Painted plaster and glazed brick fragments from Achaemenid Pasargadae and Persepolis, Iran

Background: Architectural fragments of decorated walls, floors, and columns excavated by Ernst Herzfeld (1879-1948) at the archaeological sites of Persepolis and Pasargadae in Iran are housed in the Freer Study Collection at the Freer Gallery of Art and Arthur M. Sackler Gallery (FSG), Smithsonian Institution in Washington, DC. Technical studies of these painted earthen plasters and glazed brick fragments were undertaken to enhance our knowledge of materials and technology of Achaemenid Persia between the late sixth and fourth centuries BCE. Initial analysis was done on the surface of the fragments using non-invasive X-ray fluorescence with a portable instrument. Polished cross-sections were used to examine the layering stratigraphy of paints and glazes, and to undertake compositional analysis using scanning electron microscopy with energy-dispersive X-ray spectroscopy. Results: Up to five layers of paint are present on the Pasargadae plaster, constituting the remnants of a geometric design. The plasters were bound with clay tempered with an organic material that has long since degraded, leaving small voids throughout. Pigments identified include Egyptian blue, malachite green, red ocher, and cinnabar red. The floor fragments from Persepolis were finished with a lime plaster and two layers of hematite-rich paint. The brick fragments from Persepolis were found to be composed of high-silica material similar to faience, which were decorated with alkaline glazes, including a yellow glazed colored with lead antimonate, gray glaze colored with magnesium and iron, and green glazed colored with copper. Conclusions: While the exact ages of the finishes are unknown, a similar technology was employed to decorate Achaemenid architecture in its principle Iranian cities. The variety of materials excavated by Herzfeld demonstrates the ability of Achaemenid artisans to work with multiple mediums to create a polychromatic finish including that of glazed tiles, earthen plaster tempered with gravel, earthen plaster tempered with organic matter, colored earths, pigmented paints and lime plasters. The layering of these materials can be seen and analyzed in cross-section although surface deterioration is often quite severe. The analysis of the compositional data on the architectural fragments inform their long-term preservation at the FSG as well as at the sites themselves.