Estudio de tintas en manuscritos antiguos de la Biblioteca Nacional de Colombia por medio del Sistema de Imagen Multiespectral para Artefactos Históricos (MISHA)

Abstract

Within this context, the recent acquisition of the Multispectral Imaging System for Historical Artifacts (MISHA), developed by the Rochester Institute of Technology (RIT), made it possible to propose a study aimed at the non-invasive characterization of inks present in ancient manuscripts from the Rare Manuscripts collection of the National Library of Colombia (BNC). The high heritage value of these documents precludes the use of analytical techniques that require sample extraction. The chemical characterization of these inks poses a considerable challenge, as conventional analytical methods are incompatible with the conservation of unique pieces; moreover, although multispectral image analysis can register optical differences between materials, the spectral response alone does not allow the composition of an ink to be identified without reference standards of known composition. To address this problem, twelve metallogallic reference inks were prepared based on historical formulations, varying the metal salt employed (ferrous sulfate, ferric sulfate, copper sulfate, and mixtures thereof) and the extraction vehicle (distilled water, white wine, and red wine), while keeping constant components such as oak galls and gum arabic. These inks were characterized by high-performance liquid chromatography (HPLC-DAD) and UV-Vis spectrophotometry, and subsequently compared with multispectral captures of selected manuscripts from the collection, processed through Principal Component Analysis (PCA) and the Spectral Angle Mapper (SAM). The results showed that most of the regions analyzed in the manuscripts exhibited a spectral response compatible with the iron-containing reference inks (ferrous sulfate and ferric sulfate), consistent with the historically predominant use of metallogallic inks in the Western writing tradition. It should be noted that this spectral response must be understood as a spectral signature compatible with that of the corresponding reference ink, rather than as a direct chemical identification; accordingly, manuscript regions whose signatures matched one of the twelve reference inks were considered positive on the basis of spectral compatibility, but not as definitive compositional confirmation. The red-colored inks and pigments identified in some manuscripts showed no spectral compatibility with the twelve reference inks developed in this study, suggesting that they correspond to a different type of material not considered in this work. Likewise, some cases were observed in which areas of support deterioration coincided with regions exhibiting a response compatible with iron-based inks, although this does not allow a definitive causal relationship to be established. The MISHA system and the reference ink library built in this work are established as a useful tool for comparing, within a single capture, the spectral response of inks present in historical manuscripts against standards of known composition, without the need to extract samples from the document. Nevertheless, this methodology does not replace, but rather complements, confirmatory analytical techniques, and its combination with such techniques remains necessary to achieve a definitive chemical identification of the inks studied.