MCI Project Summaries 2008 - Smithsonian Institution

Kα
MCI 6197 Characterization of Iron-Oxide Pigments
MCI Staff: Lynn B. Brostoff, Fabien Pottier, Judy Watson
The goal of this project was to obtain a better general understanding of the composition
and structure of iron oxide-based pigments, as typically encountered in works of art and historic
artifacts, and to optimize the analytical processes for their characterization, especially by XRD.
The first step was to analyze pure commercial pigments and other references, via different
techniques, and compare the results to literature and other published databases. This gave
information about the amount of iron oxides, their crystallinity level, and their nature. It also
permitted characterization of the whole matrices in which iron oxide pigments are typically
found. Once the best conditions and instrumental parameters were determined, and the pigments
were well characterized, the next step was to use these methods to analyze more complex
samples such as rocks, hand-made artist pigments, as well as paint flakes and pottery sherds and
to apply these analyses to conservations issues.
Iron oxides are a widely used family of pigments since ancient times, partly due to their
availability in geological formations everywhere in the world. They can also be prepared simply
by grinding, without complex processes. Therefore, they are very common in artists' materials.
Identification of pigments and other artists' materials allow us to better understand artists'
practices, as well as to understand the history of art technologies.
XRD is a useful method to analyze solid, crystalline samples, since the technique yields
information about the specific identity of the materials. However, iron oxides are not always very
well crystallized, and therefore can be difficult to analyze by XRD. In addition, this method is
subject to interferences, since common compounds such as quartz, calcite and gypsum, which are
often present in natural and synthetic pigments, are very good X - ray scatterers and may
overwhelm the patterns and/or overlap with peaks from the material of interest. Therefore it is
important to fully understand the composition of the whole potential matrices, as well as to
determine the capabilities of this method.
KαC
73
KαC