Abstract
The investigation and conservation of the Vienna Genesis, a Late Antique manuscript on purple parchment, included the study of parchment production and purple dyeing in the sixth century. The process of parchment making and of purple dyeing was recreated and compared with the Vienna Genesis and other manuscripts from the sixth and eighth centuries. Parchment made from the hides of young lambs and dyed with orchil resembled the folios of the Vienna Genesis. The results of material analysis and the study of parchment technology influenced decisions for the conservation and storage of the manuscript. Fragile areas of ink and parchment were stabilised with strips of adhesive coated Japanese tissue paper. The single folios are stored in folders of Japanese paper and museum matboard within a sink mat.
Zusammenfassung
Die Untersuchung und Konservierung der Wiener Genesis, einer spätantiken Purpurhandschrift, beinhaltete eine Studie zur Herstellung von Pergament und zur Purpurfärbung im sechsten Jahrhundert. Der Prozess des Pergamentmachens und des Färbens mit Purpurfarbstoffen wurde in Experimenten rekonstruiert und die Ergebnisse mit der Wiener Genesis und anderen Handschriften des sechsten und achten Jahrhunderts verglichen. Aus den Häuten junger Lämmer hergestelltes und mit Flechtenfarbstoff gefärbtes Pergament ist den Folios der Wiener Genesis ähnlich. Die Erkenntnisse aus Materialanalyse und technologischen Studien beeinflussten Entscheidungen zur Konservierung und Aufbewahrung der Handschrift. Fragile Stellen in Tinte und Pergament wurden mit Brücken von beschichtetem Japanpapier stabilisiert. Die einzelnen Folios werden in Umschlägen aus Japanpapier und Museumskarton in versenkten Passepartouts aufbewahrt.
Funding source: Austrian Science Fund
Award Identifier / Grant number: P 28898-G26
Acknowledgments
The Austrian Science Fund FWF supported the research project (P 28898-G26). We thank Inge Boesken Kanold, Zita Breu, Mark Clarke, Virginia Costa, Andrea Giovannini, Regina Hofmann-de Keijzer, Otto Kresten, Andrea Pataki, Cheryl Porter and Isabella Withworth for providing their expertise as consultants.
1 Identification of the animal species with biomolecular analysis, eZooMS
Sarah Fiddyment and Matthew Collins developed electrostatic Zooarchaeology by Mass Spectrometry (eZooMS) in collaboration with conservators at the Borthwick Archive at the University of York. eZooMS uses the principle of Peptide Mass Fingerprinting (PMF) through ZooMS analysis. However, it has been adapted to cultural heritage objects with the addition of non-invasive sampling based on triboelectric extraction developed by Fiddyment and Collins (Fiddyment et al. 2015). The method involves gently wiping the surface of the parchment with a PVC eraser and collecting the resulting eraser crumbs to be analysed. Fiddyment analysed eraser crumb samples from all 24 folios of the Vienna Genesis and from one folio of the Codex Purpureus Petropolitanus. Eraser crumb samples were extracted in a saline solution with trypsin and incubated at 37 °C for 4 h. Samples were then desalted using a C18 filter tip before being spotted onto steel plates for subsequent Matrix Assisted Laser Desorption/Ionization – Time of Flight mass spectrometry (MALDI-TOF) analysis. Resulting spectra were analysed using PMF to determine the species of origin of the parchment.
2 XRF, XRD, and SEM/EDX
Micro X-ray fluorescence spectroscopy (µ-XRF)
Silver inks, pigments, and blank parchment were analysed with energy dispersive μ-X-ray fluorescence spectroscopy (μ-XRF) with a portable instrument, provided by the International Atomic Energy Agency (IAEA), Seibersdorf Laboratories, Nuclear Science and Instrumentation Laboratory. In order to minimize absorption losses of excitation and X-ray fluorescence radiation by air and thus provide an elemental range from sodium (Na) onwards, a vacuum chamber that can be evacuated 0.1 mbar forms the centrepiece of the spectrometer. Additionally, the spectrometer is equipped with a low-power Pd tube, which was run with an acceleration voltage of 50 kV, a current of 1 mA and a measuring time of 100 s for each measurement position. The spot size is 160 μm in diameter when focused using the polycapillary of the instrument, which is placed inside the compact vacuum chamber. The chamber is sealed with a Kapton window that allows positioning of the measurement head in front of the spot analysed using two laser pointers, which cross at about 1–2 mm distance in front of the spectrometer, at the focal spot of the polycapillary. For this procedure, an internal camera is used. The fluorescence radiation emitted by the investigated sample is collected by a Si drift detector (SDD) with an active area of 10 mm2. Since an upright positioning of the folios was required by the arrangement of the spectrometer, each folio was mounted on a polyester foam with paper corners and fixed vertically on a perforated plate using a custom-made setup. The measurements were performed and evaluated by Katharina Uhlir and Antonia Malissa, the qualitative interpretation of the XRF-spectra was supported by the comparison with reference spectra of natural and synthetic pigments provided by the Conservation Science Department Kunsthistorisches Museum Vienna (KHM).
