Characterization of green copper phase pigments in Egyptian artifacts with X-ray absorption spectroscopy and principal components analysis

Abstract

The characterization of materials in historical artifacts can contribute significantly to their preservation and understanding; however, sampling and characterization are ideally performed using non-destructive approaches. The analysis of green pigments from Egyptian artifacts presents a further challenge as responses to laboratory based techniques have proven unsuccessful in many cases. An alternative approach is the use of non-destructive X-ray absorption near-edge structure spectroscopy, which was performed on a reference set of copper-containing green minerals and other compounds. Data projection using principal component analysis was used to explore the spectral data structures and to illustrate the relationship between the spectra and copper speciation, resulting in a calibration or training set of the reference materials used. Data from the training set were compared with samples from Egyptian artifacts. The combination of X-ray absorption spectroscopy with principal components analysis provides a novel approach in archeometry and the characterization of objects of cultural heritage.Crown

On the stability of mediaeval inorganic pigments: a literature review of the effect of climate, material selection, biological activity, analysis and conservation treatments

“…Unstable, blackening upon light exposure [1,64] Involved in discolouration [93,245] Whitening [68, 93, Green discolouration [156][157][158] Green discolouration [156][157][158] - [28] - [28] Black …”

“…ions are leached and react with Cl − ions from the glass itself or from circulating solutions to form carbonates and chlorides [156][157][158]. Degraded Egyptian blue was found to contain chlorides (atacamite and eriochalcite CuCl 2 ·2H 2 O) [158].…”

“…Degraded Egyptian blue was found to contain chlorides (atacamite and eriochalcite CuCl 2 ·2H 2 O) [158]. Moreover, the yellowing/darkening of the organic materials (varnishes, gums) can alter the appearance of this blue pigment, and pigment-binder interactions could promote selective darkening, thanks to the release of copper ions from the pigment itself, possibly in relation to pH, impurities and gum type [155].…”

“…As a pigment, it can be natural or synthetic, and the particles' morphology and composition can clarify its origin [162,164]. It is expected to form as a degradation product of Cu containing pigments, or artefacts such as bronzes, in presence of humidity and chloride anions [115,119,121,158,160,165,166]. It is however not stable in acidic conditions (oxalic acid, for example), which promotes the formation of mooloite (CuC 2 O 4 ·nH 2 O) [127].…”

Characterization and Examination of Pigments, Grounds and Media From Ancient Egyptian Cartonnage

“…(7). The principal red pigments in Egypt are of two main types, red iron oxide (hematite) and red ochre (hydrated) [25]. Natural iron oxides occur plentifully in Egypt and then anhydrous and hydrated oxides could be used as red pigments without any heat treatment.…”