Condensation

When condensation forms on a glass surface, the rate of formation and appearance of the condensation can vary across the surface if there are contaminant present on the glass surface. The variation may be random, but can show up as distinctive patterns. The most common contamination is from finger marks, but any contamination which creates a hydrophobic surface layer - grease and some other organic materials - will produce these effects.

The surface contamination which causes these effects results from a very thin layer of material, usually transparent, and in dry conditions it may not be detectable. The windows may appear to be scrupulously clean, but show marks when condensation is present.

The surface contamination can often be removed by cleaning the glass with an ordinary window cleaner or a degreasing agent, but some surface contamination can be of a more obstinate nature. For example, deposits form glass-carrying suckers can form chemical links to the glass surface, making them very difficult to remove, except with a mild abrasive followed by re-polishing of the glass surface.

These variations in appearance under condensation conditions do not indicate any fault in the glass. The surface contamination has no effect on any mechanical or physical property of the glass, other than its appearance.

It should be pointed out to anyone who has condensation on the room surface of double glazing units that the presence of the condensation is an indication that conditions in the room may be deleterious to other items and that they should consider improving the ventilation to the room.