Blackboard

Blackboard

NASA scientist Homer E. Newell Jr. explaining principles of altitude, pressure, and temperature, c. 1973
Other names	Chalkboard, writing-board
Uses	Reusable writing surface on which text or drawings are made

A blackboard or a chalkboard is a reusable writing surface on which text or drawings are made with sticks of calcium sulphate or calcium carbonate, known, when used for this purpose, as chalk. Blackboards were originally made of smooth, thin sheets of black or dark grey slate stone.