If a permanent marker is used on cardboard, the markings can be extremely difficult to remove. Because cardboard is porous, it absorbs the ink. While removing the ink, you must also be careful not to saturate the cardboard with liquid, as this can damage or distort the cardboard. Toothpaste and rubbing alcohol may help lighten or remove the stain. It may take several attempts, and there is no guarantee it will be removed. The sooner the stain is cleaned, the better chance of removal.
Dip a clean rag or cloth in acetone or acetone-based nail polish remover.
Dab at the permanent marker spot on the cardboard. Do not rub, as you can spread the ink.
Continue dabbing until the spot is lifted or the cardboard becomes wet. If the cardboard becomes overly wet, allow it to completely air-dry before continuing to dab.
Place a pea-sized amount of white toothpaste onto your fingertip.
Rub the paste into the cardboard. Allow the paste to dry on the permanent marking. This should take about 15 minutes.
Dampen a cloth or rag. Wring the cloth to remove moisture. Dab at the spot to remove the toothpaste and lighten the spot. Repeat the process until the spot is removed.