Identification of copper carboxylates as degradation residues on an ancientmanuscript

Copper carboxylates were identified as degradation residues on the surfaceof a metallic pigment used in the illumination and in the text of a 9th centuryItalian manuscript containing the Homilies on the Gospels of Gregory the Great,belonging to the Archive and Chapter Library of Vercelli (Italy). Thesecompounds are responsible of the greenish aspect that several text lines anddecorated initials have developed over time from their original golden texture,starting from more than a century as could be guessed from the early 20thcentury descriptions of the manuscript by art historians. Further, Ramaninvestigations carried out on a particle recovered from the gutters betweenfolios allowed (1) the identification with good accuracy of the nature of thesecompounds, confirmed by scanning electron microscopy-energy dispersive X-ray(SEM-EDX) analysis, (2) proposing a hypothesis on their origin as due to theinteraction of copper with carboxylic acids and (3) making suggestions on theproper restoration intervention; moreover, evidence was found for similarcompounds in three 9th-10th century Italian manuscripts coming from Bobbioabbey. Besides, the presence of orpiment in ink composition was verified andcompared with citations in some medieval texts.