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This project examines iron gall ink crystals within drawings in the collection of the Department of Prints, Drawings and Photographs of the Museum of Fine Arts, Boston and selected additional collections with particular interest in the works of Jan de Bisschop, Giovanni Domenico Tiepolo, and Jean-François Millet. Ink crystals range in color from white or gray to yellow-orange, bear a variety of shapes, and can most often be observed on drawings where a substantial quantity of ink remains atop the surface of the paper. Instrumental analysis by X-ray fluorescence, scanning electron microscopy, electron dispersive spectroscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy identified the chemistry of the crystalline material as sulfates, primarily of iron. The role of ink composition and environment in the formation of these crystals was explored through accelerated aging of twelve sets of fabricated ink samples. Each set consisted of twenty ink mixtures with distinct ratios of iron sulfate to gall nuts to gum arabic binder. Experimentation revealed an increased frequency of crystallization upon aging with samples containing high iron sulfate concentrations and minimal gum binder.
Deborah La Camera (Mon,) studied this question.