational cost), followed by a performance study based on a 3D model. We show that an appropriate choice of grating parameters (period, height, and fill factor) allows not only the control of the QE emission direction but also the increase of both the Purcell factor and the total power coupled from the HMM into free space. In addition, the proposed method provides a detailed mapping of both the Purcell factor and the radiated power as a function of position, enabling us to understand how the QE location affects its behavior. Furthermore, we demonstrate that the QEs with the highest Purcell factor (viz., perpendicularly polarized ones) contribute more to the power radiated into the far field than previously expected. We also show that, in addition to a high Purcell factor of about 145, perpendicularly polarized QEs radiate up to 2 times more power if placed 10 nm from the HMM as they would in free space.

Quantitative analysis of size and concentration of microplastics is a crucial step for having a better understanding of plastic pollution in the environment. Such information is typically obtained in a single particle mode that significantly increases the analysis time and can be a cumbersome task. Therefore, we demonstrate here a measurement technique based on Static Light Scattering (SLS) combined with chemometric methods such as Principal Component Analysis (PCA) and Linear Discriminant Analysis (LDA) for resolving the size and concentration of multiple microplastic particles in water. Two sets of samples with uniform and non-uniform size distribution of microplastics, called “monodisperse” and “polydisperse”, respectively, are fully investigated. It is shown that a relationship exists between the scattering signals of mono- and polydisperse samples on the PCA space. Hence, a PCA-LDA model that is constructed on the PCA space of monodisperse samples is used to discriminate the size of the microplastics in polydisperse samples. By specifying the size of the particles, their concentration is determined using a simple linear fit.

Earlier research has shown that several common late antique glass types circulate in Cyprus between the fifth and the seventh century AD, specifically Levantine 1, HLIMT, HIMTa, HIMTb and Egypt 1, HIT, Roman and a plant ash glass. By investigating the glass material from Yeroskipou-Agioi Pente, Maroni-Petrera, and Kalavasos-Kopetra, we aimed to refine the chemical groups present within three late antique Cypriot sites and define the relations between trace elements obtained from LA-ICP-MS. Our data demonstrate compositional patterns that can be exploited to provenance late antique glass by investigating the REE-bearing mineral fractions, the amount of zircon and the carbonaceous fraction of the sand. In addition, Nb and Ti display a strong linear relation which depends on the glass type. Finally, the paper discusses the occurrence of glass recycling on the island and how this activity influenced the concentration levels of specific trace elements. Our study thus sets out an analytical framework to identify recycling events tailored on each compositional type.

Food quality and food safety are gaining more and more importance in recent decades. In particular, applications have included domains such as the identification of foreign bodies in solid food streams, the quality screening of vegetables and fruits, the recognition of food products inducing a health risk and the monitoring of the quality and authentication of liquids. Solid food sensing methods are often insufficient in the sense that they are error-sensitive and time-consuming due to the manual or chemical, samplebased screening of the products. For most liquids a decent monitoring method is missing. In view of this, the authors of these papers started exploring the potential of photonics to answer the question if food screening methods could be photonics- based. This paper gives an overview of our research of the past eighteen years.

In this paper we have studied by optical spectroscopy the 5th–7th century glass material from three early Christian sites in Cyprus: Yeroskipou, Maroni Petrera and Kalavasos Kopetra . The glasses could be grouped into six chemical types: Levantine 1, HLIMT, two types of HIMT (named HIMTa and HIMTb), Egypt 1 and HIT. This work presents the first extensive application of in situ absorption spectroscopy to ancient glasses. UV absorption edge, Fe 2 + concentration and colour coordinates are optical parameters that help identifying glass composition because there exists a link between chemical groups and UV–vis–NIR spectral shapes. This allows to select samples for chemical analysis on the basis of diverging optical properties rather than using ad random or subjective naked-eye strategies groups. Furthermore, optical spectroscopy offers an insight into the redox conditions under which the glasses were melted. We also show why the common practice among glass archaeologists to associate certain colour to specific chemical compositions can lead to misinterpretation of the glass consumption.

