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 should not be less than 200mm, the width should not be less than 650mm and the height should be 200 mm.
Extended data:
Functional features:
The teaching blackboard is hard and non-reflective, and is used for teaching. The surface of teaching blackboard is generally made of magnetic color coated steel plate, and the thickness of the surface 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 generally made of wooden boards or frosted glass, and you can write on them with specific writing materials such as chalk. Mostly 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 walls painted with these murals can already be called blackboards in the traditional sense.
In ancient China, an object called sand table was often used in teaching, and hardwood was used to write on sand repeatedly. However, because of the softness of sand, it could not 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 pen. In the19th century, people painted the surface of wooden boards with black paint to protect them from erosion. Of course, the main function of blackboards at that time was not teaching, and it was not until the middle of19th century that they became popular in schools all over the world.