Pilot FriXion Ball Knock Gel Ink Pen - 0.5 mm - Black
Erasable Frixion Ball Knock Gel Ink Pen - 0.5 mm
Frixion Pens use a special thermosensitive ink that can be erased by rubbing with the pen's special rubber eraser.
The ink will also dissapear if exposed to other sources of heat.
Like magic ink, Frixion ink reappears if placed in a freezer.