Page - 206 - in The Vienna Genesis - Material analysis and conservation of a Late Antique illuminated manuscript on purple parchment

206 The miniatures of the Vienna Genesis: colour identification and painters’ palettes tral range of the detector was 200–1160 nm. According to the features of the monochro- mator (slit width 50 µm, grating of UA type with 300 lines/mm) and of the detector (2048 pixels), the best spectral resolution was 2.4 nm calculated as FWHM (Full Width at Half Maximum). Diffuse reflectance spectra of the samples were referenced against the WS-2 reference tile provided by Avantes and guaranteed to be reflective at least at 98 % within the investigated spectral range. Blank correction was not efficient on both the extremes of the spectral range, therefore the regions 200–350 nm and 1100–1160 nm were not considered in the discussion. The diameter of the investigated area on the sample was 1 mm. In all of the measurements, the distance between the probe and the sample was kept constant at 2 mm, corresponding to the focal length of the probe. To visualise the samples, the probe was equipped with a USB endoscope. The instrumental parameters were as follows: 10 ms integration time, 100 scans for a total acquisition time of 1 s for each spectrum. The system was managed by means of AvaSoft v.8 dedicated software, running under Windows 7. An Ocean Optics (Dunedin, Florida, USA) Jaz model spectrophotometer was em- ployed to record molecular fluorescence spectra. The instrument is equipped with a 365 nm Jaz-LED internal light source. An FCR-7UV200-2-1.5x100 probe (same as FORS) is used to drive excitation light on the sample and to recover the emitted light. The spec- trophotometer works in the range 191–886 nm. According to the features of the mono- chromator (200 µm slit width) and detector (2048 elements), the spectral resolution avail- able is 7.6 nm calculated as FWHM. The investigated area on the sample is 1 mm in diameter. In all of the measurements, the sample-to-probe distance was kept constant to 12 mm, corresponding to the focal length of the probe. To visualise the samples, the probe was equipped with a USB endoscope. The instrumental parameters were as follows: 4 s integration time, 3 scans for a total acquisition time of 12 s for every spectrum. The system is managed by SpectraSuite software running under Windows 7. Micro images were taken with a Lumenera (Ottawa, Canada) Infinity Lite model cam- era with 1.5 MPixel and CMOS sensor. The camera was connected with a Navitar (Roches- ter, NY, USA) Zoom 6000 optical lens allowing a 10x–80x magnification range10. Illumin- ation of the sample was obtained by means of an Opto Engineering (Mantova, Italy) LT RN 23/W model LED ring light, providing cool white light, so having a minimum impact on the sample. Raman analysis was performed with a high-resolution dispersive Horiba (Villeneuve d’Ascq, France) LabRAM HR model spectrophotometer coupled with a confocal micro- scope. The instrument is equipped with a 633 nm excitation laser, two (600 and 1800 lines/ mm) dispersive gratings, an 800 mm path monochromator and a Peltier cooled CCD 10 The microimages were taken by Valerio Capra, Laboratorio di restauro del libro, Abbazia benedit- tina dei S. S. Pietro e Andrea, Borgata San Pietro 10050, Novalesa (TO), Italy. Open-Access-Publikation im Sinne der CC-Lizenz BY 4.0