At the beginning of the 20th century, the application of innovative finishes on facades became a popular phenomenon in Belgium. Decorative renders were frequently used to hide the aesthetically imperfect structure and to imitate valuable natural stone features. In order to create the appearance of French stone, ingredients such as lime, mica and crushed natural stone were added to white cement. Afterwards, the surface was scratched or scraped to shape a rough texture. As a result, a convincing ‘simili-pierre’ or ‘stone imitation’ masonry was obtained, after drawing simulated joints into the wet render layer. Today, these imitation finishes suffer in most cases from discoloration, cracks, peeling off and other damage which has completely changed the initial perception. Since knowledge is lacking concerning their composition, properties and application techniques, many questions remain unanswered within the conservation area. As a consequence, incorrect decisions may be made during restoration campaigns, which may lead to additional damages. A remarkable example of a simili-pierre render is the former commercial product Terranova, which is the focus of the research. By means of literature studies, the exploration of historical patents, laboratory analysis of representative samples and a comparative research between similar claddings, this paper proposes legitimate solutions to revitalize the Terranova finishes. It is found that both original mortar formulas and historic application guidelines are key elements which form a fundamental contribution to restore stone imitating renderwork in a sustainable way, with respect for authenticity issues.

Optical laser-scanning systems generally contain a scanning lens, like an f-Theta lens, to enable a planar imaging field. However, commercially available f-Theta lenses show limited working distances and scan fields, while their lens diameter rapidly scales with the scanning range giving rise to bulky lens systems. Therefore, we propose a novel scanning lens configuration, based on a compact tunable lens system, generating a planar imaging field within scanning configurations that require broad scanning fields at large working distances. Particularly, we developed a refocusing illumination lens system, comprising a voltage tunable liquid lens positioned in the centre between 2 passive aspherical lenses. Our novel developed optical system is implementable between the laser source and scanning mirror in a polygon laser-scanning system and ensures a constant spot size along a 640 mm scanning line at a working distance of 900 mm. The voltage tunable liquid lens (Arctic 316 lens of Varioptic) enables to adapt the focal length by the application of a voltage, while the passive aspherical lenses allow to enlarge the working distances and to correct for aberrations. We obtained a compact lens system (system length of 71.8 mm) showing a tunable back focal length between 1078 mm and 1134 mm and 1/e 2 spot diameters between 229 μm and 238 μm along the scanning line. Furthermore, we successfully demonstrate the performance of our simulated advanced refocusing illumination system in a laser-based scanning configuration, indicating its potential for integration in industrial scanning systems operating at large working distances while requiring large scanning fields.

Insulating heritage buildings in order to provide a comfortable indoor climate, to reduce energy consumption and avoid thermal stresses into the structure, is generally not in accordance with architectural preservation guidelines. Without compromising historic features, insulation renders may however upgrade rendered heritage of which the original materiality is considered inferior compared to its design. This study evaluates the hygrothermal performance of 49 insulating lime-perlite render configurations on brick masonry, by combining characterisation experiments with numerical modelling. The effects of the coupled heat-moisture transport are finally validated by ageing cycles and bond strength tests. It is found that insulating renders cause smaller shifts in temperature in the structure compared to historic renders, but the moisture level of the support may increase significantly. In addition, the insulation layers store a lot of moisture during winter, affecting the expected insulation capacity. (C) 2017 Elsevier Ltd. All rights reserved.

