Abstract

Prussian blue, a hydrated iron(III) hexacyanoferrate(II) complex, is a synthetic pigment discovered in Berlin in 1704. Because of both its highly intense color and its low cost, Prussian blue was widely used as a pigment in paintings until the 1970s. The early preparative methods were rapidly recognized as a contributory factor in the fading of the pigment, a fading already known by the mid-eighteenth century. Herein two typical eighteenth-century empirical recipes have been reproduced and the resulting pigment analyzed to better understand the reasons for this fading. X-ray absorption and Mössbauer spectroscopy indicated that the early syntheses lead to Prussian blue together with variable amounts of an undesirable iron(III) product. Pair distribution functional analysis confirmed the presence of nanocrystalline ferrihydrite, Fe10O14(OH)2, and also identified the presence of alumina hydrate, Al10O14(OH)2, with a particle size of ~15 Å. Paint layers prepared from these pigments subjected to accelerated light exposure showed a tendency to turn green, a tendency that was often reported in eighteenth-and nineteenth-century books. The presence of particles of hydrous iron(III) oxides was also observed in a genuine eighteenth-century Prussian blue sample obtained from a polychrome sculpture.

Department(s)

Chemistry

Keywords and Phrases

Alumina; Archaeometry; Chemistry; Colorimetry; Equipment Design; Equipment Failure; Equipment Failure Analysis; Ferric Ferrocyanide; Ferrocyanide; Hexacyanoferrates; Hydrates; Hydration; Iron(III) Hexacyanoferrate(II); Light Exposure; Light Exposure Fading; Materials Testing; Paint Layers; Pair Distribution Function; Spectrometry; Synchrotron; X Ray Diffraction; X-Ray Emission

International Standard Serial Number (ISSN)

0909-0495

Document Type

Article - Journal

Document Version

Final Version

File Type

text

Language(s)

English

Rights

© 2013 International Union of Crystallography (IUCr), All rights reserved.

Publication Date

01 May 2013

Included in

Chemistry Commons

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