Free whiteboard from dried board marker
What really helped:
- Moist glasses cleaning cloths (this individually packed cloth with the cleaning agent in it).
What did NOT help:
- paint over with fresh board marker (did not work)
- Glass cleaner, soak with glass cleaner (helped in places)
- rub dry (has helped in places)
- wipe wet (no significant effect)
- (damp) microfiber cloth (helped a little)
The glasses cleaning cloths seem to be quite aggressive, so could possibly attack the board itself.
So first try everything else and consider the cloths as a last resort. My whiteboard does not seem to have hurt it yet.
