a small army of janitors

I once taught at an old university where blackboards were still in use.  Hundreds of chalk drawings appeared and disappeared hourly.  It was a pity to see them erased.  I tried to photograph them between classes, before a small army of janitors got to them.  The  drawings described complicated concepts in matter-of-fact ways, without aesthetic pretensions or self-conscious effort.  They retained the trace of the hands that drew them, their spontaneous movements, their hesitations, mistakes, erasures and discoveries.  In the ephemeral hues of chalky gray I found small and interesting microcosms.