Degradation mechanisms of Indian banks promissory notes written in iron‐gall inks and its conservation

Abstract

The objective of this study is to investigate the deterioration of 18th‐century Indian Bank's Promissory Notes written using iron‐gall ink. The research employs non‐destructive techniques such as Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD) and scanning electron microscopy (SEM) with energy‐dispersive X‐ray spectroscopy to analyze the elemental composition and structural characteristics of both the iron‐gall ink and the paper support. The analytical findings indicate that the acid hydrolysis of the iron‐gall ink complex has led to corrosion and weakening of the document. The reactivity of Fe3+ ions, indirectly assessed through XRD analysis by measuring the crystalline index (Crl) of the paper, indicates a loss of strength in the cellulose fibers. The combination of FTIR and XRD data also reveals the utilization of gypsum as a filler in the paper, likely intended to enhance its gloss and opacity. SEM photomicrographs further illustrate the presence of iron crystals on the paper surface, a result of the non‐uniform distribution of the ink and oxidation of ferrous ions also supported by surface mapping of iron. The paper's composition is identified as cellulose I, a common variety found in nature. These findings collectively provide insights into the degradation processes affecting both the iron‐gall ink and the paper support. The innovative calcium phytate treatment was applied for document conservation.