A method of treating a substrate in a pressure vessel that includes the steps: preparing an ion-exchange bath with a bath composition that comprises a polar solvent and a plurality of ion-exchanging ions in a vessel; submersing a substrate having an outer region containing a plurality of exchangeable ions in the bath; pressurizing the bath in the vessel to a predetermined pressure substantially above ambient pressure; heating the bath in the vessel to a predetermined temperature; and treating the substrate for a predetermined ion-exchange duration at the predetermined pressure and temperature such that a portion of the plurality of exchangeable ions is exchanged with a portion of the ion-exchanging ions. The substrate can consist essentially of a glass, glass-ceramic or ceramic substrate composition, and the predetermined ion-exchange duration, temperature and pressure can each be selected based at least in part on the substrate composition and the bath composition.