is a cloudy condition on the surface of glass bottles that can appear after a period of time, especially on re-usable bottles that have been run several times through a washer and filler. Bloom is a chemical reaction and part of the aging of glass. Technically, residual mobile ions, such as sodium ions, leach out of the silica sol and react with ambient moisture (SiONa + H2O → SiOH + NaOH). The newly formed sodium hydroxide, or lye, (NaOH) gradually dissolves the glossy outer layer of the glass and turns it hazy. This may take months, but will not occur in dry and relatively cool environments. There are various methods of removing bloom. Just washing a bottle with water can remove minor bloom, but severe bloom requires a soaking for about five minutes in HCL (at around pH 4) and a subsequent rinse. To retard bloom, many glass manufacturers apply a protective coating of sulfur, fluoride, or Freon compounds to their bottles.

See also scuffing.