The monumental architecture of Middle Eastern cities was characterized between the 14th and 4th centuries BC by the use of colored glazed bricks. The production of this kind of decoration required thorough knowledge and important resources, in a societal context favorable to invention and exchange. The regions of production of these bricks moved throughout history between the Mesopotamian alluvial plain and the Iranian world. However, the share of knowledge and local innovations that took place in this geographical space is not clearly defined.
The present piece of research focused on the brick production practices by inspecting colored glazes. Among the numerous colors of these decorations, we concentrated on the yellow-orange range, colored by lead antimonates. In this work, a double approach was conducted in parallel. A first step involved multi-scale characterizations of well-preserved yellow-orange glazes of colored bricks representative of the decoration of the Sargon (Khorsabad, 8th century BC) and Darius (Susa, 6th century BC) palaces. Secondly, replicas of glazes colored by addition of lead antimonates, were synthesized in laboratory under controlled conditions (firing time, temperature, cooling rate). The recipes of these colored glasses were established from the chemical analysis of ancient glazes. By comparing the microstructure and final composition of the synthesized glazes to those of archaeological samples, we can get some clues on technical elements of the production (in particular about the recipes and the firing temperature). The multi-analytical investigation involving chemical (SEM-EDX, PIXE-PIGE and µ-XANES) and mineralogical (XRD and µ-Raman spectroscopy) analysis was performed to characterize both archaeological and replica yellow-orange glazes.
The analysis of ancient glazes of archaeological bricks allowed us to compare the different recipes of yellow-orange colored glazes employed in the Neo-Assyrian and Achaemenid periods. The analyses showed that the samples from Khorsabad and Susa present some differences especially with an addition of hematite and calcium antimonates for the glazes of Khorsabad. The results for both corpuses suggested that the pigment was prepared ex-situ or in the form of “corpo” (i.e. glass very rich in opacifying and coloring crystals) and then, probably mixed with an alkali glass frit. The chemical diversity of the identified antimonates, thanks to the numerous substitutions permitted by their pyrochlore structure (especially antimony with iron and lead with calcium), make them sensitive markers of the chemical, thermal and kinetic conditions in the glazing process. Understanding reactivity and transformations of these pigments during firing gives some precious information in order to reconstruct the history of craftsmanship and the transfer of know-how between the ancient civilizations of the Middle East in Antiquity.