This study entailed a dissolution study of alumina fine ceramics in a CaO–Al2O3–SiO2–MgO silicate slag system with a CaO/SiO2 weight ratio of 0.65. Finger-test experiments with several corrosion steps were carried out in a contemporary continuous wear testing device at 1450, 1500, and 1550 °C with 200 rpm. The corroded sample profiles were measured using a high-resolution laser scanner, and the processed measurement data were used to extract the dissolution parameters (i.e. corroded volume, surface area, mean radius, tip radius and immersion length). The diffusivity determination method using Sherwood relations was developed for the dynamic finger-test setup. The diffusivities for all corrosion steps were determined from these dissolution parameters, and those obtained from the Sherwood relations were compared with the ones received by a simulation approach that includes deviations from the cylindrical shape. The results obtained using Sherwood relations are sufficiently accurate in several cases.