Mythic dyes or mythic colour? New insight into the use of purple dyes on codices

The traditional knowledge concerning the use of Tyrian purple must be most probably updated in the view of new analytical evidences. With particular respect to purple codices, i.e. the precious biblical texts written with noble metal inks on parchment dyed or painted with purple colorants, measurements carried out in the last years evidenced that this highly-renowned colourant has not, if ever, been used in the making. Non-invasive analysis has been performed in some cases [1-3] and in one case only invasive analysis has been used [4]; in all instance the use of lesser values dyes, such as folium and orchil, has been suggested. Recently, new insight has been given by micro-invasive analysis performed on a fragment of purple parchment taken from the Codex Brixianus (Brescia, Biblioteca Queriniana), a VI century purple codex produced in Gothic realm. Powerful analytical techniques such as Raman-SERS, MALDI-TOF-MS and HPLC-MS could be applied to the analysis of extracts obtained from parchment. Historical reconstructions of dyes according to the ancient recipes have been performed, allowing preparing dyed and painted standards. Roccella tinctoria, Ochrolechia tartarea and other lichen species were used to prepare orchil, while Chrozophora tinctoria fruits were used to prepare folium. A particular feature of these materials, evidence by XRF analysis, was the non-negligible content of bromine possibly related, in the case of lichens, with the exposure to sea-spray. The results of micro-invasive analysis confirmed once more that Tyrian purple was not the dye used on purple codices and that both orchil and folium were used instead.