Scientific analyses of ancient glasses have been carried out for many years using elemental chemical analysis. However, it is known that the control of the redox conditions in the glass melt has a strong implication on the final hue of glass because it affects Fe2+/SFe. Therefore an increasing number of studies on the redox conditions have been published in recent years by means of synchrotron based Xray absorption spectroscopy. This is a technique which is not easily accessible and requires dedicated facilities. In this paper we describe an alternative approach by means of optical absorption spectroscopy. We synthesised 10 soda-lime-silica glasses with known redox conditions and iron concentration to calibrate the absorption at 1100 nm as a function of Fe2+ concentration. The linear extinction coefficient was also determined. These glasses were also studied by means of X-ray Absorption Near Edge Structure (XANES) spectroscopy. Electron paramagnetic resonance spectroscopy was additionally used as an ancillary method to verify the quality of our data. Furthermore 28 samples from real archaeological samples were analysed by XANES and optical spectroscopy as a case study. The Fe2+/SFe values obtained were compared and demonstrated that the two techniques were in good agreement with each other. Optical spectroscopy can be applied in situ with moderate sample preparation to determine the concentration of Fe2+. To investigate the redox conditions, especially as a first screening approach, this methodology is an important tool to take into consideration before applying more sophisticated techniques such as XANES, which is more elaborate and requires high-tech resources.

The formation of acrylamide during the frying of potatoes is nowadays one of the major concerns of the potato-processing agriculture industry. Much research has been carried out to identify the acrylamide precursors in raw potatoes in order to minimize its formation during frying. Raw potatoes that give rise to an excess of acrylamide can currently not be detected in a fast, sensitive and non-destructive way. Therefore, we investigate the use of spatially-resolved spectroscopy to optically identify raw potatoes with high acrylamide precursors concentrations, on basis of their internal scattering properties. To obtain potatoes that induce high acrylamide concentrations, we stored the potatoes in a fridge at 4 °C. Measurements of the potatoes after different storage times (11, 15, 21 and 28 weeks), corresponding with different acrylamide concentrations in the French fries, show an evolution of the scatter pattern. Furthermore, when comparing the scatter properties at different wavelengths for potatoes giving rise to low (600 ppb) acrylamide concentrations during frying, an optimized classification of the potato batches was obtained at 1444 nm. We can conclude that the internal scatter properties of peeled, raw potatoes can be used to monitor the acrylamide precursors, enabling a non-destructive exclusion of the potatoes that are not suited for French fries production.

Nanopatterned hyperbolic metamaterials (NPHMs) have proven to be efficient structures for enhancing the spontaneous emission rate (Gamma) and quantum efficiency (eta) of quantum emitters (QEs). However, many of the NPHM designs still rely on computationally costly 3D numerical simulations. In this context, we propose a fast, semi-analytical method capable of calculating both Gamma and eta of QEs placed inside a medium bounded by nanopatterned structures. The low computational cost of our approach makes it attractive for optimizing the NPHMs' geometrical parameters that maximize eta for a desired Gamma. Furthermore, we suggest a more realistic procedure to calculate the decay behavior of multiple QEs arbitrarily distributed in the NPHM. This calculation is only feasible with the knowledge of Gamma and eta mapped for all possible positions of the QEs, which is easily achieved with the proposed model. For the validation procedure, we compare the model results with those obtained by the FDTD method. We apply the proposed model to an NPHM composed of nine Ag/SiO2 layers, with the polymer host layer embedded with rhodamine 6G, to maximize eta for a specified tenfold increase of Gamma. This procedure allowed eta to be increased by 69% and 170% for 1D and 2D nanopatterning, respectively. The time required to build the Gamma and eta maps (used in the calculation of the decay behavior) is reduced by approximately 96% when compared with those numerically calculated via FDTD. (C) 2019 Optical Society of America

Deoxynivalenol is one of the most abundant contaminants in crops worldwide. Its presence in food and feed products causes health risks and induces economic losses. To date, deoxynivalenol is mostly detected by sample-based, time-consuming chemical analyses. To obtain a non-destructive detection of deoxynivalenol in unprocessed, solid maize kernels, we investigate UV-Vis-NIR diffuse reflection spectroscopy. Specifically, we propose a two-stage spectroscopic measurement procedure, allowing the characterization and identification of deoxynivalenol in ungrounded maize kernels. The first stage focuses on the characterization of the optimum illumination and detection wavelengths, by the measurement of the mean contamination of a collection of maize kernels, using a 250 mm-reflection integrating sphere. The second measurement stage enables an accurate clasification of contaminated maize grains, by the measurement of the local contamination on individual kernels,, using a 30 mm reflection integrating sphere. We firstcharacterized and compared the reflection spectra of low (150 ppb) and high (1388 ppb) natural deoxynivalenol-contaminated maize kernels. Moreover, we validated these measurement results by the characterization of a reference deoxynivalenol-contaminated maize powder (1840 +/- 30 ppb). A spectral contrast between the low and high contaminated samples could be observed between 700 nm and 1400 nm. Furthermore, a detection criterion could be defined, allowing us to successfully classify a contaminated maize batch into a high (18184 ppb) and low (654 ppb) contaminated subsample. As a result, this verifies the two-stage measurement approach and illustrates the use of diffuse reflection spectroscopy as a valuable tool for the measurement of deoxynivalenol concentrations in maize, paving the way for real-time non-destructive industrial scanning-based detection. (C) 2016 Elsevier Ltd. All rights reserved.

