The corrosion layers of a glass object may be deemed a part of the history of the object, and thus a diagnostic attribute, and should not be removed without good reason. It occurs naturally on flint and obsidian and is the basis for obsidian hydration dating. The surface of any glass from any time period, especially soda glass, usually becomes hydrated through time and so will eventually devitrify. Devitrification occurs when the surface of the glass becomes partly crystalline as it adsorbs moisture from the atmosphere or from a submerged environment. As it becomes crystalline, the surface becomes crazed and flakes from the body of the glass.
Devitrified glass has a frosty or cloudy, iridescent appearance.
Pane glass is especially susceptible. To prevent further devitrification and to consolidate the crazed surfaces, a coating of PVA or Acryloid B-72 should be applied to the piece. Either of these surface adhesives will smooth out the irregularities in the pitted, crazed surface of the glass by filling in the small cracks and forming optical bridges, making the glass appear more transparent. Merely wetting glass will cause it to be appear clearer for the same reason. A 10-15 percent hydrogen peroxide solution is used, as with ceramics, to remove these sulfide stains.