I just read this on the newsletter from Quilted Paradise that handles this board. I've not tried it, but it gives you another option.
"What can you do when your quilting pencil marks do not come out? I've even tried a different pencil. Kathy
Subscriber comments:
To remove pencilled quilting marks, try the following: 6 T. alcohol, 2 T. water, 2 drops liquid soap. Use an old toothbrush.
Marilyn"