A holistic approach to understanding the iron-gall inks in the historical documents of the Portuguese Inquisition (1570-1790)

A substantial part of our written heritage is threatened by the fact that much of it has been written using iron-gall ink (IGI). One such example is the documents of the Portuguese Inquisition Tribunals, held by the Arquivo Nacional da Torre do Tombo. Here we present the first systematic analytical approach, using SEM/EDS, µ-FT-IR-ATR and µ-Raman techniques, to characterise fragments from historical records of the Inquisition Tribunals of Évora, Lisboa and Coimbra from the 16th to 18th centuries. The writing ink was identified as IGI, providing complementary compositional data and establishing differences between various formulations of the ink. Additionally, the deleterious effects of the inks-associated degradation phenomena were highlighted. This work allowed understand the writing inks used by this Portuguese institution.