Seite - 106 - in The Vienna Genesis - Material analysis and conservation of a Late Antique illuminated manuscript on purple parchment

106 Identification of the purple dye on the Vienna Genesis on the nature of the chromophores present. Surface enhanced Raman spectroscopy (SERS) made it possible to obtain a definitive fingerprint identification of the dye by analysis of the micro-sample. Finally, X-Ray fluorescence spectrometry (XRF) was used to detect bromine. For comparison, the same measurements were carried out on a micro-sample of parch- ment taken from Codex Serius nova 2804 (Cod. Ser. n. 2804) from the Austrian National Library. Cod. Ser. n. 2804 is a fragment of purple parchment without text that is dated to the 6th century. Methods of analysis UV-visible diffuse reflectance spectrophotometry with optic fibres (FORS) analysis was per- formed with an Avantes (Apeldoorn, The Netherlands) AvaSpec-ULS2048XL-USB2 model spectrophotometer and an AvaLight-HAL-S-IND tungsten halogen light source. Detector and light source were connected with fibre optic cables to an FCR-7UV200-2-1,5x100 probe. In this configuration, light is sent and retrieved with a single fibre bundle positioned at 45° with respect to the normal surface, in order to exclude specular reflectance. The spec- 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 area investigated 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 1.0 s for each spectrum. The sys- tem was managed by means of AvaSoft v. 8 dedicated software, running under Windows 7. For Spectrofluorimetry, an Ocean Optics (Dunedin, Florida, USA) Jaz model spectro- photometer was used 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 spectrophotometer works in the range 191–886 nm. According to the features of the monochromator (200 µm slit width) and detector (2048 elements), the spectral resolution available is 7.6 nm calculated as FWHM. The investigated area on the sample is 1 mm in Open-Access-Publikation im Sinne der CC-Lizenz BY 4.0