Counter-current continuous ion-exchange method for strengthening glass articles

A method of ion exchanging at least one glass article, the method comprising:

• providing a glass article containing metal ions that are exchangeable with larger metal ions,
• disposing the at least one glass article in a cassette;
• providing a vessel containing molten salt having an ion exchangeable with at least one ion in the glass article, the vessel having an outlet end for removing molten salt from the vessel and an inlet end for supplying a fresh molten salt to the vessel, the inlet end being distal to the outlet end;
• providing an element for placing the cassette contain the at least one glass article into the molten salt bath at the vessels outlet end and translating the cassette from the vessel's salt outlet end to the vessel's salt inlet end to thereby ion-exchange metal ions in the glass with larger metal ions in the molten salt bath;
• wherein:
• the molten salt comprises a first salt having a first concentration and a second salt having a second concentration, wherein the first concentration and second concentration vary form the inlet end to the outlet end, and the concentration of the first salt at the vessel inlet end is substantially 100%;
• and
• the first salt metal ions are larger than the second salt metal ions are ion-exchanged into the glass to relace the second salt metal ions;
• and
• the at least one glass article is ion-exchanged to a selected depth of layer while being disposed in the ion-exchange vessel.