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• xH 2 O (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 Comparisons between experimental samples and historical documents, including an 18th century hand-written manuscript by George Washington, by IR and Raman spectroscopy, XRD, X-ray photoelectron spectroscopy, and Mossbauer 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.P rior to the 20th century, historical iron gall ink (IGI) was by far the most common writing material of the western world, and a plethora of recipes from which to produce the ubiquitous dark, brown-black ink can be found starting from at least the Middle Ages. This ink has been used to pen many of the most important documents and drawings in human history, including unique, hand-written works such as Thomas Jefferson's original draft of the Declaration of Independence, Abraham Lincoln's first draft of the Emancipation Proclamation, and Beethoven's original scores. While the virtue of IGI lies in its relative permanence, the great vice of this medium lies in its well-known tendency to degrade paper and parchment substrates. 1−7 Despite its historical importance, there is little consensus on the chemical structure or composition of the iron-gallate complex, the main species responsible for the color of the IGI. We describe here a series of synthetic, structural, spectroscopic, and aging studies, which unequivocally demonstrate that the primary colorant in IGI is an amorphous form of an octahedral Fe(III) gallate metal organic framework structure that has previously been described by Wunderlich 8−10 and Feller. 11 Unlike the majority of prior studies, we use authentic IGI precursors to prepare both crystalline and amorphous forms of the IGI precipitate and study the crystal-to-amorphous transition by way of XRD, thermal gravimetric analysis (TGA), IR and Raman, Mossbauer, and X-ray photoelectron spectroscopy (XPS). Spectroscopic comparisons with historical documents prove the relevance of the synthetic crystalline and amorphous forms of the model IGI materials to those found in the authentic manuscripts.

X-ray diffraction (XRD) complemented by Raman spectroscopy analyses of synthetic organic pigments in powder samples, layered paint systems, and commercial artists’ paints bound in acrylic, alkyd, and oil media are presented. The potential and limitations of the techniques to identify and characterize mixtures of these pigments, along with inorganic extenders, in works of art are exemplified and discussed. Stratified model paint systems that mimic the layering structure typically found in modern paintings are used to evaluate the effect of the μXRD experimental parameters, as well as extenders or fillers commonly found in modern artists’ paint formulations, on the quality of the patterns recorded in microsamples of paint. XRD is demonstrated for the first time to be an effective tool for the specific identification of synthetic organic pigment mixtures and fillers in acrylic and alkyd bound artists’ paints, while the identification of these pigments by XRD in oil bound paints appears problematic. Detailed crystallographic information provided by XRD is shown to be complementary to molecular information provided by Raman analysis. The combined use of these techniques allows for more frequent unambiguous compound identification than would be possible using one technique alone.

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