UV Fluorescence Research Articles

Yellow fluorescent UV-curable epoxy acrylate/VTMS-modified GQDs coatings: study of UV-blocking and viscoelastic properties

Polymer coatings decompose in the presence of UV radiation from sunlight and beget economic and environmental losses. Hence, it is necessary to reinforce the polymer coatings with UV-blocking nanoparticles and to convert the UV light into visible light. In this research work, the surface of graphene quantum dots (GQDs) was modified by vinyltrimethoxysilane (VTMS). VTMS-modified GQDs (VmGQDs) including 0, 0.3 and 0.6 wt% were taken into account to synthesize UV-curable epoxy acrylate/VmGQDs (Ep/VmGQDs) nanocomposite coatings. Surface modification, UV-blockage, fluorescence features and viscoelastic properties of Ep/VmGQDs coatings were analyzed by various spectrometry tests. The existence of VmGQDs (0.3 wt% and 0.6 wt%) in the polymer matrix led to absorption of UV rays in UV regions and fluorescence emission in the visible area with 578 nm wavelength (yellow fluorescence). Appearance of strong absorption bands at 250, 285 and 365 nm by the coatings with VmGQDs confirmed that a large portion of UV rays was absorbed and blocked. The intensity of UV-blockage by Ep/VmGQDs 0.6 wt% was recorded >99%. Furthermore, reinforcement of the coatings with VmGQDs resulted in increase in storage modulus, cross-linking density and Tg value.

Green synthesis of ZnO nanoparticles: in-silico and in-vitro assessment of anticancer and antibacterial activity and biomolecule (DNA) binding analysis

The zinc oxide nanoparticles (ZnO NPs) were synthesized by a green chemistry approach utilizing Stachys schtschegleevii Sosn.) S. schtchegleevii (extract, aims to innovate by employing environmentally friendly techniques. The production of ZnO NPs was confirmed by FT-IR, zeta potential, TEM, SEM-EDX, DLS and ultraviolet-visible techniques. The antibacterial potency of the ZnO NPs was evaluated toward pathogenic strains of E. coli and S. aureus. The antibacterial efficacy of this NPs against the selected bacteria followed the sequence: S. aureus > E. coli. The results of the MTT assay indicate that ZnO NPs have significant anticancer potential against the MCF-7 cell line. Furthermore, the synthesized ZnO NPs demonstrate a stronger inhibitory effect compared to the extract on the cancer cell line. To find out the potential of ZnO NPs as therapeutics, interaction process with calf-thymus DNA (ct-DNA) was performed by using absorption, and fluorescence studies. The evaluation of the fluorescence spectra and UV–visible absorption showed a satisfactory association of the ZnO NPs with ct-DNA. Besides, to clarify the binding interactions of ZnO NPs with the enzymes and ct-DNA, molecular docking simulation was performed. The molecular docking’ results show a well compromise with our experimental results. In total, the present investigation employs ZnO NPs synthesized through green methods as an efficient strategy for the purpose of the potentiation of anticancer and antibacterial activities in a biocompatible manner.

Ozone-microbubble-enhanced oxidation of pharmaceuticals and personal care products in municipal secondary effluents

Microbubble aeration can greatly improve ozonation by enhancing ozone transfer and subsequent hydroxyl radical formation. Here, we applied microbubble ozonation to treat pharmaceuticals and personal care products (PPCPs) in several municipal secondary effluents. Compared with conventional ozonation, microbubble ozonation efficiently eliminated both ozone-reactive and ozone-resistant PPCPs and greatly reduced the ozone doses in the complex water matrixes of the secondary effluents. In addition, compared with millibubble ozonation, the removal of chemical oxygen demand (COD) increased by 32.0%–67.2% at 60mg/L ozone dose during microbubble ozonation. The carbon emission of microbubble ozonation varied in different water matrix, and was 47–76% less than that of millibubble ozonation. The oxidizing capacity ratio of microbubble to millibubble for PPCPs was between 1.26 to 3.50 times, and ozone-resistant PPCPs removal was enhanced more than ozone-reactive PPCPs by microbubble ozonation. Specifically, the oxidizing capacity ratio of microbubble to millibubble for carbamazepine (ozone-reactive) was 1.30 to 2.43 times, whereas that for N,N-diethyl-3-tolumide (ozone-resistant) was 1.88 to 3.50 times. Microbubble ozonation also greatly decreased the UV absorbance and fluorescence for all of the water samples. The UV absorbance at 254, 280, and 320nm decreased by 64.0%–83.8%, and the fluorescence peak intensity decreased by more than 94%. Surrogates for the removal of PPCPs and COD were evaluated and compared. This study provides new insights into the application of microbubble ozonation to control PPCPs in secondary effluents.

