Iron gall inks and their preservation – case study: 16th century documents in the Archivo Histórico Provincial de Santa Cruz de Tenerife

Iron gall inks were used for centuries, which is why most institutions keep a multitude of manuscripts with this type of ink. The main problem that affects these artefacts is corrosion due to the ink composition. The main objective of this paper is to define an inspection protocol for documents from the 16th century found in the Archivo Histórico Provincial de Santa Cruz de Tenerife, which can also be applied to similar manuscripts. This protocol involves the inspection of each document with diffuse and transmitted visible light, UV radiation and digital optical microscopy. In addition, a Kodak Gray Scale was used to evaluate the colour depth of the inks. This inspection indicates that a significant proportion of the documents analysed are in condition 3 and 4, meaning in poor and bad condition, which indicates a high level of vulnerability.