Iridescence is the rainbow effect seen on glasses when they are held up to light. The various colours may be mainly brown, blue or cover a range of the spectrum.
Usually the result of:
Detergent with a high level of disilicate
Very soft water
Long cycles at high temperature
Cause & Prevention
Iridescence is due to a slight unevenness of the glass surface. This causes different wavelengths of light to be reflected in different directions giving a rainbow effect.
The unevenness is usually caused by either slight attack of the glass surface by detergent solutions or by deposition of silica (glass) from detergent solutions with a high disilicate content.
Long wash cycles at high temperature increase the risk of iridescence.
Iridescence is permanent and there is no way to restore the glass to it's original condition.
Ensure that the water is not too soft. Check with your local water authority that the water is suitable.
Do not add salt to the machine if the tap water is
When possible wash glasses in low temperature, quick washes.
Use a quality detergent which is low in disilicate, such as Fairy Active Burst.