Synthesis of Highly Stable Coumarin-Based Fluorescent Dye, Its Photophysical Properties and Stability in PLA Film and Application Towards Sensing Toxic Ions.

New materials were designed and synthesized by introducing electron donor and acceptor groups using coumarin as the basic unit. In addition, two more materials with similar structures were synthesized for the comparison of their optical properties and stability. The solvent effect and the photo physical aggregation properties of aggregation caused quenching (ACQ) in the ratio of water and DMF were also investigated. In addition, we checked the detection ability for anions, and the optical properties of the materials at different pH were also investigated. The photo stability of these synthesized materials was studied, and interesting results were obtained. Based on these synthesized materials, we produced films by introducing color materials into PLA films. PLA film is characterized by the absence of plastic waste due to carbon reduction and biodegradation effects from using biomass instead of fossil fuels as raw materials, but it has the disadvantage of low light stability. By introducing high-photo stability pigment materials, the photo stability of the film can be corrected, and UV protection can be provided. The UV absorbance and fluorescence intensity of the film with the dye materials were checked, and the mechanical properties and thermal stability of the film changed when the coloring material was introduced compared to the conventional PLA film.

The role of extraction method to collagen substrates in enzymolysis of type I collagenase

Collagens are ubiquitous biomaterials in animal tissues whose characteristic triple-helical structure can only be hydrolyzed under physiological conditions by a few specific proteases. At present, information on the differences of collagenase hydrolysis behavior to collagen substrate caused by extraction methods is still lacking. Acid-relaxed extracted collagen (ARC) and acetic acid-pepsin extracted collagen (APC) were obtained from bovine hide by acetic acid and acetic acid-pepsin extraction method, respectively. The enzymolysis behavior of type I collagenase on ARC and APC were investigated by means of fluorescence spectra, UV spectra, and determination the release of hydrolysates into the supernatant. The results revealed that APC showed a lower molecular weight, a higher pI (5.59) and denaturation temperature (Td = 66.9 °C) than that of ARC (pI = 4.67, Td = 57.8 °C). Moreover, APC demonstrated greater resistance to type I collagenase than ARC. The cleavage on the non-helical terminal domains by pepsin might play the role in the better thermal stability, the higher pI, and the more collagenase resistance of APC than ARC. The findings of this work should provide new insights into collagenase hydrolysis behavior and facilitate targeted utilization of collagen extracted by various method.

Quantitative and Rapid In Vivo Imaging of Human Lenticular Fluorescence.

To quantitatively investigate the chemical origins of near-UV excited fluorescence in the crystalline lens, and demonstrate the potential usefulness of a rapid and noninvasive diagnostic approach for screening and monitoring of lens damage. Anterior segment UV fluorescence imaging was applied to a population of 30 healthy adults, ages 18 to 64 years. Absolute fluorescence intensities and intensity ratios were compared across the population as a function of age. Fluorescence quantum yield (FQY) was calculated from imaging results based on a previous radiometric characterization. Typical FQYs at 365nm excitation are approximately 0.2% for healthy adults. Intensity and FQY were observed to increase significantly with age, consistent with ex vivo and confocal microscopy studies. The ratio of blue to green fluorescence is strongly correlated with FQY and age, suggesting that both increases in fluorophore concentration and changes in composition occur with age. Fluorescence data is quantitatively and qualitatively consistent with pyridine nucleotides in young adults, and changes with age are consistent with formation of β-carbolines or advanced glycation end products. Intralens variation is consistent with increased oxidation or glycation in the lens nucleus relative to the cortex. Lenticular fluorescence can be measured rapidly, accurately, and quantitatively in vivo which provides a spatially resolved, quantitative measure of lens chemistry, including damage from oxidation and glycation. Careful interpretation of fluorescence intensities and intensity ratios can provide chemical insight into lens health. Anterior segment UV fluorescence imaging can thus serve as a useful tool for screening, monitoring, and research of lens damage and cataract formation.

