| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 1229168 | Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy | 2015 | 10 Pages |
•Non-invasive and micro-invasive techniques used for folium/orchil identification.•Diagnostic information on these dyes strongly increased.•Historical reconstructions performed in order to have reliable standards.•Evidence that bromine is not a key marker exclusive for Tyrian purple.•Most folium spectral features presented for the first time in a scientific work.
Folium and orchil are dyes of vegetal origin. Folium is obtained from Chrozophora tinctoria (L.) A. Juss., whereas orchil is obtained from Roccella and other genera of lichens. These dyes were used in the past to impart purple hue to paintings and textiles as substitutes for the more prised Tyrian purple dye, obtained from shellfish. Despite several citations in ancient technical treatises dating back at least to the Greek-Roman age, the identification of these dyes in artworks is rare. In the case of folium, an additional drawback is that its composition is presently unknown.In this work different non-invasive (FT-IR, FT-Raman, fibre optic reflectance spectrophotometry, spectrofluorimetry, X-ray fluorescence spectrometry) and micro-invasive (surface enhanced Raman spectroscopy, matrix assisted laser desorption ionisation-time of flight-mass spectrometry, inductively coupled plasma-mass spectrometry) techniques were used in order to increase the diagnostic information available on these dyes. Measurements were carried out on the dyes extracted from raw materials and on painted or dyed parchments. The possibility to distinguish between folium and orchil by chemical analysis is discussed.
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