While the term may suggest it, glass corrosion is not the reaction of glass with oxygen - but a reaction of glass with humidity, water and chemicals. In foodservice, it occurs when washing glasses. The exchange of ions changes the chemical resistance of the glass. The result: Every time a glass is washed, a tiny amount of the glass material is removed from its surface.
On a new glass with a smooth and even surface, this removal is even and visually undetectable. However, if the glass is older and has already been damaged, more glass will be removed in some spots than others. This changes the way light is refracted and the uneven removal becomes visible: as milky clouding (cloud corrosion) or in the form of fine white lines (linear corrosion).
And what about rainbow-coloured shimmering? This is also a consequence of the removal of glass material. This is because the silicate structure of the glass is also dissolved in the process – and the silicates are deposited as layers on the surface of the glass and then shimmer in rainbow colours. This process is callediridescence.