fivej.net - In this video demonstration Jacob shows that with some elbow grease and a certain sponge, their chalk marker ink comes out of porous surfaces. It is of course not recommended to write of porous surfaces with the chalk markers but if it happens it can come out.These chalk pens can be used on windows,mirrors, blackboards, some chalkboards and a specialized chalkboard paint for chalkboard painted walls we illustrated in a previous video. These markers are used at pubs, restaurants, clubs, hotels, restaurants, cafes and all other places with menu boards, led writing boards etc.