Sigel Chalk Marker, Round Tip 1-2 mm, 2/pack, Blackeasy to wipe off for glass and all smooth surfaces similar to glass Sigel GL177 thin round tip 1 2 mm liquid chalk with excellent covering power fast dry 2 pack Black The two black chalk markers 20 with the 1 2 mm rounded nib write with opaque liquid chalk and are suitable for use on smooth glass and sealed surfaces. The water based chalk can be wiped off with a damp or dry cloth.