Civilized societies should safeguard their heritage as it plays an important role in community building. Moreover, past technologies often inspire new technology. Authenticity is besides conservation and restoration a key aspect in preserving our past, for example in museums when exposing showpieces. The classification of being authentic relies on an interdisciplinary approach integrating art historical and archaeological research complemented with applied research. In recent decades analytical dating tools are based on determining the raw materials used. However, the traditional applied non-portable, chemical techniques are destructive and time-consuming. Since museums oftentimes only consent to research actions which are completely non-destructive, optical spectroscopy might offer a solution. As a case-study we apply this technique on two stained glass panels for which the 14th century dating is nowadays questioned. With this research we were able to identify how simultaneous mapping of spectral signatures measured with a low cost optical spectrum analyser unveils information regarding the production period. The significance of this research extends beyond the re-dating of these panels to the 19th century as it provides an instant tool enabling immediate answering authenticity questions during the conservation process of stained glass, thereby providing the necessary data for solving deontological questions about heritage preservation.

The presence of mycotoxins in food products is a major worldwide problem. Nowadays, mycotoxins can only be detected by the use of sample-based chemical analyses. Therefore, we demonstrate the use of one-and two-photon-induced fluorescence spectroscopy for the non-destructive detection of mycotoxins in unprocessed food products. We first explain our optical set-up, which is able to measure the localized one-and two-photon-induced fluorescence spectra. Following, as a case study, the detection of aflatoxin in maize kernels is discussed. We present our research methodology, from the characterization of the fluorescence of pure aflatoxin, to the study of the one- and two- photon-induced fluorescence spectra of maize kernels and the development of an optical detection criterion. During both one- and two-photon-induced fluorescence processes, the fluorescence of the aflatoxin influences the intrinsic fluorescence of the maize. Based on the fluorescence spectrum between 400 and 550 nm, a detection criterion to sense the contaminated kernels is defined. Furthermore, we successfully monitored the localized contamination level on the kernel’s surface, showing both contaminated kernels with a high contamination in a limited surface area (a few square millimetres) and kernels with a low contamination spread over a large surface area (up to 20 mm2). Finally, the extensibility of our research methodology to other fluorescent mycotoxins is discussed.

The presence of carcinogenic aflatoxins in food and feed products is a major worldwide problem. To date, the aflatoxin contamination can only be detected by the use of destructive sample-based chemical analyses. Therefore, we developed an optical setup able to detect the localized aflatoxin contamination in individual maize kernels, on the basis of one-and two-photon induced fluorescence spectroscopy. Our developed optical configuration comprises a tunable titanium-sapphire laser (710nm-830nm) in combination with second harmonic wavelength generation (355nm-415nm), enabling the measurement of both one-and two-photon induced fluorescence spectra. Moreover, an accurate scanning of the kernel's surface was induced by the use of automated translation stages, allowing to study the localized maize contamination. First, the operation of the setup is validated by the characterization of pure aflatoxin B1 powder. Second, the fluorescence spectra of healthy (< 1ppb aflatoxin B1) and contaminated maize kernels (> 70ppb aflatoxin B1) were measured, after excitation with 365nm, 730nm, 750nm and 780nm. For both the one-and two-photon induced fluorescence processes, the presence of the aflatoxin inside the contaminated maize kernels influenced the intrinsic fluorescence signals. Based on the fluorescence spectrum between 400nm and 550nm, we defined a detection criterion to identify the contaminated maize kernels. Furthermore, we demonstrate the sensing of the localized contamination level, indicating both contaminated maize kernels with a high contamination level in a limited surface area (as small as 1mm(2)) as with a lower contamination spread over a large surface area (up to 20mm(2)). As a result, our developed measurement methodology allows the identification of the localized aflatoxin contamination, paving the way to the non-destructive, real-time and high-sensitive industrial scanning-based detection of aflatoxins in food products.

