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Orchil is a purple dye extracted from lichens, widely used since the 6th century for dyeing parchments, yarns and textiles, in particular as a substitute for the rare and expensive Tyrian Purple dye; additionally, it was used as a colourant in illuminated manuscripts. The dye was produced since antiquity, through a slow process which could take three weeks or more, by soaking lichens in ammonia in order to promote the transformation of the chemical precursors into a mixture of phenoxazonic compounds, collectively known as orceins. Orchil can be obtained from different lichen species, which are native to specific regions or geographical areas. Since each species can have a typical set of chemical precursors, the final set of orceins could be characteristic of the relative species, even if the macroscopic features of the dye would be similar in terms of hue and spectral responses upon analysis. In this work, a preliminary study is carried out in order to try to identify a diagnostic pattern of three common lichen species (Lasallia pustulata, Ochrolechia tartarea, Roccella tinctoria) by means of HPLC-MS/MS analysis, so as to develop a tool useful to identify the origin of real samples dyed with orchil, among which are featured textiles and purple parchments from ancient manuscripts. Such identification may be exploited in order to assess the relationship between an artwork and the geographical origin of its raw materials.

The Privilegium maius is one of the most famous and spectacular forgeries in medieval Europe. It is a set of charters made in the 14th century upon commitment by Duke Rudolf IV, a member of the Habsburg family, to elevate the rank and the prestige of his family. These five charters, now kept at the Österreichisches Staatsarchiv in Vienna, have been subjected to a thorough interdisciplinary study in order to shed light on its controversial story. The charters are composed of pergamenaceous documents bound to wax seals with coloured textile threads. The present contribution concerns the characterisation of the inks used for writing and of the dyes used to colour to the threads: Are they compatible with the presumed age of the charters? Though showing only a part of the whole story of the charters, dyes analysis could contribute in assessing their complex history from manufacturing to nowadays. The dyes were characterised with non-invasive in situ measurements by means of fibre optic (FORS) and with micro-invasive measurements by means of Surface Enhanced Raman Spectroscopy (SERS) and High-Performance Liquid Chromatography with Mass Spectrometry (HPLC-MS) analysis. The results showed that the threads of four of the charters (three dyed with madder, one with orchil) were apparently coloured at different dyeing stages, then re-dyed in the 19–20th century.