Wet Erase Chalk Marker White MediumThe Pentel Wet Erase Chalk Markers can be used either indoors or outdoors. They\'re great for using on menu chalk boards! The semi-permanent formula prevents it from running off during light rain once the ink has dried. It can however be removed with a damp cloth. You can achieve different thickness lines with the chisel-style tip. (approx 1. 5-4mm). Ideal for use on black boards, slate boards and glass. Unsuitable for use on MDF, painted on wood or vinyl boards.