I'll try that. We usually use spray bottles of Fantasik, Lysol and 409 to clean them so it may be something in them thats causing that.You can try daubing them with a weak solution of household bleach and water (diluted 10:1), then rinsing them after a couple of minutes. I've had good luck with that in the past.
You are coorect in theory as far as I can tell because it works the same with using permant marker on dry erase. One removes the other.If you used wet erase marker on them, carefully draw over the "ghosts" with DRY erase marker and then clean.
(Try on a small spot first! This unaccountably works sometimes, but not always!)
This is what I learned to do as a teacher on whiteboards, too.
I had a friend who worked at a sponge factory and used to bring me boxes of Mr Clean Magic erasers. As I said Im going to try the suggestions but I think these lines are now one with the mats. Hopefully I get lucky.A Mr Clean Magic Eraser will also take off "ghost" lines from a Chessex map.
Unfortunately it will also take off the ACTUAL lines on the map. So again, try a small spot first.
At least it was just a river. One of my players likes to absent-mindedly doodle on the battlemat while we are playing, and he drew...well, suffice to say, it was a very well-endowed river.Might try some of this.
Years ago, someone accidentally drew a river on one of my Chessex mats using permanent markers. Oops.