For reasons that have never been clear to me, about 20% of the
white boards I come across have one or more permanent markers
mixed in with the dry erase markers that you're supposed to
use. Obviously, this is a trap, because once you've unwittingly
written something using a permanent marker it's pretty much
there for good. Thus my distress on Monday when I realized that
my diagram about porn downloading was going to be preserved forever.
Luckily, one of the people in the meeting with me showed me a cool trick: if you write over the permanent marker with a real dry erase marker you can often erase them both. Don't ask me why this works because I don't know, but it seems to. Just FYI.
But you really should preserve your diagram on porn downloading in the blog forever...
Often, water or whiteboard cleaner works as well. I think what is happening is that the solvent in the dry-erase pen is penetrating the "don't erase" ink underneeth, loostening it up. Useful trick, tho.
Most marker-boards tell you that you can erase permanent marker with typewriter cleaner.
On the other hand, nowadays you have to go to an antiques shop to find typewriter cleaner. But if you are really stuck, there's an antique typewriter shop in downtown Los Altos, just down the street from the Runner's High. They can probably help you out.
It's easier than that. The "permanent" marker does not penetrate the board, and it wet when it comes out of the pen. Go back over your lines with the "permanent" marker & immediately erase.
It's when the solvent evaporates (fairly quick) that the mark becomes "permanent".