First, you should be sure that there is not a deposit on the glass. To confirm a water soluble film, run water over the spotted area and blot dry with a paper towel. Examine the spot to see if the residue has been removed. Removal indicates water soluble deposits.
To confirm a hardness deposit, determine if the film can be scratched off with a knife or similar object.
If it is not a deposit, it is probably a type of etching. There are two different causes for what appears to be etching on glassware:
Silica film in the early stages, glassware develops an amber to multicolored film, similar to an oil-on-water film. Lines of white or different colors commonly break the film’s uniformity. These lines follow deformities or stress lines in the glass.
As the process continues, the glass-ware develops patches of clouded glass (etch). Neither the films or the etch will respond to acid or bleach. Scratching with a pin or knife will remove the colored phase but not the white or etched areas.
A second but similar problem is etching whereby some of the material is removed from the glass.
First, try to confirm the etching. The glassware will appear cloudy; this can be a uniform haze or blotchy, as in the last stages of a silica film problem.
Again, scratching or treatment with water, acid or bleach will not remove the apparent film.
Remember, these detergents must be aggressive to work with very hard water.