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03 Aug 2016
chalk markers
Black board dates back towards the first organized school classroom. Probably, several Centuries ago. Before that, they used a charcoal stick and wrote on any flat work surface available. The situation being, charcoal doesn't erase, so a new writing surface was required very often. Before they needed chalkboards, somebody was required to invent chalk for that chalkboards.

liquid chalk
It had been discovered crushed up limestone produced a white powder that is compressed in a soft white stick that might produce a white line as opposed to the black line that the charcoal stick left. The best part was it erased off of an even stone surface. Then some bright fellow cut thin slabs of slate rock, polished it as well as the...