It was found that the variation in zeta -potential with dilution for different formulations of a suspension of a commercial yellow pigment stabilized by means of block copolymers was smaller for the formulation exhibiting longer-term stability. Measures of the zeta -potential of various dilutions of a sample can be performed within a day, allowing faster identification of formulations with better stability than temperature cycle tests. A zeta -potential variation factor can be defined and may be used as a quantitative stability parameter for experimental designs. A limit in the applicability of the test is the minimum dilution required for reliable signal in the analyzer (based on light scattering and affected by opacity of the sample). The principle of the technique is based on the fact that the concentration of copolymer complexes affects its dispersing properties, and therefore the dilution shows which formulation is the more stable.