Page - 104 - in The Vienna Genesis - Material analysis and conservation of a Late Antique illuminated manuscript on purple parchment

104 Identification of the purple dye on the Vienna Genesis from scientific methods suggested a completely different story: it revealed that shellfish purple has to date never been directly identified in any purple manuscript, and that other dyes such as folium or orchil were used instead5. It is important to keep in mind that it is not possible to detect the indigoid chromophores of shellfish purple admixed with one of these dyes due to the very low quantum yield of fluorescence emission of shellfish purple on one hand, and very low signals in Raman on the other. The analytical study on the purple dye contained on the parchment of the Vienna Gen- esis was performed in two phases: 1. non-invasive measurements were carried out in situ with portable instruments at the Austrian National Library. Further measurements were taken in the laboratory on micro-samples (ø 2 mm) of the parchment. The main aim of the non-invasive investigation was to make a preliminary identification of the dye used for 5 See among others Rosi et al., 2013; Aceto et al., 2014; Aceto et al., 2017. Table 1a: Possible sources for purple dyeing in antiquity and molecular structures for the main chromophores: Rocella tinctoria and Lasallia pustu- lata. In the lichens two type of chromophores may be found, derivatives of amino- or hidroxy-orcein. Dyed parchment samples were ir- radiated with a Xenon lamp (lirr ≥ 320 nm), photographs and L*a*b* colour coordin- ates for unaged and 310 h irradiation are given. Open-Access-Publikation im Sinne der CC-Lizenz BY 4.0