Seite - 107 - in The Vienna Genesis - Material analysis and conservation of a Late Antique illuminated manuscript on purple parchment

Maurizio Aceto, Maria João Melo, Elisa Calà, Paula Nabais, Rita Araújo 107 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. For Micro-spectrofluorimetry, fluorescence excitation and emission spectra were re- corded with a Jobin Yvon/Horiba SPEX Fluorog 3-2.2 spectrofluorometer hyphenated to an Olympus BX51 M confocal microscope, with spatial resolution controlled with a multiple-pinhole turret, corresponding to a minimum 2 µm and maximum 60 µm spot, with 50x objective. Standard dichroic filters used at 45° were used to collect the excitation spectra (570 and 620 nm) and emission spectra (540 and 570 nm). Emission spectra were acquired exciting at 530 and 560 nm, while excitation spectra were recorded collecting the signal at 590 and 630 nm. This enables the collection of both the emission and excitation spectra with the same filter holder. Spectra were acquired on a 30 or 8 µm spot (pinhole 8 and 5, respectively) with the following slits set: emission slits = 3 / 3 / 3 mm, and excit- ation slits = 5 / 3 / 0.8 mm. The optimization of the signal was performed for all pinhole apertures through mirror alignment in the optic pathway of the microscope, following the manufacturer’s instructions. Spectra were collected after focusing on the sample (eye view) followed by signal intensity optimization (detector reading). Emission and excitation spec- tra were acquired on the same spot whenever possible. Most of the reference samples were analysed in situ. The Vienna Genesis was analysed using micro-samples. Surface enhanced Raman spectroscopy (SERS) analysis was carried out by Elisa Calà with a high-resolution dispersive Horiba (Villeneuve d’Ascq, France) LabRAM HR model spectrophotometer coupled with a confocal microscope. The instrument was equipped with a 633 nm excitation laser, a 1800 lines/mm dispersive grating, an 800 mm path mono- chromator and a Peltier cooled CCD detector. The optical arrangement gave a spectral resolution of about 2 cm-1. Spectra were taken by placing the samples on the microscope stage and by observing them with long working distance 50x and 80x objectives. The sam- pled area was identified and focused using either a video camera or the microscope binocu- lars. Laser power at the sample was kept very low (30 µW) by means of a series of neutral density filters, in order to prevent any thermal degradation of the molecules. Exposure time was 1–30 s according to needs, with 3 accumulations for each spectrum. The system was managed with LabSpec 5 software running under Windows XP. For the preparation of the sample, silver colloidal pastes were synthesised according to the procedure described by Lee and Meisel6, based on reduction of silver nitrate with citric acid. Analysis was per- 6 Lee and Meisel, 1982. Open-Access-Publikation im Sinne der CC-Lizenz BY 4.0