This paper investigates, using only Raman spectroscopy, the spectral differences among the synthetic ultramarine blue (J. B. Guimet) and three natural ultramarine blues (lazurites) corresponding to three lapis lazulis from different geographical sources (Chile, Afghanistan and Siberia). The synthetic ultramarine blue used as reference pigment is the identified in an artwork created around 1917 by the Catalonian modernist painter Ramon Casas i Carbó. This synthetic pigment is compared with the three natural ultramarine blues and, in his turn, the latter are also compared each other. In order to quantify the spectral differences, a rigorous methodology based on the Euclidean distance between homologue spectral segments (or intervals) has been developed and presented here.

holds the position of Senior Researcher at the Statistical Inference for Communications and Positioning (SI) Department at CTTC. He received the MSc degree in Telecommunication Engineering from La Salle University in 2004, and the PhD from UPC in 2012. His primary areas of interest include statistical signal processing, GNSS synchronization, detection and estimation theory, software defined receivers, FPGA prototyping and the design of RF front-ends. He is the recipient of the 2015 EURASIP Best PhD Thesis Award. Mr. Antonio Ramos de Torres is a Ph.D Candidate in the Signal Theory and Communications Department of the Universitat Politècnica de Catalunya (UPC). He received the MSc degree in Telecommunication Engineering from UPC in 2013. His primary areas of interest include statistical signal processing with application in spectroscopy analysis techniques and GNSS software defined receivers.

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