the.com/chalkboard
A wall that remembers your math until someone smears their sleeve across it.
means A smooth dark surface you write on with chalk and erase with a felt brush or rag.
from From chalk (Latin calx, lime, the same root as calcium) plus board; the surfaces were originally just plain black, hence blackboard, the older name.
Not always blackGreen became popular for less eye strain mid-century.
Real chalk isn'tSchool chalk is usually gypsum, not calcium-rich rock chalk.
That screechNails on slate hit a frequency primates instinctively dread.