Unveiling the Potential of Ultraviolet Fluorescence Imaging as a Versatile Inspection Tool: Insights from Extensive Photovoltaic Module Inspections in Multi‐MWp Photovoltaic Power Stations

UV fluorescence imaging (UVF) has the potential to grow into a powerful, informative, and economically attractive inspection method for photovoltaic (PV) power stations. UVF demonstrates the ability to indicate differences in polymer types and degradation states in backsheets and encapsulation materials of PV modules. The data acquisition rate of UVF measurements is 10 to 15 times higher than that achieved by state‐of‐the‐art near‐infrared spectroscopy, enabling the mapping of the bill of materials (BoMs) and degradation state for every module in large PV arrays. Combinations of UVF with vibrational spectroscopies allow the polymer BoMs to be recognized and correlated with aging phenomena such as metal corrosion or potential induced degradation. UVF imaging can also be used for conventional visualization of nonmaterial‐related anomalies, such as hot cells or cell cracks. The low purchase cost of the equipment makes UVF an affordable and high‐throughput diagnostic method yielding comprehensive information that would otherwise only be accessible by combining several slower and more laborious methods. Automated UVF image analysis and refinements of correlations between different BoMs and UVF pattern geometry can further unlock the potential of UVF as a straightforward tool accessible to all stakeholders and promote proactive strategies for the optimization of the reliability and performance of PV power stations.

Testing of UV fluorescence marking with daily recaptures of a low-mobile bush-cricket species

The primary goal of developing new mark–release–recapture (MRR) methods is to make MMR more cost-effective and able to provide more information. To test the effectiveness of UV fluorescence marking, a case study was carried out on an Isophya costata population occurring in a mown grassland with a heterogeneous vegetation pattern. The marked individuals were examined daily, from the emergence of imagos until the mowing of the habitat. The 40 marked insects (20 males and 20 females) were recaptured in 206 cases over 16 days (32.2% of the potential maximal recaptures). The finding of males was 26.2% successful, and the finding of females was 38.1% successful. Females released in shorter and sparse vegetation were recaptured more than those released in dense vegetation or than males. Recaptures showed a significant decrease during the study period in almost all groups based on Mann–Kendall trend tests. Detections were made on the upper third of the vertical structure of the vegetation in 88% of cases. In most of the detections (males: 70%, females: 62%), the axis of the insect’s body was more likely to be located vertically. The results showed that the chance of detection is significantly reduced when the position of the insect’s body is facing the axis of UV illumination. Thus, the visibility of individuals can be greatly increased by marking all sides of the body.

The substantial generation of photochemically produced reactive intermediates (PPRIs) in algae-type zones from one large shallow lake promoted the removal of organic pollutants

Photochemically produced reactive intermediates (PPRIs) are ubiquitously present in aquatic systems and hold significant importance in biogeochemical cycles. The photochemical reaction of dissolved organic matter (DOM), known as photosensitizers upon irradiation, is the main pathway for PPRIs generation. However, the PPRIs produced by algal-derived organic matter (ADOM) and their environmental effects remains elusive. This study confirmed that substantial PPRIs were generated by ADOM in the algal-derived areas. UV absorption spectra, fluorescence spectra and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) were then indicated a significant correlation between the molecular weight of DOM and the quantum yield of PPRIs, with lower molecular weight of DOM exhibiting a higher potential for PPRIs generation. Orthogonal partial least squares (OPLS) were used to build novel multivariate predictive models for indicating the PPRIs production in algae-type zone. Also, the higher concentrations of PPRIs could significantly removal different kinds of organic pollutants, such as bisphenol A (BPA), sulfadiazine (SDZ) and 17α-ethinylestradiol (EE2). Quenching experiments further elucidated that 3DOM⁎ was the key specie for pollutants degradation, serving as the precursor to generate a series of PPRIs. This study highlighted the importance of PPRIs generated from ADOM in the natural attenuation of pollutants and provided a new insight for understanding the self-purification in aquatic system.

