To be (purple) or not to be

The use of purple dyes or paints to impart colour to parchment of precious codices is mentioned since Late Antiquity [1]. Usually, codices dyed with Royal purple were Holy Writings texts with golden or silver inks on purple-dyed parchment. In the ancient literature, though, recipes explicitly describing the practice of colouring parchment are rare. As a consequence, our knowledge concerning the colourants effectively used is far from complete [2]. One reason is due to the fact that there is sometimes ambiguity, in bibliographic sources, among the term “purple”, which recalls the use of Tyrian purple dye, and the actual compounds used to dye in purple. Moreover, purple codices have been rarely analysed and not often the results have allowed to identify a definite colourant. At present, indeed, we have no single evidence of the use of Tyrian purple in codices, so that the presence of less valuable alternatives must be hypothesised, such as orchil from Roccella, Dendrographa, and Lecanora genera of lichens or folium from Chrozophora tinctoria; anthraquinonic dyes such as kermes or madder could be present as well, possibly applied in sequence with indigo. Anyway, we have no clear information even in cases where alternative dyes were present on parchment, since the non-invasive identification of orchil and folium is difficult. Very little spectroscopic information is available from the scientific literature (in very few instances these dyes were identified on artworks). From these considerations, it appears clear that more studies are needed to verify data from bibliographic sources. In this work some preliminary results from non-invasive analysis on purple codices are shown. The manuscripts involved are dated from the VIth to the VIIIth century: they are known as Vienna Genesis (Vienna, Österreichische Nationalbibliothek), Krönungevangeliar (Vienna, Schatzkammer), Evangeliario di Sarezzano (Tortona, Archivio Diocesano) and Codex Brixianus (Brescia, Biblioteca Queriniana). These manuscripts were analysed with X-ray Fluorescence Spectrometry (XRF), in order to verify the occurrence of bromine, with Fiber Optic Reflectance Spectrophotometry (FORS) and Spectrofluorimetry in order to identify dyes. The results suggest that the presence of Tyrian purple cannot be ascertained; if present, it is only a minor component. The most important contribution to the purple colour of parchment is in fact inferred by orchil or folium.