The main purpose of this publication is to define sensing parameters by means of optical spectroscopy to study and characterize ancient glass. Because during different times different flux agents were used, a chemical individuation of these elements provides a first dating classification. Normally, X-ray-based chemical methods are applied to this kind of investigation. On the basis of the Ligand-field theory, the absorption band positions of a transition metal ion undergo a change when the ion is placed in different chemical environments. A total of 25 cobalt coloured Roman, post-medieval and industrial glasses were analyzed by means of SEM–energy dispersive X-ray spectroscopy to group them according to their chemical composition. Optical spectroscopy was applied to build a method to study glass with this low-cost and nondestructive technique. It is proved that the cobalt absorption band situated around 535.5 nm for sodium-rich glasses (Roman and industrial material) is shifted towards 526.5 nm for calcium–potassium-rich glasses (post-medieval window glass). This feature was employed as a marker in the case study of the Renaissance window of the Church Wardens from the Church of Our Lady in Bruges, Belgium to distinguish the post-medieval material from the 19th and 20th century restoration material. Copyright # 2011 John Wiley & Sons, Ltd.

Raman spectroscopy has been used to identify iron-containing glasses. This nondestructive technique offers a fast method to obtain qualitative information about the presence of iron oxides in glass. The effect of the iron content in glass samples is reflected on the topology of the Raman spectra: A strong link between the ratio of the Q2/Q3 vibration units of the silica tetrahedral structure is seen. If matrix effects are taken into account, also (semi)quantitative results can be obtained from the calibration lines. The linear calibration is based on the normalized band intensity at 980 cm −1 (I980/I1090 )a nd the iron oxide concentration for similar glasses. In amber and dark colored glasses, an extra peak in the spectrum indicates the presence of a FeS chromophore. Different series of glasses of various origins (ancient and modern/industrial glass) have been considered. Copyright c � 2011 John Wiley & Sons, Ltd.

The aim of this paper is to highlight the potential of Raman spectroscopy as a fast screening method for large amounts of glass samples. Besides the dedicated research of specific glass collections during the last ten years, a broad corpus of archaeological window glass still needs to be investigated. For many sites, the amount of excavated glass artefacts is enormous and a selection of the most appropriate samples for chemical analysis is necessary. A classification can be made on the basis of the typical Raman signatures for the different kinds of glasses (alkali glass, high-lime low-alkali (HLLA) glass, Pb-rich glass). Even in case of strong fluorescence, an uncomplicated treatment (normalisation) of the measured signals makes it possible to distinguish between the different types of glass. The preliminary screening of glass artefacts with Raman spectroscopy is a useful tool in the study of historical glass and can already answer some questions about provenance, period of production and authenticity of the glass samples. Copyright © 2010 John Wiley & Sons, Ltd.

This paper discusses the composition of the vessel and window glass from three Late Antique Cypriot sites: Yeroskipou, Maroni-Petrera and Kalavasos-Kopetra. Over 170 glass fragments were sampled for quantitative chemical analysis through EPMA measurements. The aim of this work is to establish new insights on the chemical compositions of the glass from Late Antique Cypriot sites to observe the distribution of glass on the island. Furthermore, we compare our dataset with published data of contemporary materials from other regions. Four compositional groups were recognized and correlated to known chemical compositions: Levantine 1, Egypt 1, two types of HIMT glass, HIMTa and HIMTb, while a new group, High Lime Iron Manganese Titanium (HLIMT) has been defined. Glass was supplied to Cypriot glassmakers by both Egyptian and Syro-Palestinian primary producers. Nevertheless, we have observed a specific distribution pattern on the island. In the west, there is about 50:50 ratio between Levantine and Egyptian suppliers. On the contrary, in the central south coast the amount of Egyptian glass drops consistently, in particular in Kalavasos, leaving space to Levantine glass. (C) 2015 Elsevier Ltd. All rights reserved.

