Caren Sullivan–October 21, 2015

This past week I unfortunately have not been able to be in the lab much as I was studying for the GRE (which I am taking tomorrow morning!). However, I did some research on the chemistry behind my iron gall ink synthesis/fermentation. I found that gum arabic (the binder) is a bipolymer of arabinose and galactose monosaccharides, making its chemistry extremely close to that of sugar. Furthermore, after reading the “IGI (Iron Gall Ink) Chemistry” section on http://www.irongallink.org/ and using the Library of Congress Database, I was able to find much regarding the chemistry of the reaction, although there is still much unknown. It seems that the initial grey/black color of the ink comes from the iron ions (in the vitriol, or iron (II) sulfate) reacting with the oxygen present in the solvent (water, vinegar, etc.), producing this color. The iron ions also may complex with the oxygen atoms available off of gallic acid’s (from the oak galls) benzene ring, increasing the color as well. Over time, as the inks (or, specifically the iron ions) are exposed to more oxygen, this color will darken to black. The oak galls themselves consist of gallotannic acid, but over time–either during the fermentation process or from oxygen exposure–the gallotannic acid releases gallic acid. This is apparent especially if any mold forms on the surface of the ink, which I actually saw in the early stages of the fermentation. This is also extremely important as gallic acid is the key component regarding iron gall ink’s degradation over time–which I actually hope to recreate as we are seeing something similar in the manuscript. Overall, after reading these articles, I am much more certain regarding the chemistry behind my iron gall ink synthesis. This upcoming week I plan to characterize my inks through IR, Raman, and UV-Vis Spectroscopy in an attempt to confirm the chemistry that should have happened in my own reaction according to the sources above. I also plan to further investigate the chemistry in the reaction as there is always more to learn! For example, I plan to research the Raman active bands of iron gall ink and the signatures of the individual components present such that I can fully analyze my spectra.

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