Chalkboards

Chalk board blackboards go back to the first organized school classroom. Probably, several 100's of years ago. Before that, they used a charcoal stick and wrote on any flat surface available. The problem being, charcoal doesn't erase, so a new writing surface was required very often. Before they needed Chalkboards, somebody had to invent chalk for the chalk boards. It was discovered crushed up limestone produced a white powder that could be compressed into a soft white stick that would make a white line as opposed to the black line that a charcoal stick left. The best part was that it erased off of a smooth stone surface. Then some bright fellow cut thin slabs of slate rock, polished it and the chalkboard was born.