Crusty Staining on Double Glazing

[lancs_lad]

The window frames in the bedroom have developed a browny staining to them. It doesn't wipe off but I can scratch it off with my fingernails.

Any idea what it is and is there anything that will get rid of it because scraping it will take ages and be a pita.

Thanks

 

[Wayners]

Glue residue that's aged and gone brown.
Parcel tape does that along with other glues.

Use cif and soft sponge.
Don't use a scourer.
If that don't work DIY shop and solvent uPVC cleaner