Seite - 207 - in The Vienna Genesis - Material analysis and conservation of a Late Antique illuminated manuscript on purple parchment

Hofmann, Rabitsch, Malissa, Aceto, Uhlir, Griesser, Calà, Agostino, Fenoglio 207 detector. The optical arrangement gave a spectral resolution of about 2 cm−1. Spectra were taken placing samples on the microscope stage and observing them with long working distance, 20x, 50x and 80x objectives. The sampled area was identified and focused using either a video camera or the microscope binoculars. Laser power at the sample was initially kept low (< 100 µW) by means of a series of neutral density filters in order to prevent any thermal degradation of the molecules, then gradually increased to the optimal signal-to- noise ratio setting. Exposure time was 1–120 s according to individual needs. The system was managed with LabSpec 5 software running under Windows XP11. For Surface Enhanced Raman Spectroscopy (SERS) mode analysis, a colloidal paste of silver nanoparticles was prepared following a procedure based on the Lee and Meisel reduction of silver nitrate. The colloidal paste (1 µl) is poured on the sample and allowed to dry. After 10 minutes, the SERS analysis is performed and the spectral response obtained. The sample size was less than 1 mm. Scanning electron microscope (SEM) images at different magnification were recorded on a Quanta 200 FEI (Hillsboro, Oregon) scanning electron microscope equipped with EDAX (Mahwah, New Jersey) EDS attachment, using a tungsten filament as electron source at 20 keV. The instrument was used in E-SEM mode (90 mbar of water pressure in chamber) in order to avoid samples metallisation. Each miniature was examined under normal and raking light. Ingrid Oentrich12 took photographs of each page under Ultraviolet light (UV). Michael Eder13 made Infrared reflectography images (IRR) of each miniature. He used a Hamamatsu InGaAs camera C 12741-03 with an IR sensitivity of 950 to 1700 nm. The single shots were put together with Microsoft ICE and Photoshop. With a Wild stereo microscope M 400 (Type 126269), the analysed measurement points of the colours were investigated under the microscope at 6.3x–32x magnification. The points were compared with other areas of similar colour. Digital images were taken with a Nikon D7000 camera equipped with a Nikon cam- era adapter for microscopes (SKU: CA-NIK-SLR). Analytical results were correlated with visual examination and art technological observations. A spreadsheet per miniature con- tains the number of the investigated points, the results of µ-XRF, of FORS, optical and technological descriptions, observations under UV light and of infrared reflectography images as well as the number of the microscopic images. The results for every painter were summarised in the spreadsheet. In the following, the palettes are described for each of the assumed seven painters (Table 2). 11 Angelo Agostino and Gaia Fenoglio collaborated in the interpretation of FORS, fluorimetry and Raman spectral responses. 12 Ingrid Oentrich, Department of Digital Services, Austrian National Library. 13 Michael Eder, Kunsthistorisches Museum Vienna. Open-Access-Publikation im Sinne der CC-Lizenz BY 4.0