Blackboard

A blackboard or a chalkboard is a reusable surface where people can write or draw using sticks of chalk. These sticks are made from materials called calcium sulphate or calcium carbonate.

Originally, blackboards were made from smooth, thin sheets of dark stone called slate. They provided a dark background that made the white chalk stand out clearly, making it easy for everyone in the room to see what was written.

Blackboards have been an important tool for teachers and students for many years, helping share ideas and lessons in classrooms all over the world. Today, many schools use different kinds of boards, but the classic blackboard still reminds us of the history of learning.

Design

A blackboard can be a simple board painted with dark, non-shiny paint, often black or sometimes dark green. Some blackboards are made from a special plastic material that looks like chalkboard and can be shaped into art pieces. Restaurants and bars sometimes use blackboards on A-frames to show their daily specials. There is also adhesive blackboard material that can be stuck to walls or doors.

Modern blackboards can have a rolling sheet of plastic that moves between two rollers, giving more space to write and saving what was written before. The best blackboards are made from a very strong type of painted steel and can last many years of heavy use. Big lecture halls often have several blackboards arranged in a grid, so lecturers can easily move them to write and show lots of information at once.

Chalk sticks

Chalk sticks come in white and many colors, especially for use with blackboards. White chalk sticks are made mostly from a mineral called chalk or limestone, which is calcium carbonate. Colored chalk sticks are made from calcium sulphate in a special form called dihydrate, written as CaSO₄·2H₂O, which comes from a material called gypsum. Chalk sticks that contain calcium carbonate usually have about 40–60% of CaCO₃ (calcite).

Issues with use

When people run their fingernails or sharp metal objects across a blackboard, it makes a very unpleasant sound that most people dislike. Research from the University of Cologne in Germany showed that humans naturally hate this sound. These findings were shared at a meeting of the Acoustical Society of America and agree with older research from 1986.

Some studies have found that chalk dust can affect the breathing of school teachers and others who spend a lot of time near blackboards. The tiny particles from chalk can sometimes cause problems for respiratory health.

Etymology and history

In old Indian schools, children used black tablets for writing, as described in a book from the 11th century. Large blackboards began appearing in European schools for music lessons as early as the 1500s. The word "blackboard" was first used in English in the 1700s. In the United States, chalk was first used on a blackboard in 1801 during a math lecture. By the 1840s, factories started making blackboards from slate. In 1930, green enamel boards were introduced, and they became common in schools in the United States during the 1950s.