The very first chalkboards were constructed from slate, either black or a deep gray. Contemporary chalkboards come in additional colors such as green or brown. The finest level of chalkboard is constructed of steel sealed over with porcelain. Since porcelain is so durable, these chalkboards can last for decades even if they are used continually.
Chalk is the writing tool used on these boards and it gives them their name. It is generally white but can be produced in other colors as well. The chalk is actually a chemical named calcium sulfate. This chemical is refined from its original mineral state to produce chalk. Before it is processed it is a rock of a white color. After the chalk marks up the board, the results can be removed with a wet piece of material or erasers produced specifically for use on a chalkboard. These are basically small pieces of wood covered with padding.
The predominant use of the chalkboard is to enable teachers to reach a large number of students by using it as a canvas to convey ideas. Some public businesses such as bars and restaurants use blackboards as well to record notable dates at the establishment. They might also use it for listing items they will be serving. People occasionally have small chalkboards in the home, very often in the kitchen, for making note of things for family members to remember.
The word chalkboard has been in use since the mid 1930s but the item itself was actually part of education in America since 1801, when they found their way into military schools. The first one was used at the U.S. Military Academy at West Point in New York. A teacher there named George Baron discovered their use would enable him to teach a much larger number of students. Until this time, pupils would each have to carry their own smaller chalkboards around. For teachers, this created an undue workload as they needed to continually rewrite problems and lessons for each student. This also forced class sizes to remain small. Once the use of the larger boards was realized, they found their way into communities all over the nation, through shipments enabled by the booming railroad industry.