Late production of Egyptian blue: synthesis from brass and its characteristics

Abstract

This work follows the recent discovery of a zinc-bearing Egyptian Blue (EB) pigment widely used for the production of the early medieval mural paintings cycle in Santa Maria foris portas church at Castelseprio (Lombardy Region, Italy).The inclusion of zinc in the synthesis of EB has been studied for the first time trying to evaluate whether its addition could be casual or deliberate. Historical reconstructions of the pigment have been carried out with a special focus on the use of zinc besides copper, using different production methods. The influence of zinc on the pigment's NIR photoluminescence and VIS-NIR reflectance has been characterized using FORS spectroscopy, X-Ray diffraction, optical microscopy, Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy. A comparison of production methods including salt-flux, solid state and Zn-rich syntheses showed that solid-state synthesis results in particularly efficient NIR photoluminescence and VIS-NIR reflectance. Modern replicas were compared to an ancient sample in order to understand the zinc environment inside the structure of the Zn-enriched EB. Zn was found to be concentrated in a glass-based matrix surrounding cuprorivaite crystals, the main mineral associated with the EB pigment, and not included in a Zn-doped cuprorivaite with formula CaCu 1-x Zn x Si 4 O 10. The Zn-rich synthesis opens up the possibility of producing EB from brass and demonstrates that EB used in Castelseprio's mural paintings could have been produced in this way. The relationship between the microstructure and the NIR photoluminescence of cuprorivaite-like pigments is of interest also for applications in modern and future technologies.

Egyptian Blue Pellets from the First Century BCE Workshop of Kos (Greece): Microanalytical Investigation by Optical Microscopy, Scanning Electron Microscopy-X-ray Energy Dispersive Spectroscopy and Micro-Raman Spectroscopy

“…Based on elemental analysis, arsenical copper alloys have been identified as the copper source for Egyptian blue production in the Old Kingdom, which was replaced by bronze scrap from the second half of the second millennium BCE and until the Roman period [1,41,50]. Later Egyptian blue productions indicate the use of brass (copper-zinc alloy) for the production of Egyptian blue [69]. These observations suggest a preference for the use of copper alloys instead of metallic copper or copper ores for the production of Egyptian blue.…”

Preparation, properties and applications of near-infrared fluorescent silicate nanosheets

“…the well-known Bust of Queen Nefertiti). [49][50][51][52][53] HB and HP, on the other side, were mostly employed in the times of the Qin and Han dynasties (≈220 BC-220 AD), as witnessed by e.g. the Terracotta Warriors of the tomb of Emperor Qin Shihuangdi in Xi'an.…”

Covalently Functionalized Egyptian Blue Nanosheets for Near-Infrared Bioimaging

“…Previous works have demonstrated that silanol groups are indeed accessible in significantly high numbers as a consequence of both synthesis and exfoliation procedures 22,35,73 . Our goal was to first demonstrate that this chemistry works in general and then to use it to bind biologically relevant molecules to EB-NS.…”