Anti-dust Blackboard Chalk. Writing on the blackboard without chalk dust or chalk fingers. This is possible with this almost completely dust-free, hard blackboard chalk that comes in 9 colours. This chalk can also leave a residue on certain blackboard surfaces. Cardboard box, 12 crayons, white, diam. Approx. 9.5 mm, length: approx. 80 mm (diam. Approx. 0.37 inch, length: approx. 3.15 inch).