Flux growth and characterization of cuprorivaite: the influence of temperature, flux, and silica source

Abstract

Single crystals of cuprorivaite (CaCuSi 4 O 10 ), one of the oldest synthetic color pigments of Egyptian history, have been synthesized by slow-cooling flux method. Several runs were carried out at temperatures between 800 and 960°C and with reaction times ranging from 10 to 72 h. The starting materials and run products were characterized by binocular microscope, X-ray powder diffraction, scanning electron microscopy with annexed energy-dispersive spectrometry, and l-Raman spectroscopy. The effects of growth parameters (temperature, flux, silica source) on yield and size of crystals were studied. The growth of cuprorivaite depends greatly on the starting materials: they are observed as run products only using natron as flux. Furthermore, colorimetric analysis performed on the synthesizing pigment was compared with the archeological samples present in the literature in order to value similarities and differences.

Non-Destructive Multi-Analytical Approach to Study the Pigments of Wall Painting Fragments Reused in Mortars from the Archaeological Site of Pompeii (Italy)

“…Figure 8a,b show two blue euhedral cuprorivaite crystals (CaCuSi 4 O 10 ) detected by Raman spectroscopy. Indeed, the relative spectra show typical cuprorivaite bands at 113, 137, 361, 377, 431, 568, and 1083 cm −1 [40,[51][52][53][54][55][56]. Cuprorivaite, which is a calcium-copper tetrasilicate, is the main component of ancient Egyptian blue pigment [57], a synthetic pigment obtained by heating a mixture composed of calcite, siliceous sand, copper compounds, and natron or plant ash, to a temperature ranging between 850 • C and 950 • C [52,58,59].…”

Archaeometric Approach for Studying Architectural Earthenwares from the Archaeological Site of S. Omobono (Rome-Italy)

“…The scans were collected with a step scan of 0.02 • 2θ and 2 s/step, in the range 3-60 • 2θ. The width of the divergence, anti-scattering and receiving slits were of 0.6, 0.2, and 0.1 mm, respectively [43]. To identify the mineralogical phases in each X-ray powder spectrum, DIFFRACplus EVA V. 11.3 software program (Bruker, Karlsruhe, Germany) was used, by comparing experimental peaks with PDF2 reference patterns.…”

Mechanical ordering of pigment crystallites in oil binder: Can EPR reveal the gesture of an artist?

“…A possible explanation for this preferred orientation is based on the sedimentation of the pigment crystallites within the oil while the latter is still viscous. Indeed, microcrystals of cuprorivaite exhibit a tabular morphology (Bloise, et al, 2016). Then when microcrystals fall through the liquid oil under the gravitational force, they tend to lay down with their largest face horizontal (Fig.…”