TED-AJ03-664 AGING INFLUENCE ON THE THERMAL AND OPTICAL PROPERTIES OF ARTISTIC GLASSES : EXPERIMENTAL DATA AND COMPARISON
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概要
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The aim of the present paper is to evaluate the influence of the aging process on the thermal and optical properties of glasses employed in the restoration of artistic windows. Therefore, 10 glass samples of different color, thickness and staining technique were examined. Half of each sample was subject to an accelerated aging process of 11 weeks in a climatic chamber (see Fig. A-1). Then, in order to evaluate the influence of the thermal stress and strain due to environmental conditions such as air temperature and relative humidity on the behavior of the glasses, the thermal expansion coefficient α of the new and aged samples was measured. Measurements were carried out in the same climatic chamber used for the aging process (see Fig. A-1), employing suitable strain gauges. Results show that the aging process could produce significant differences between the values obtained for the new and the aged samples. A general trend of increased α for the aged samples was noticed. The influence of the aging process on the radiative properties of the same samples was investigated also.[figure] Specifically, the spectral transmission and reflection coefficients were measured with a spectrophotometer Cary 2300 (see Fig. A-2); the light transmittance and reflectance and the solar direct transmittance and reflectance were calculated. Results show that the aging process influences only the reflection properties in the visible wavelength range of sample No.6,the only one stained with a particular technique called as "grisaglia" (in the box of Fig. A2); the reflection coefficient of the aged sample is greater than that of the new one; the light reflectance of the aged sample is twice that of the new one. Results suggested the extended research to 5 other samples, all stained with the grisaglia technique; four of them are antique fragments from the Arezzo and Cortona Cathedrals, one of them is a new sample employed in the restoration of the artistic windows. Results show that the antique samples have higher values of the reflection coefficients. The reason is that the aging process makes the glass surfaces decorated with the grisaglia technique smoother.[figure]
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