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The effect of paper thermal destruction on its luminescence spectra and luminescence excitation spectra in the spectral ranges of 400-550 nm and 250-450 nm, respectively, was studied. It is proposed to use the characteristic changes in the intensity and shape of the luminescence spectra as a criterion for the state of paper insulation of power transformers. On the basis of the analysis performed, it was concluded that when luminescence is excited at a wavelength of 360 nm, none of the main components of the paper can contribute to the recorded luminescence spectra. It is assumed that the resulting luminescence spectra are due to the emission of various impurities that enter the paper during its production.

Graphical abstract Highlights • Hyper spectral imaging was used to get many spectra in a short time. • The identification of eight paper types was done by using machine learning. • Even papers with very similar spectra could be distinguished with high accuracy. • For 68,400 spectra per sample, the accuracy was 87.8%. Abstract Paper is non-uniform; thus, it is difficult to ascertain whether the slight differences in near-infrared absorption spectra are caused by the difference in paper type or the paper's non-uniformity. We used near-infrared hyperspectral imaging to measure the spectra of many different points quickly for eight different paper samples. Next, we analysed the data using machine learning and constructed a model to ascertain whether the differences in the spectra are due to the difference in paper type or the paper's non-uniformity. Even papers with very similar spectral shapes were distinguished with high accuracy with this method. As the number of spectra used to construct the classification model increased, the accuracy of the classification model increased. With 6840 spectra per sample, the accuracy exceeded 85%, and with 68,400 spectra per sample, the accuracy for identification was 87.8%. [ABSTRACT FROM AUTHOR]

Abstract: The application of diffuse reflectance UV–VIS–NIR spectroscopy is proposed to differentiate 20 office paper samples, which had been deemed similar by a preliminary visual examination under several different lighting sources. The samples were firstly screened on the basis of the qualitative appearance of their spectra. A further discrimination was obtained by taking into account three parameters: the average reflectivity of the paper samples in the range 680–900nm, and the integrated intensity of the absorption peak in the UV range at 272nm and at 360nm. The homogeneity of these parameters on both sides of the paper sheets was assessed, detecting a very uniform distribution of the optical brighteners. A special focus was posed on the determination of the discriminative power, in order to give a quantitative parameter on the proposed procedure, which is important when reporting results to the Court. The remarkable achievement of differentiating all the examined samples was obtained by UV–VIS spectroscopy, a very less expensive technique which is readily available in practically all forensic laboratories. [Copyright &y& Elsevier]

The colorfastness of several traditional Japanese colorants upon exposure to atmospheric ozone was tested in a chamber exposure experiment. Samples, in the form of colorants applied to paper, dyes on silk cloth, and colorants on a nineteenth- century Japanese woodblock print, were exposed to an atmosphere containing 0·40 parts per million ozone at 22°C and 50% RH, in the absence of light, for 12 weeks. Color differences, calculated from the measured diffuse reflectance spectra, were used to assess the rate and extent of the ozone fading. Of the colorants applied to paper, orpiment was the only inorganic pigment that showed severe color loss after ozone exposure. Several organic colorants on paper also reacted, including the widely used plant colorants ai (indigo) and ukon (turmeric). The woodblock print, produced using the plant-derived colorants beni (safflower), ai (indigo), shiō (gamboge) and aigami (dayflower), showed significant ozone fading only in the blue and green areas, which contain ai. Several of the dyed silk cloths also exhibited some color change in this experiment, suggesting that prolonged exposure to atmospheric ozone could pose a risk to these materials as well. [ABSTRACT FROM AUTHOR]