Water contact causes chemical reactions (ion exchange between cations in the glass and hydronium ions in water) that result in a silica-rich surface layer that causes an interference color on that layer. When damage is caused to the polished optical glass surface by moisture and acid, the reflected light of an interference color may be seen on that surface.
The resistance of a glass to dimming is expressed in terms of 'water durability by the powdered method*(D W).'. Reaction products form as white spots or a cloudy film as the glass surface dries. Some of the glass components that dissolve in the droplets may in turn attack the glass surface and react with gaseous elements in the air (CO 2, for example).
Water vapor may condense to form droplets on the glass surface. Polished glass exposed to high humidity and rapid temperature variations may 'sweat.'. These surface defects are caused by chemical reactions of glass constituents with water in the surrounding environment or with detergents in the cleaning fluids. In the various processes of fabricating optical components such as lenses and prisms, surface deterioration is often encountered and recognized as dimming, staining and latent scratching. Top > Technical Information > Chemical Properties
