The relationship between impurities of silver behenate and their synthetic conditions is investigated to produce the thermally processed silver (TPS) film on an industrial scale under the well controlled manufacturing conditions. Fogging (OD_min) increases as pH of sodium behenate solution shifts to a high alkaline side, in spite of no detective difference of the final products (silver behenate) by chemical analysis. This suggests the possibility that Ag₂O in the salt and/or reducing catalytic substances from its Ag₂O cause fogging from the TPS film. On the other hand, although chemical composition of the salt is widely changed in an acidic region by more excess HNO₃, it hardly affects any initial photographic characteristics.