Evidence for the degradation of an alloy pigment on an ancient Italian manuscript

Abstract

An unusual metallic pigment was identified on an ancient Italian manuscript containing the Homilies on the Gospels of Gregory the Great, belonging to the Archive and Chapter Library of Vercelli (Italy) and datable to the IX century. Green uncial text and part of decoration on this manuscript were described as 'being of golden fashion' in a book written at the beginning of XX century. Investigations carried out with portable XRF and Raman instruments revealed that the green colouration is actually the result of a marked degradation process that has altered the original composition of the pigment, an alloy of copper, lead and zinc. Probably because of the conditions of storage of the manuscript, the pigment tarnished owing a chemical process that could resemble the infamous 'bronze disease': that is, the conversion of metallic copper into inorganic salts. Measurements were performed both in situ, i.e. directly on the manuscript, and on small fragments of ink collected from the page gutters.

Raman spectroscopy in art and archaeology

“…The next motivation is for the study of partly or highly damaged materials in an attempt to get a better idea of the original object, as is illustrated with a pigment identification. 62 Degradation of numerous materials has been explored, from organic to mineral. Studies on the degradation of waterlogged wood and optimisation of their conservation treatments are presented.…”

Forgery detection on an Arabic illuminated manuscript by micro‐Raman and X‐ray fluorescence spectroscopy

“…The most likely reason would be the presence of calcium carbonate, produced from the carbonation of lime, which is usually employed in parchment manufacture. [6,9] A common observation in all the coloured zones studied by XRF was the presence of calcium, titanium and zinc, and also barium in almost all cases. Elemental analysis by the XRF technique is difficult in the case of illuminated manuscripts, which comprise a superimposition of coloured layers on a paper support.…”

Raman Spectroscopy of cultural heritage Materials: Overview of Applications and New Frontiers in Instrumentation, Sampling Modalities, and Data Processing

“…This technical advancement allowed the reaching of several milestones: (1) it enabled micro-analysis (and, subsequently, imaging), (2) it allowed the focusing of the excitation power (thus cutting out the need for powerful lasers), and (3) it led to significant improvements in the collection of Raman scattering thanks to the high numeric aperture of microscope objectives. Using microscope objectives, analysis at the micron scale can be easily achieved, a very interesting possibility for studying ancient samples, which are typically highly heterogeneous.…”