A method to spatially assess multipass spray deposition patterns via UV fluorescence and weed population shifts

AbstractSpray deposition patterns from agricultural sprayers are traditionally sampled discretely along a field transect accounting for 0.5% or less of the treated area. Such methods may not fully capture the dimensional variability inherent in large‐scale, multiple‐pass spray applications, especially evident from an agricultural spray drone (ASD). This study investigated the utilization of UV‐fluorescent dye and nighttime aerial imaging techniques to assess large‐scale, multipass spray deposition patterns. Accuracy of digital hue from UV‐fluorescent photography to predict deposition of proxy dye was confirmed via fluorometry assessed intensity levels of extracted UV‐fluorescent dye from 384 Petri dishes placed prior to treatment. Results showed that ASD applications, regardless of nozzle type, exhibited greater spatial variability within the target area compared to ride‐on sprayer applications, primarily due to overapplication. Additionally, the ASD generated spray drift to adjacent nontarget areas that was at least three times more than that of ride‐on and spray‐gun sprayers. Multipass deposition was further assessed via in situ smooth crabgrass infestation following treatment with quinclorac or topramezone by multipass ASD or hand‐held, four‐nozzle spray boom. Weed infestation annotated from overlaid grids with 9.3‐dm2 ground resolution inconsistently detected spatial heterogeneity between transects assessed along the center and edge of each sprayer pass. The ASD controlled smooth crabgrass 11% more than the hand‐held sprayer, albeit with an 18% increase in spray drift to nontarget areas, similar to the UV‐fluorescence study. Digitally assessed average hue of fluorescence photography appears to be a viable method to assess multidimensional and continuous spatial relationships of spray deposition.

A Carbazole-based Fluorescent Probe with AIE Performance and a Large Stokes Shift for Peroxynitrite Detection and Imaging in Live Cells.

A carbazole-based fluorescent probe YCN with AIE performance and a large Stokes shift (242nm) shift was synthesized by attaching 4-acetonitrile pyridine to the 3-phenylaldehyde butylcarbazole. Its structure was characterized by 1H NMR, 13C NMR and MS. Probe YCN has high selectivity and sensitivity toward ONOO-. The addition of ONOO- to the probe YCN solution results in a noticeable color change from pale yellow to colorless under natural light, and a fluorescent color change from bright orange-yellow to bright yellow-green under a 365nm UV lamp, which can be distinguished by the naked eye. The research results on the reaction mechanism showed that when YCN reacted with ONOO-, -C = C- was oxidized and broken into -CHO, and the ICT effect was significantly inhibited, resulting in changes in UV absorption and fluorescence emission phenomenon. The recognition mechanism was verified by 1H NMR, mass spectrometry (MS) and density function theory (DFT) calculations. The experiments of live cells imaging suggested that compound YCN can be used as a fluorescent probe for the detection of ONOO- in HeLa cells. This result indicates that YCN has potential application prospects in the biological aspects.

MULTI - ANALYTIC STUDY OF ORIENTAL MANUSCRIPTS IN BOSNIA AND HERZEGOVINA DATING FROM THE 15TH - 19TH CENTURY

The objective of this study was the analysis of materials used in five Oriental manuscripts from Bosnia and Herzegovina dating from the 15th - 19th century. The manuscripts were examined using various analytical techniques ranging from a series of preliminary tests (visual inspection, microchemical tests, thin layer chromatography (TLC), acidity status, UV fluorescence) to Fourier-transform infrared (FTIR) spectroscopy, X-ray fluorescence (XRF), optical and scanning electron microscopy (SEM-EDS). The obtained results showed that the manuscripts were made using paper, ink and pigments derived mainly from natural sources. The paper was made from either flax fibers or the combination of flax and hemp fibres and was often sized with egg white and alum to improve its quality. Both carbon black and iron-gall inks were used for the main text, whereas vermillion was chosen only for red ink. This research provides a valuable insight into the production techniques used in Oriental manuscripts from Bosnia and Herzegovina during that period. It also represents a template approach for manuscript characterisation and science-based paper conservation.

