I like images of US based photographer Matthew Gamber who made this beautiful and simpel series of pictures of chalcboards. As an almost forgotten medium I think it deserves some more attention.

— …Currently, projectors and interactive LCD displays enable presenters to integrate graphics rendered more clearly than the unintelligible, temporary schematics drawn on these boards to emphasize abstract ideas. What is most alluring is not the layered decades of chalk residue, but the partial obscurity of what is written on the board – once public, now secretive. —