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

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.