Egyptian Blue: variability in production technology, material provenance and deterioration

Egyptian Blue: variability in production technology,  material provenance and deterioration 

Eva Luna Ravan(1,2), Francesco Paolo Romano(2), Ariadne Kostomitsopoulou 
Marketou(3), Fani Pinakidou(4), Kalliopi Tsampa(5), Andreas Germanos 
Karydas(5), Hariclia Brecoulaki(6), and Claudia Caliri(2) 

(1) Sapienza University of Rome, Piazzale A.Moro 5, 00185 Rome, (Italy) 
(2) CNR-ISPC, Via Biblioteca 4, 95124, Catania, Italy  
(3) MF Norwegian School of Theology, Religion and Society, Oslo, Norway 
(4) School of Physics, Aristotle University of Thessaloniki, Thessaloniki, Greece 
(5) Institute of Nuclear and Particle Physics, NCSR “Demokritos”, Athens, Greece 
(6) Institute of Historical Research, National Hellenic Research Foundation, Athens, Greece 

Egyptian Blue (EB), one of the most commonly used pigment in antiquity, served as the primary 
blue pigment in artists' palettes until the 4th century CE [1] and in rare cases beyond. Its 
distinctive color derives from the orientation of copper (II) in the copper calcium tetrasilicate 
crystals (CaCuSi4O10, its naturally occurring but rare counterpart is the mineral cuprorivaite) 
[2]. Nonetheless, EB is a multicomponent material, the variability in its color, that can range 
from dark blue to almost white, can be attributed to differences in grain size, proportions of 
various mineral phases in the final product and manufacturing technology [3]. In our study we 
adopted a non-destructive multi-modal methodology, incorporating mobile analytical X-ray 
techniques, to analyze EB samples sourced from a variety of well-documented archaeological 
sites. The investigation encompassed wall painting fragments from late Classical and early 
Hellenistic Macedonian tombs. We have combined high-resolution 2D micro-XRF imaging 
(MXRF), 3D Confocal XRF mapping (CXRF) and 1D X-Ray Powder Diffraction (XRPD) 
available in the MOLAB platform of E-RIHS (ISPC-CNR, Catania, Italy). The non-destructive 
nature of this approach allowed for a thorough examination of the samples, yielding 
comprehensive analytical data. The findings offer deep insight into the choice of source 
materials, as evidenced by the XRF elemental analysis, and elucidate the crystalline 
environment of Cu-based pigments through XRPD. The use of micro-XRF imaging and 3D 
confocal XRF applied to the wall paintings fragments provides useful insights on the original 
painting techniques. The results of our research enable a better understanding of material 
provenance, technological changes, and the identification of ongoing deterioration 
mechanisms. 

[1] P. García-Fernandez, M. Moreno, J.A. Aramburu, J. Chem. Educ. 2016, 93, 111-117.  
[2] V. Daniels, R. Stacey, A. Middleton, Studies in Conservation 2004, 49:4, 217-230.  
[3] A. Kostomitsopoulou, F. Giannici, F. Caruso, Anal. Chem. 2021, 93, 11557-11567.