A graphical experimental approach, which makes efficient use of experimental data, has been developed for optimising conflicting interactions in a sequential two-stage process. The results are presented in the form of feasibility graphs, which provide valuable process design information, including a quantitative measure of the 'robustness' of the proposed process. This method has been developed here for selecting and optimising additives for sintering reaction bonded O-sialon ceramics, but has wider-ranging potential applications.