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- Cultural heritage (3) (entfernen)
Nondestructive analyses of medieval reverse paintings on glass revealed the same dyes and pigments customarily used in panel paintings. However, there is one exception: the black colorant is not a carbon-based pigment, but black enamel. In this respect, the stylistic as well as the technical influence of stained glass artwork can clearly be seen on reverse paintings on glass. However, there is a crucial difference: in reverse paintings, the black enamel is not fired onto the glass but painted (cold painting). Additional analyses confirmed these findings. Based on these results, the art form "reverse painting on glass" has technically to be characterized as a mixture of "stained glass" and "panel painting" that nonetheless develops into a genre of its own.
Fe K-edge XANES measurements were performed to determine the oxidation state of iron in iron gall inks. These data are used to investigate the relationship between the Fe oxidation state and ink corrosion in historical manuscripts. The oxidation state is determined using the pre-edge based on a general variation trend that was derived from model compounds and validated here independently on a suite of samples with known oxidation state and Fe in octahedral coordination (i.e. similar to Fe in gall ink). As long as suitable references for the pure ferric and ferrous state of iron gall inks cannot be pointed out, the analysis of the pre-edge of the Fe K-edge represents the only way to acquire absolute values for the Fe oxidation state (Fe3+/Fetot) with spatial resolution for this usually non-crystalline compound. Fe3+/Fetot values for the ink samples vary between ca. 0.7 and 1.0. Spatially resolved analyses performed across ink strokes of various historical manuscripts as well as newly made samples did not reveal any systematic spatial dependence. On average, historical samples that were exposed to conservation treatments show a more oxidized state. However, the measurements demonstrate explicitly that the exposure to X-rays during the XANES acquisition affects the oxidation state of Fe in most iron gall inks.