Inclusion complexes of novel formyl chromone Schiff bases with β-Cyclodextrin: Synthesis, characterization, DNA binding studies and in-vitro release study

The present study involved the synthesis of five novel Schiff bases (SB1-SB5) of formyl chromone and their inclusion complexes with β-cyclodextrin through kneading approach to enhance the solubility and stability of SBs. Characterization was conducted using FTIR, NMR, SEM, TEM, p-XRD, and Mass Spectrometry. UV fluorescence and pH stability studies confirmed the formation of the inclusion complex. Structural validation of complexes was conducted via molecular docking (PDB ID: 1BFN) and 50 ns MD simulation study. DFT studies were performed on SBs using B3LYP/6–31 + G(d,p) basis set. All SBs exhibited favorable ADME properties and high binding interactions were observed in molecular docking with ctDNA (PDB Id: 1BNA). Further, in-vitro UV absorption and fluorescence experiments demonstrated strong ctDNA interactions for all Schiff bases, with binding constants in the order of 105 M−1, indicating groove binding mode. Among the SBs, SB4 exhibited the highest affinity for DNA grooves, with a binding constant (Kb) of 1.7 × 106 M−1. However, the SB4/β-Cyd inclusion complex also interacted with DNA but with low binding constants compared to SB4. An in-vitro release study of SB4/β-Cyd, revealed 78.92 % dissolution of the inclusion complex, highlighting its potential for enhanced solubility and stability in biological systems.

Fluorescence switch based on Prussian blue nanoparticles and CdSe quantum dots for dual-channel detection of hydrazine hydrate and hydrogen peroxide

The detection of hydrazine hydrate and hydrogen peroxide is becoming increasingly important since they are of significance in industrial production and diverse applications in several fields. In this work, a Prussian blue (PB) and CdSe quantum dots based fluorescent switch PB@SiO2/CdSe@SiO2 is constructed, which is developed as a platform towards the detection of hydrazine and hydrogen peroxide. The nanocomposite can realize the switching between fluorescence quenched and restored states by transforming PB between oxidized and reduced states by redox reactions. Fluorescence spectroscopy and UV–vis absorption spectroscopy are employed to detect N2H4 and H2O2 with low detection limits, wide detection ranges and short response time. The proposed preparation method may also be useful for the assembly of other quantum dot nanocomposites, and these properties make PB@SiO2/CdSe@SiO2 potentially applicable in the field of environmental detection.

The impacts of different modification techniques on the gel properties and structural characteristics of fish gelatin

Fish gelatin hydrogels are typically characterized by weak texture and poor thermal stability. To address this issue, fish gelatin (FG) was modified using κ-carrageenan (κC) and transglutaminase (TG). FG-κC, FG-TG, and FG-κC-TG gels were prepared. The results demonstrated that the particle size and textural properties of FG gels were significantly enhanced by κC and κC-TG composite modifications, and their zeta potential was reduced (P < 0.05). As opposed to that, the improvement effects of TG modification were weaker. The highest particle size and hardness, along with the lowest zeta potential, were exhibited by the FG-κC-TG0.06% gel. Additionally, the FG-κC-TG gel system possessed higher apparent viscosity and elastic storage modulus. Fluorescence spectroscopy and UV absorption analysis indicated that fluorescence intensity was reduced by all three modification methods, and the conformational structure of FG was altered to varying degrees. Microstructure, FTIR, and XRD results revealed that the number of hydrogen bonds and isopeptide bonds in the composite gel systems was increased by κC and κC-TG modifications, enhancing the stability and orderliness of the gel's helical structure, and forming larger aggregates and denser network structures. Furthermore, due to the presence of covalent cross-linking, improved thermal stability was exhibited by the modified gelatin hydrogels. This study not only provides theoretical support for enhancing the performance of fish gelatin but also facilitates the application of modified fish gelatin in improving the sensory quality and flavor characteristics of food, as well as in serving as a matrix material in the biomedical field.

Hydroxyl Radical-Induced Oxidation on the Properties of Cathepsin H and Its Influence in Myofibrillar Proteins Degradation of Coregonus peled In Vitro.

The most frequently occurring protein modification in fish postmortem is oxidization, which further affects meat quality through multiple biochemical pathways. To investigate how hydroxyl radicals affect the structure of cathepsin H and its ability to break down myofibrillar proteins in Coregonus peled, cathepsin H was oxidized with 0, 0.1, 0.5, 1, 5, and 10 mM H2O2 and subsequently incubated with isolated myofibrillar proteins. The results showed that as the H2O2 concentration increased, the carbonyl and sulfhydryl contents of cathepsin H significantly increased and decreased, respectively. There were noticeable changes in the α-helix structures and a gradual reduction in UV absorbance and fluorescence intensity, indicating that oxidation can induce the cross-linking and aggregation of cathepsin H. These structural changes further reduced the activity of cathepsin H, reaching its lowest at 10 mM H2O2, which was 53.63% of the activity at 0 mM H2O2. Moreover, desmin and troponin-T all degraded at faster rates when cathepsin H and myofibrillar proteins were oxidized concurrently as opposed to when cathepsin H was oxidized alone. These findings provide vital insights into the interaction mechanism between oxidation, cathepsin H, as well as myofibrillar protein degradation, laying a groundwork for understanding the molecular mechanisms underlying changes in fish meat quality after slaughter and during processing.

