Most chalkboards are made from enamel and steel. The enamel used to make a chalkboard is made from a porcelain base, which is applied onto large steel plates. The writing surface for vintage chalkboards is made from slate rock or grit paint applied to wood.
From the 1800s, and well into the 20th century, chalkboards were primarily made from large pieces of slate rock that served as the front of the board. These larger boards were an improvement over individual slates used by students. Slate rock for chalkboards was shipped around the country via railroad, and it greatly improved the effectiveness of a classroom teacher's ability to share information with a large number of students.
Slate boards were referred to as blackboards during the time they were in use, due to their dark coloring. It wasn't until the 1980s that the name "chalkboard" became popular, which is when boards largely switched from black to green.
Enamel chalkboards quickly became the norm in many school rooms. Their green coloring is considered easier on the eyes than the stark black. In addition, enamel chalkboards are cheaper to manufacturer and are sturdier than slate boards. Traditional chalkboards are rarely used in modern classrooms as of 2014. The dust from chalk poses a health risk to some students and can damage computer equipment.