Identification of CaCuSi$_4$O$_{10}$ (Egyptian blue) in the "Birch. Spring" painting by Robert Falk (1907) using photoluminescence

Abstract

We have detected Egyptian blue pigment in the paint layer of the "Birch. Spring" painting by Robert Falk (1907); we have also found this pigment in the paints of the sketch drawn on the canvas back side. This is probably the first discovery of Egyptian blue in a 20th century work of art. We have analyzed a modern commercial Egyptian blue pigment (Kremer) and found it to be suitable as a standard for photoluminescence spectral analysis. The characteristic photoluminescence band of CaCuSi$_4$O$_{10}$ reaches maximum at the wavelength of about 910 nm. The luminescence is efficiently excited by incoherent green or blue light. The study demonstrates that the photoluminescence spectral micro analysis using excitation by incoherent light can be efficiently used for the identification of luminescent pigments in paint layers of artworks.