The pO2 of the tin melt and atmosphere in industrial tin baths for the production of float glass is continuously measured using oxygen sensors from the hot end to cold end. Under normal production conditions, the pO2 of the atmosphere is determined by the water dissociation equilibrium. The measured partial oxygen pressures of the tin melt are higher than those of the atmosphere in a particular bay, indicating that the oxygen from the glass ribbon is entrapped in the tin melt underneath it. The oxygen level in the tin decreases on moving from the hot end to the cold end. A relation is derived to quantify the oxidising or reducing effect of the atmosphere on the tin melt. It shows that the driving force for tin deoxidation is smallest in the hot end. Therefore, the water vapour content in the hot end atmosphere should be kept low. This can be achieved by intense venting and good sidewall sealing in the hot end section. Back flow of the relatively water rich atmosphere from cold end to hot end should be prevented and a reduced tin temperature in the hot end also helps to keep the oxygen level of the tin melt low.
