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Updated: Mar 22, 2026

A Colorimetric Method for Measuring Iron Content in Plants
Published on: September 7, 2018
Elucidation of the Fe(III) Gallate Structure in Historical Iron Gall Ink
Aldo Ponce1, Lynn B Brostoff2, Sarah K Gibbons1
1Department of Chemistry and Biochemistry, University of Maryland , College Park, Maryland 20742, United States.
Abstract:
Synthetic, structural, spectroscopic and aging studies conclusively show that the main colorant of historical iron gall ink (IGI) is an amorphous form of Fe(III) gallate·xH2O (x = ∼1.5-3.2). Comparisons between experimental samples and historical documents, including an 18th century hand-written manuscript by George Washington, by IR and Raman spectroscopy, XRD, X-ray photoelectron spectroscopy, and Mössbauer spectroscopy confirm the relationship between the model and authentic samples. These studies settle controversy in the cultural heritage field, where an alternative structure for Fe(III) gallate has been commonly cited.
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