Preliminary observations of skeletal UV fluorescence in fresh and preserved snakes

Preliminary observations of skeletal UV fluorescence in fresh and preserved snakes

Enhanced detection of UV fluorescence from food products and tissue using lanthanide-doped polymer composite membranes

We demonstrate polymer composite membranes that can be coupled to conventional spectroscopic tools for enhancing the detection of weak UV fluorescence signals. The membranes incorporate a down-conversion phosphor with lanthanide ions allowing for the detection of UV emission from biomolecules commonly found in food products. We also explore their capability to discern between healthy and wounded tissue through measurements of the UV autofluorescence emission from skin. Our results show that the composite membranes have great potential to improve UV fluorescence detection in applications related to the biomedical, pharmaceutical and food areas.

Developing a novel ultraselective and ultrasensitive label-free direct spectrofluorimetric nanobiosensor for direct highly fast field detection of explosive triacetone triperoxide

BackgroundDirect detection of the notorious explosive triacetone triperoxide (TATP) is very difficult because it lacks facile ionization and UV absorbance or fluorescence. Besides, the current indirect methods are time-consuming and need a pre-step for TATP cleavage to hydrogen peroxide. Moreover, they commonly show significant false-positive results in the presence of some camouflage which limits their field applications. Herein, for the first time, a novel label-free field-applicable spectrofluorimetric nanobiosensor was developed for direct TATP detection using a novel activated-protein protected gold nanocluster (ABSA-AuNCs; QY = 28.3 %) synthesized by a combined protein-assisted-ultrasonication procedure. ResultsThe ABSA-AuNCs revealed a fluorescence spectrum centered at 330.0 nm which was significantly quenched by TATP (binding constant = 154.06 M-1; ΔG = −12.5 kJ mol−1; E(%) = 88.5 %). This phenomenon was used as a basis for direct TATP quantification, providing a working range of 0.01–40.0 mg L−1 and a detection limit of 6.7 μg L−1 which is the lowest LOD provided for TATP detection up to now. A %RSD of 0.9 % and 1.56 % was obtained for repeatability and inter-day reproducibility, respectively. The selectivity was checked against a variety of camouflages, revealing ultra-selectivity. Several synthetic samples prepared by several camouflages and real samples (clay soil and real water media) were analyzed, revealing quantitative recoveries of TATP. SignificanceDuring the production of the notorious explosive TATP, it can be discharged into water and soil. This novel method eliminated the false-positive results of traditional methods and is applicable for direct quantitative detection of camouflaged TATP and its residues in real soil and water samples in a highly short response time (2 min). The camouflaged TATP analysis is important for tracking the terrorist attacks in field conditions and analysis of soil and water can provide a first indication of the location of the production site.

Connecting Stories: Investigations of a Seventeenth-century Mercator Hand-painted Map

ABSTRACT A seventeenth-century hand-painted map entitled Walachia, Servia, Bulgaria, Romania, printed with the original copper plate engraved by Gerardus Mercator, was investigated using portable, non-invasive spectroscopic and imaging methods. X-ray fluorescence spectrometry, UV fluorescence imaging, and short-wave infrared hyperspectral imaging were correlated to characterize pigments, differences in materials, previous interventions, and specific types of degradation. The results showed evidence for the use of vermilion, red lead, a green copper-based pigment, a gray-blue cobalt-based pigment, a chromate-based yellow pigment, and gold leaf, and even inferred the possible use of black ferro-gallic ink, thus highlighting both original materials and the likely presence of at least one previous restoration from the nineteenth century. Hyperspectral imaging was able to discriminate the most significant coloring materials, while UV fluorescence imaging suggested the use of organic material, both as a coating for the gold leaf and as a component in the mixture to temper the vermilion and the green copper-based pigments.