Our green ones varied in quality and material. Most of them seemed to have some cheap coating that was sometimes torn by chalk; after being torn, the edges of g

Our green ones varied in quality and material. Most of them seemed to have some cheap coating that was sometimes torn by chalk; after being torn, the edges of green coating seemed stretched like thin plastic. Some of the green ones, the teachers actually liked. Maybe those were porcelain? Also had blackboards at some of my schools. They seem to last forever without much care.