Seite - 224 - in The Vienna Genesis - Material analysis and conservation of a Late Antique illuminated manuscript on purple parchment

224 The miniatures of the Vienna Genesis: colour identification and painters’ palettes ite (Table 2). As blue pigment, azurite was mixed with lead white. Shading was applied with indigo. Highlights on top of blue layers were added in lead white. Contours and folds were painted in carbon black. The use of the copper containing pigment azurite, 2Cu2CO3·Cu(OH)2, has resulted in migration of copper ions to the other side of the fo- lio, in brown discoloration and in degradation of the parchment, a phenomenon similar to the effect of free copper ions on paper14. The migration is visible as dark shadows. The degradation has caused losses in the miniatures. In the XRF spectrum high copper (Cu) and lead (Pb) signal intensities confirm the use of azurite mixed with lead white (Fig. 25). In the FORS spectra, azurite is identified by the absorption maximum at 640 nm (Fig. 2). Raman spectroscopy of a loose blue particle from folio 13 also confirms azurite. On folio 11, the copper ions from the blue wings of the angels on page 21 have caused dark shadows on page 22 (Fig. 26). The cloth of the servant was painted in azurite. The blue pigment is typically coarser than ultramarine. The size of azurite particles is in the range 20–40 µm. The use of indigo for shades, lead white for highlights and carbon black for folds is visible. Under the microscope at 32x magnification, the azurite particles can be seen (Fig. 27). Azurite shows lighter blue tones than ultramarine, some azurite particles even reveal green- ish tones15. 14 Hofmann et al., 2015. 15 Eastaugh et al., 2004, Optical Microscopy of Historical Pigments, pp. 50–51. Fig. 25: XRF spectrum of blue pigment (MP11_1) on folio 11, page 23. A spectrum of the parchment of folio 6 (MP6_5) shows the background signal detected. Open-Access-Publikation im Sinne der CC-Lizenz BY 4.0