A method has been formulated and tested in a laboratory device to evaluate the detersive and dispersant performance, as well as the washing dynamics, of surfactants and builders and the formulation of the detergent. The method, called bath−substrate flow (BSF), is based on the separation of the washing bath from the substrate to be washed after contact of the two by a cyclic-flow process. The method serves to analyze mechanical washing systems, such as dishwashers, tunnel washes, floor-washing machines, and industrial-scale cleaning systems. The circumscribed central compound experimental design was applied, as was the response surface method, to correlate the detergency values found.