Patterns on the surface of the glass are dull or faded.
This is most noticeable when comparing with new glasses of the same type or with the undamaged pattern on the inside of the glass.
Usually the result of:
Very soft water
Poor quality glassware
Cause & Prevention
Fading of patterns is caused by the removal of metal ions from the coloured area and this is very often a result of very soft water.
Part of the detergent is designed to remove calcium ions from the water (builders) but if there are few ions present, such as is the case in soft water areas, then this can cause the metal ions to be removed from the coloured pattern.
Teh fading is irreversible and there is no treatment or any way to restore the pattern
Buy good quality "dishwasher safe" glasses.
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