In the late 19th century, the introduction of Portland cement and understanding of hydraulic binders led to innovative compositions towards decorative finishing materials. To avoid grey and dull cement appearances, craftsmen started to manipulate the mortar mixtures by adding mineral particles and pigments, creating a material resembling a particular natural stone. Such a stone imitation could be applied as a render layer on facades or implemented in walls as brick elements, which are respectively known as ‘simili-plaster’ and ‘artificial stone blocks’. Both techniques were developed as a substitute for the more expensive quarried natural stones, like marble, sandstone and limestone when they were locally not available. Apart from the existence of a few commercialized ready-mix imitation renders, we do not know a lot about the technological evolution of the Belgian stone imitation industry. This knowledge is essential for historical preservation, since these materials were extensively applied in facades during the interwar period and today more and more young heritage needs to be restored. Therefore, the aim of this research was to gain knowledge on the development of these popular artificial stone claddings with an important focus on their manufacturing process. By studying patents requested between 1880 and 1940 in Belgium, original mortar compositions could be determined, and a quantitative analysis sheds light on their glory days and the degree of knowledge transfer from neighboring countries.

The present research evaluates damage problems of historic stone imitating renders. Such decorative mortars were applied on façades to create the illusion of a French sandstone or limestone masonry. Visual analysis of three listed case studies from the early 20th century sheds light on the lifespan of these materials by assessing their characteristic damage patterns and helps to understand the causes of their degradation. Soiling, cracks, adhesion problems, biological growth and surface erosion are observed and discussed. Although the renders are in relatively good condition, discolorations disrupt the monumental value and deterioration often increases after improper conservation interventions.

In the late 19th century, the introduction of Portland cement led to innovative compositions towards decorative rendering mortars. These finishes were often developed as a substitute for other, more expensive materials, like sandstone. In order to create an almost perfect imitation of a natural stone masonry, imitation renders were frequently applied on façades. After roughening the texture, simulated joints were drawn into the wet surface. These artisanal imitation mortars were prepared on site by craftsmen, according to their own formula and skills. Generally such mortars contained lime, white cement, crushed stone and mica particles. Due to variations in composition and application technique, almost none of these façade finishes had an identical appearance. According to Belgian architectural periodicals and plasterer's manuals (1900-1940), ready-mix mortars gained popularity after World War I. Adding water to these dry prefabricated mixtures resulted in a uniform stone-like surface, which met the standard requirements. This paper sheds light on successfully imported foreign ready-mix mortars, such as Terranova, but also on innovative Belgian renders like Dura and Supra. Knowledge of how these stone imitating renders have been used, manufactured, mixed and applied is essential to propose viable restoration strategies. By means of written historic sources such as journals, patents, manuals and advertisements, this paper will focus on the technical aspects of the mentioned ready-mix renders and their related socio-cultural background.

When restoring decorative mortar layers on historic façades, professionals need to determine the colour of these finishes in order to select an appropriate repair mortar. Currently, the appearance of these renders is only assessed from a subjective point of view. To match with the aesthetic aspects of the façade, contractors must constantly adjust their repair mortar composition to avoid a patchwork of different colours, which is detrimental for heritage. This time-consuming (trial-and-error) methodology can be excluded by evaluating 'colour' with an objective numerical approach. The challenge of the research was to define and evaluate optimal material dependent boundary conditions for measuring the colour of nonhomogeneous mortars. Four samples with different scale of heterogeneity were measured by two spectrocolorimeters, both with a diffuse illumination geometry. The results were plotted in CIE-L*a*b* colour space. By calculating the colour difference (Delta E*), the influence of measuring with or without specular component was evaluated. We discovered the minimal number of measuring points depends on the scale of heterogeneity and the aperture area. The less homogeneous the mortar sample is and the smaller the aperture area, the more unique measuring points are required. Therefore, it is recommended to choose an aperture head of 25 mm or more to reduce the number of measurements, making your work time-efficient. However, in order to obtain accurate measurements on site, a portable optical spectrum analyser can be used with a 6 mm-diameter aperture, a viewing angle of 10°, SCI mode, illumination source D65, considering a minimum of 15 unique measuring points.

