We tested our calibration on several silicate glasses equilibrated under moderately reducing conditions (QFM+0.8 ≤ fO2 ≤ QFM+1.4) in which S is dissolved as both SO42– and S2–. We also analyzed several olivine-hosted melt inclusions collected from Etna for which the fO2 and S speciation are unknown. For these samples, the S content estimated by the Raman calibration is systematically lower than the total S measured by EPMA. We combined both methods to estimate the S2– content not accounted for by Raman and derive the S speciation and fO2 conditions. The derived fO2 is consistent with the imposed fO2 for synthesized glasses and with current assumed fO2 conditions for basaltic melt inclusions from Etna.