Variable-Temperature and High-Pressure Micro-Raman Spectra of Inorganic Artists' Pigments: Crystalline Wulfenite, Lead(II) Molybdate(VI), PbMoO4

Variable-temperature (-150 degrees C to 600 degrees C) and high-pressure (up to similar to 5GPa) micro-Raman spectra have been obtained for the mineral wulfenite [lead(II) molybdate(VI), PbMoO4], a main constituent of the artists' pigment, orange molybdate. The spectra were quite similar in both the temperature and the pressure studies, except for broadening and shifting of some peaks. No phase changes were detected, although there is possibly some amorphization beginning at similar to 600 degrees C. The photoacoustic IR spectrum in the 1950-450cm(-1) region is reported for characterization purposes. The long-term stability of PbMoO4 with respect to extreme changes in both temperature and pressure illustrates the importance of orange molybdate in artwork and protective coatings.