We studied the Fe K-edge X-ray absorption near edge (XANES) spectra of several Roman black glass fragments in order to determine the Fe3+/Sigma Fe ratio of these materials. The selected archaeological glass samples cover the period 1st-5th century AD in nine different sites of the North Western provinces of the Roman Empire. The fragments belong to two different compositional groups demonstrating a diachronic evolution: early Roman HMG (High Magnesia Glass) and Roman Imperial LMG (Low Magnesia Glass). The first group contains natural Fe levels (below 2 wt% as Fe2O3), while the LMG has concentrations above 5 wt%. This difference is also reflected by Fe3+/Sigma Fe values. Low iron glass was produced under strongly reducing conditions in order to obtain the black colour, with average Fe3+/Sigma Fe values approximate to 0.17. LMG glass is somewhat more oxidised (Fe3+/Sigma Fe approximate to 0.4-0.5). While HMG glass required active control of the furnace environment, LMG was made under ambient atmosphere and its higher oxidation degree is mainly determined by the chemistry of the raw glass.

The aim of the research was to observe and to analyse the repair procedure of a listed façade from the interwar period, finished with a stone-imitating mortar layer. Many theoretical studies have been published about the most diverse aspects of repair mortars for historic buildings, but it is important to know how many of these findings are already implemented in daily restoration practice. Starting from the initial condition, damage typologies were located on the façade surface and linked to their corresponding causes. Subsequently, a specialized contractor was appointed for the restoration process. After cleaning the façade with a soft wet sandblasting method (Torbo) and removal of damaged mortar segments, two repair mortars were applied. A structural repair mortar was attached to the masonry substrate and on the other hand a mixture of commercial mortar powders was used to obtain an imitative top finish. Finally, the used finishing techniques, such as the scratching, simulation of joints and the treatment of ornaments, are discussed and evaluated.

Raman spectroscopy is presented as a suitable and fast non-destructive technique to obtain qualitative information about glass samples of various origins (ancient and modern/industrial glass). A first application is the broad corpus of archaeological window glass that still needs to be investigated. For many sites, archaeologists have to deal with large collections of excavated glass samples and a selection of the most appropriate samples for chemical analysis is necessary. A fast classification can be made based on Raman spectra: different kind of glasses (Alkali-glass, High Lime-Low Alkali glass (HLLA)) have their own typical Raman signature. Even for glasses giving strong fluorescence, a classification is possible after a simple treatment of the Raman data. Raman spectroscopy has also been utilized to identify iron containing glasses. The effect of the iron content in glass samples is reflected on the topology of the Raman spectra: a strong link between the ratio of the Q2/Q3 vibration units of the silica tetrahedral structure is seen. Even (semi-) quantitative results can be determined from calibration lines if matrix effects are taken into account (similar glasses). In amber colored glasses, an extra peak ~415cm-1 in the Raman spectra indicates the presence of a Fe-S chromophore. Finally, in the fluorescent signals of some yellow and red glasses two peaks of Zn-Se-Cd-S nanocrystals have been identified.

