I have recently been made aware of three patents having to do with the lithium salts or lithium vapor treatment for strengthening. All of these apparently have to do with the change in coefficient of thermal expansion. In two of these patents, formation of low thermal expansion crystals on the surface is described while in the third one lithium vapor treatment results in lithium either being dissolved or exchanged into the surface, thereby producing a lower expansion surface layer.. These patents are listed below:

1. Dec 11, 1971. Anchor Hocking, Shonebarger, #3,615,319, Li enriched ‘shell’ is in compression.

2. Feb 23, 1988. Corning, Pierson, Stookey, #4,726,981, Li, xtln.

3. March 21, 1989. Corning, Beall, Pierson, Stookey, #4,814,297, Li xtln.