Assessment of Ethanol-modified Phytate-bicarbonate Treatment for Water-sensitive Iron Gall Inks

This research evaluates the performance of ethanol-modified phytate-bicarbonate treatments in slowing the iron gall ink-induced degradation of paper, to provide conservators with a better understanding of treatment options for water-sensitive iron gall ink documents. To date, ethanol-modified phytate-bicarbonate protocols have yielded promising results, based on empirical observations; however, questions have arisen about treatment efficacy and precipitate formation in ethanol-modified phytate solutions. The study compares multiple ethanol-modified magnesium phytate-calcium bicarbonate treatments with two ethanol-modified calcium phytate-calcium bicarbonate treatments of model iron gall ink on sized rag paper. Ethanol-modified water washing alone is included for comparison. The relative effect of different treatment parameters, namely percentage of ethanol in solutions, phytate concentration, and pH of magnesium phytate, is assessed by linked visual and chemical analyses, including color of ink and paper, surface deposits, iron(II) testing, micro x-ray fluorescence elemental mapping, pH, and size exclusion chromatography. Results demonstrate that ethanol-modified magnesium or calcium phytate paired with calcium bicarbonate are both viable options for combating iron-induced oxidation and acid hydrolysis of the cellulose in artifacts with water-sensitive iron gall ink, assuming pre-treatment testing does not reveal solubility of the ink in the selected solvents.