During hot corrosion in fossil-fuel-fired power plants a molten salt layer, around 1 mm thick, forms on leading superheater and reheater tubes, under fly ash, and dissolves some of the metal surface. Previous studies have not been made with molten layers this thin. A crucible was designed to take metal coupons and maintain, for up to 2000 h, molten sulphate at 650°C around the coupons to a depth of around 1 mm. The crucibles were fabricated from a machinable glass ceramic impervious to molten sulphates. The experimental set-up is described and includes, for the first time, the continuous monitoring of both SO2and SO3in the synthetic flue gas. An account of the commissioning trials is also given. Crucibles were removed at 200 h intervals and sectioned for subsequent analysis by electron microprobe analysis (EMPA), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and spectroscopic studies of the corrosion products within the 1 mm salt layer. Preliminary results from a 2000 h experimental run are given for the concentrations of the elements iron, chromium and nickel entering the thin molten sulphate layer from both oxidized and carburized samples of 304 and 310 stainless steel samples. It is concluded that the tests and evaluation were successful, and that this new crucible enables laboratory experiments to be made, which replicate closely the hot corrosion occurring on superheater and reheater tubes, and that the results accruing will reveal valid information on thin-film hot corrosion occurring in industrial power plants.