In addition, the surface of the blackboard should be made of wear-resistant and dull materials. The horizontal distance between the two ends of the platform and the edge of the blackboard is not less than 200 mm, the width is not less than 650mm, and the height is 200mm.
Extended data:
Functional features:
The teaching blackboard is hard and non-reflective, and is used for teaching. Generally, the surface of teaching blackboard is made of magnetic color coated steel plate, and the surface thickness is mostly between 0.2 mm and 0.4 mm. This material has the characteristics of wear resistance, no falling off, no fading, durability, good writing feel, clear handwriting and easy writing and erasing.
Blackboards are usually made of wooden boards or frosted glass, and you can write on them with specific writing materials such as chalk. Most of them are black, dark green, white or beige.
Before the invention of writing, people found that charcoal can be used for painting, and some ancient murals can be found in some ancient caves in Europe. The rock wall painted with these murals can already be called a blackboard in the traditional sense.
In ancient China, an object called sand table was often used in teaching, and hardwood was used to write on the sand repeatedly. However, due to the softness of sand, it cannot be regarded as a blackboard.
In the Middle Ages, people found that lime was mixed with water to make a block, and they wrote on the surface of dark and hard objects in a way similar to charcoal pens. In the19th century, people painted wooden boards with black paint to protect them from erosion. Of course, the main function of blackboard was not teaching at that time, and it didn't become popular in schools all over the world until the middle of19th century.