fogging bath containing a water-soluble stannous salt and a phosphonocarboxylic acid compound and then color developing the light-sensitive material, the phosphonocarboxylic acid compound being represented by the general formula (I): ##STR1## wherein R.sub.1 is --COOM' or --PO(OM).sub.2 ;R.sub.2 is a hydrogen atom, an alkyl group containing 1 to 4 carbon atoms, --(CH.sub.2).sub.n COOM' or a phenyl