X-ray diffraction (XRD)
Micro-samples were taken from the silver ink of the Vienna Genesis to investigate the corrosion products. The analysis of the silver corrosion phases was performed by micro-X-ray diffraction (μ-XRD), i.e., with beam diameters of about 100–300 µm in contrast to the beam sizes in the mm-range for conventional X-ray diffraction techniques. For the investigation, a Malvern/PANalytical B.V. powder diffractometer EMPYREAN was used in symmetric θ -θ -geometry, where both the X-ray tube and the 2-dimensional GaliPIX photon detector are rotated symmetrically during the detection process of photons around the sample. A focusing reflection mirror, mounted in the primary beam, provided a monochromatic X-ray beam of a copper anode at the sample position with a wavelength of 0.15405 and 0.15443 nm, CuKα1 and CuKα2, respectively. The energy of the X-ray beam allowed a penetration depth in the range of a few 10 µm, dependent on the material under investigation and the incident X-ray beam angle. Hence, the phase analysis was restricted to the near surface region in contrast to the bulk analysis by e.g., neutron diffraction methods with penetration depths about one order of magnitude higher. A 300 µm slit in horizontal direction ensured a small beam on the sample position. Thus, in principle a locally restricted phase analysis on the sample is possible. The xyz-table of the instrument allowed a scan range of ±28 mm in two directions, parallel to the sample surface, and 20 mm perpendicular to the sample surface to cover the different measured positions on the samples without remounting and re-adjusting of the whole sample set-up. Klaudia Hradil and her team at the X-ray centre of the Vienna University of Technology conducted the XRD measurements.
Energy dispersive X-ray analysis in the scanning electron microscope (SEM/EDX)
Micro-samples of silver ink from the Vienna Genesis were investigated by SEM/EDX. The samples were investigated in a FEI Quanta FEG 250 SEM in high vacuum mode unless specified otherwise. X-ray micro-analyses were performed with an EDAX system equipped with an Apollo X SDD detector. The samples were investigated in their state as delivered: no sample preparation was applied. Since in all samples from the Vienna Genesis the surface of the silver ink was contaminated with material consisting mainly of organic matter mixed with mineral particles, only point analyses were performed on spots where the surface of the silver ink appeared to be clean in BSE images. The results of EDX analysis were normalized to 100% wt%. The figures of detected elements were given in percentage per weight. Rudolf Erlach conducted the investigation with SEM/EDX at the Institute of Art and Technology of the University of Applied Arts Vienna.
3 Fibre Optical Reflectance Spectroscopy (FORS)
UV-visible diffuse reflectance spectrophotometry with optic fibres (FORS) analysis was performed 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 surface normal, in order to exclude specular reflectance. The spectral range of the detector was 200–1160 nm. According to the features of the monochromator (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 and 1100–1160 were not considered in the discussion. The diameter of the investigated area on the sample was 1 mm. In all 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. Maurizio Aceto and his team investigated the pigments and dyes of the Vienna Genesis, the Codex Sinopensis and the Dagulf Psalter.
4 Microspectrofluorimetry, surface enhanced Raman spectroscopy (SERS)
For microspectrofluorimetry, fluorescence excitation and emission spectra were recorded 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 50× 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 excitation 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 spectra were acquired on the same spot whenever possible. Maria J. Melo and her team analysed most of the reference samples in situ. The Vienna Genesis was analysed using micro-samples.
SERS analysis was undertaken by Maria J. Melo and her team using a Labram 300 Jobin Yvon spectrometer, equipped with a HeNe laser operating at 632.8 nm (17 mW). Spectra were recorded as an extended scan. The laser beam was focused with 50× and 100× Olympus objective lens. The laser power at the surface of the sample varied with the aid of a set of neutral density filters (optical densities 0.6 and 1). The laser power at the surface of the samples was between 4.25 and 1.7 mW. No evidence of sample degradation was observed during spectra acquisition. More than three spectra were collected from the same sample and a silicon reference was used to calibrate the instrument. Silver colloids for SERS were prepared by chemical reduction of silver nitrate with sodium citrate, following the synthetic protocol published by Lee & Meisel (Lee and Meisel 1982). SERS analysis was performed after deposition of 0.8 μL of the silver colloid and 0.1 μL of 0.5 mol L−1 KNO3 aqueous solution onto the microsample. All spectra were collected by focusing the laser beam onto the microaggregates that formed inside the dye-colloid droplet a few seconds after the deposition of the silver nanoparticles and KNO3. Spectra were acquired continuously until the droplet dried out.
5 Oddy Test
The materials for storage were evaluated with the Oddy Test, a method developed by Andrew Oddy at the British Museum in 1970s. The Oddy Test is an accelerated corrosion test that observes the effect of pollutants emitted by the materials to be evaluated on three metal coupons (silver, copper, lead). The materials to be evaluated are exposed to 60 °C and 100% RH for 28 days. The roughened surface of the metal coupons enhances reactivity. The materials are classified in three groups:
P – materials for permanent exhibition use
T – materials for temporary use (maximum 6 months)
U – materials unsuitable for contact with valuable objects
Sabine Stanek conducted the Oddy Tests at the Conservation Science Department, Kunsthistorisches Museum Vienna (KHM).
6 Japanese Papers
Mitsumata and Mino papers were hand and custom made by Eikan Ebuchi in Kochi, a paper maker who is a member of the Association of Successors of Traditional Preservation Techniques in Japan. The fibres were cooked with soda ash (sodium carbonate, Na2CO3 decahydrate). Natural neri from tororo-aoi was used as mucilage. The papers were dried on wooden panels.
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