A method for treating a plurality of indicator fields for determining the pH-value of an aqueous solution is provided. Each of the indicator fields contains at least one indicator dye, which is fixed in a non-bleeding manner, in particular on a layer including cellulose or regenerated cellulose, and changes its color within a pH-turning-range. The indicator fields having buffer capacities which differ from one another. All the indicator fields are impregnated from the outside with an impregnation which influences the buffer capacities of the indicator fields in such a way that the deviations are levelled.