4 Material und Umwelt
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- 4 Material und Umwelt (2) (entfernen)
This work presents a spectroscopic study of metallic pigments and metal foils used in reverse glass paintings that were created between 1912 and 1954. Metallic pigments induce a notable sparkling effect by means of the lateral incidence of light, whereas metal foils enhance the gloss and create a glittering effect when the painting is viewed in reflected light. Both effects were desired features especially in modern reverse paintings on glass and applied by artists in manifold creative manner. The paper gives an overview on the composition of the metalfoils and metal pigments in 14 works as determined in situ by X-ray spectrometry. Metal foils made of tin, brass, aluminium and silver were found in nine paintings. Gold imitating Cu-Zn pigments in different hues and with various Cu/Zn net intensity ratios were recorded for six paintings. Silvery pigments were identified mainly as Al pigments, but also as Cu-Zn-Ni alloy in one case. Other uncommon metallic pigments were detected in Arlequin vindicatif (c. 1925) by Floris Jespers, who used not only Cu-Zn and Al pigments, but also brownish Cu and Cu-Zn-Sn pigments. Non-invasive diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) was used to classify the binding media of the metallic pigments. Drying oil and natural resin probably mixed with oil were the most common binding media. A polysaccharide-based binder was found in the silvery Cu-Zn-Ni pigment of Ohne Titel (1954) by Marianne Uhlenhuth.
This paper addresses the sensitive issue of authenticating unprovenanced manuscripts of high monetary value to certify they are genuine. Over the last decade, the popularity of material studies of manuscripts using non-destructive testing (NDT) has increased enormously. These studies are held in especially high esteem in the case of suspicious writings due to the methodological rigour they are reputed to contribute to debate. We would like to stress that materials analysis alone cannot prove that an object is genuine. Unfortunately, audiences with a humanities background often tend to disregard the technical details and treat any published interpretation of instrumental analysis as an objective finding. Four examples are outlined here to illustrate what questionable contributions the natural sciences can make in describing manuscripts that have actually been forged.