My elementary school(Our Lady of Mercy--Marion Avenue, Bronx NY) had greenboards-

i didn't know/think they were made from glass, but we did call them 'blackboards'--tho, occationally, 'chalkboards'was used(or did i learn that word later?)

2 of the 4 classroom walls were covered with them.

often, with the overcrouded classes, students had seats next to a chalkboard, and would write small notes on them.
teachers had freedom to make the wall at right angles to the windows, or opposite the windows 'the front' of the class. (opposite was often chosen on north facing classrooms)

i remember being surprized in HS, that classes there had fewer students, and blackboards only on one wall.


my other obsession