Absorption spectroscopy is the technique that measures the absorption of radiation as a function of wavelength, due to its interaction with the material. During a research project funded by our home university, we were able to investigate the possibilities of this technique to study ancient glasses. One of our main conclusions is that UV-VIS-NIR absorption spectroscopy is especially suited to characterize colored artifacts in terms of composition and furnace conditions. Moreover, for naturally colored window glasses, we have shown that this technique allows us to classify fragments based on differences in iron impurity levels. It is a semi-quantitative analysis tool that can be applied for a first-line analysis of (large) glass collections. Thanks to the commercial available portable instruments, these measurements can be performed at relative high speed and this in-situ if necessary. To illustrate the possibilities of this technique, we describe in this paper two case-studies. In a first test-case we analyze 63 naturally colored window glasses and demonstrate how groups with different iron concentrations can be identified by calculating the absorption edge position from the measured optical spectrum. In a second case-study 8 modern naturally colored and 31 intentionally colored Roman glass fragments are the point of focus. For these samples we first estimate which samples are potentially fabricated under the same furnace conditions. This is done based on the calculated color values. Finally we identify the type of applied colorants.

In this paper we studied the transmittance spectra of a collection of several glass samples taken from a 16th century stained window of the Church of Our Lady in Bruges, Belgium. We recorded the optical spectra for all the samples in the region between 350 and 1600 nm. The goal of our research was to reveal information about the composition of the glass artifacts in a fast and non-destructive way. Analysis of the optical spectra allowed us in the first place to identify the type of colorants that were used. It was possible to recognize metal ions, such as Fe 2+ , Fe 3+ , Co 2+ , Mn 3+ , Cr 3+ and Cu 2+ . Also colors made of metal nanoparticles, such as silver and copper colloids were successfully identified. The recognition of the coloring agents is of particular interest in dating the glass pieces. This is because some colorants were only used in certain periods. Green glass colored by chromium was produced only after the mid 19th century onwards. Our study showed that 3 of the 10 pieces were colored by this element and they originate as such from a later period. A second conclusion refers to the applied fluxing agent. By analyzing the spectral position of the first cobalt absorption band, we were able to classify the glass pieces as potash based (used in medieval times) or soda-based (used in modern times) and therefore to classify them as original or as restoration material. From the 10 blue colored samples, 7 of them were recognized as original material. Finally, for the naturally colored parts the analysis of the spectra allowed us to group them based on cobalt impurities.

The propagation of coherent light through a heterogeneous medium is an often-encountered problem in optics. Analytical solutions, found by solving the appropriate differential equations, usually only exist for simplified and idealized situations limiting their accuracy and applicability. A widely used approach is the Beam Propagation Method in which the electric field is determined by solving the wave equation numerically, making the method time-consuming, a drawback exacerbated by the heterogeneity of the medium. In this work we propose an alternative approach which combines, in an iterative way, optical ray-tracing simulation in the software ASAP™ with numerical simulations in Matlab in order to model the change in light distribution in a medium with anisotropic absorption, exposed to partially coherent light with high irradiance. The medium under study is a photosensitive polymer in which photochemical reactions cause the local absorption to change as a function of the local light fluence. Under continuous illumination, this results in time-varying light distributions throughout the irradiance process. In our model the fluence-absorption interaction is modelled by splitting up each iteration step into two parts. In the first part the optical ray-tracing software determines the new light distribution in the medium using the absorption from the previous iteration step. In the second part, using the new light distribution, the new absorption coefficients are calculated and expressed as a set of polynomials. The evolution of the light distribution and absorption is presented and the change in total transmission is compared with experiments.

In this paper we studied the reflectance spectra of different green vegetables. The main objective was to identify the wavelength(s)(areas) that are the most sensitive to variations in pigment composition. With this we try to meet the ever growing demand from society to classify food products on their quality which is related to the state of ripening and degradation. The group of investigated samples consisted of a group of seven different green vegetables. Because these products have different pigment compositions they formed the ideal test samples for our research. For each product type we measured the reflectance spectra between 400 and 800 nm for 30 samples. From these spectra we investigated three different types of measurands: the measurands that are nowadays commonly used to monitor color differences, the vegetation indices that are defined to monitor plant leaves and measurands that are taking into account the entire reflectance spectrum in the visible part of the electromagnetic spectrum. The main conclusion of our research was that a combination of the first two mentioned types of indices allowed us to identify the different product groups in an optical way.