Seite - 111 - 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 111 ation spectra were obtained. The latter may simulate the absorption spectrum. One of the species is characterised by an excitation spectrum with a maximum at 535 nm whereas the second species displays a maximum at 590 nm (Fig. 5). On the other hand, the emission maxima are similar, 595 and 600 nm, respectively (Fig. 6). When compared to artificially aged samples of Lasallia pustulata, we find a very good match with the chromophore char- acterised by excitation (Fig. 7) and emission maxima (Fig. 8) at 590 and 600 nm (chromo- phore #2), respectively. The same was observed for parchment dyed with Rocella tinctoria (results not shown). Compared to unaged orcein-treated samples, a 5 nm shift to longer wavelengths was observed in the emission spectrum (Fig. 8). In summary, a very good match was obtained with representative spectra found in the original purple parchment (chromophore #2) and an aged reference sample dyed with Lasallia pustulata. The results of SERS analysis on the samples from the Vienna Genesis and Cod. Ser. n. 2804 are shown in figure 9. Raman microscopy could disclose the molecular fingerprint for the fundamental orcein structures, shared by all the amino and hydroxy derivatives, Table 1. The main assignments are described next14; bands 517 cm-1 ascribed to δ(COC), 619 cm-1 attributed to δ(COO), 798 with a shoulder at approx. 820 cm-1 due to ν(CC), ν(CN), 14 Rosi, 2013; Doherty et al., 2014; Melo, 2016. Fig. 4: Spectrofluorimetry spectra of folium, orchil, the parchment of the Vienna Genesis (folio 1, page 1) and of Cod. Ser. n. 2804. The spectrum of undyed parchment is included. Open-Access-Publikation im Sinne der CC-Lizenz BY 4.0