Page - 116 - in The Vienna Genesis - Material analysis and conservation of a Late Antique illuminated manuscript on purple parchment

116 Identification of the purple dye on the Vienna Genesis in ammonia for at least three weeks. The procedure, though managed with expertise by the artisans, was not an industrial process and was therefore subject to some variations from one batch to another, or from one craftsman to another. Finally, the possible use of different lichen species must be considered depending on the availability of raw materials. Summary and conclusion Raman microscopy disclosed the molecular fingerprint for the fundamental orcein struc- tures shared by all the amino and hydroxy derivatives, and present in parchment samples dyed with lichens such as Roccella tinctoria and Lasallia pustulata, table 1a and figure 9. These conclusions were obtained comparing the reddish-purple parchment with unaged reference samples. On the other hand, aged references of dyed parchment presented us with further insights into the lichen species used. Micro-spectrofluorimetry showed that the closest match to the historical parchment was obtained with an aged reference sample dyed with Lasallia pustulata (Fig. 7 and 8). Therefore, the lichen used to dye the Vienna Genesis folios would have dyeing properties more like Lasallia pustulata. This technique also indicated the presence of another type of chromophore that for the moment could not be characterised by a chemical structure. Overall, the spectroscopic techniques applied in situ indicated the presence of an orchil-dyed parchment, and Raman microscopy (through SERS) provided the dye fingerprint. At this stage, therefore, the identification of orchil on the parchment of the Vienna Genesis is indisputable. Literature Aceto, M. 2018. Unpublished data. Aceto, M., A. Idone, A. Agostino, G. Fenoglio, M. Gulmini, P. Baraldi, and F. Crivello. 2014. Non-invasive investigation on a VI century purple codex from Brescia, Italy. Spec- trochimica Acta A 117: 34–41. Aceto, M., A. Arrais, F. Marsano, A. Agostino, G. Fenoglio, A. Idone, and M. Gulmini. 2015. A diagnostic study on folium and orchil dyes with non-invasive and micro-de- structive methods. Spectrochimica Acta A 142: 159–168. Aceto, M., A. Agostino, G. Fenoglio, A. Idone, F. Crivello, M. Griesser, F. Kirchweger, K. Uhlir, and P. Roger Puyo. 2017. Analytical investigations on the Coronation Gospels manuscript. Spectrochimica Acta A 171: 213–221. Barreira, C., M.J. Melo, R. Araújo, R., and C. Casanova. 2016. Through the eyes of Sci- Open-Access-Publikation im Sinne der CC-Lizenz BY 4.0