Definition of chalk

There are two main types of chalk used in China: ordinary chalk and dust-free chalk. Their main components are calcium carbonate (limestone) and calcium sulfate (gypsum), or contain a small amount of calcium oxide. Chalk is a widely used tool in daily life, which is generally used to write on the blackboard. The main component of chalk is calcium sulfate, which is a white precipitate, not easy to decompose, and its particles are larger than dust.

The earliest humans discovered that charcoal can be used for painting. Long before the invention of writing, people painted with charcoal, and we can still see charcoal powder or murals made of charcoal in caves in Europe.

In the Middle Ages, people began to find that with lime and water, huge objects could be made and recorded on dark or hard surfaces in a way similar to charcoal pens. At that time, paper was a very expensive item, and it was easy to blur the lettering on wood and rocks with a carbon pen.

It is difficult to prove who first thought of this idea, but at the earliest, the role of chalk was definitely not used for teaching. To be widely used in teaching, blackboard is more important than chalk.

Before the19th century, black pigments were coated on wooden boards to protect them from corrosion. It is also used to announce important matters and compare the functions of similar bulletin boards. But at that time, the "blackboard" was very small, and its purpose was not for teaching. But by the middle of19th century, universities all over the world began to flourish. The original teaching method of teacher dictation and student dictation has become more and more inconvenient because of the increase in the number of students. Therefore, in European and American countries, the original small, unfixed black bulletin board is usually enlarged for teaching purposes, which is convenient for distant students to copy the teacher's dictation.

Therefore, the slow evolution in the past two hundred years has finally enabled more students to learn enough knowledge and eliminated the illiterate and ignorant masses through convenient tools. There are two kinds of chalk used in China: ordinary chalk and dust-free chalk.

Dust-free chalk is an improved product of ordinary chalk, aiming at eliminating chalk dust pollution in classrooms. It just adds grease or polyol as binder to ordinary chalk, and then adds fillers with higher specific gravity, such as clay, putty, cement and so on. It can increase the specific gravity and volume of chalk dust and make it difficult to fly away, but in practical application, its effect of reducing chalk dust pollution is not very obvious.

A small amount of chemical raw materials was added to the main ingredients, which increased the proportion. Chalk is written on the blackboard, which is dust-free and clean, to prevent chalk foam from entering the internal organs through breathing and causing occupational diseases.

Add a small amount of smoothing agent and adhesive, chalk will not touch hands and clothes, and there will be no white marks on the teacher's fingers after a class, so there is no need to wash hands.

Adding a small amount of moisture-proof agent will not deteriorate after long-term storage. Ordinary chalk is easy to absorb moisture when stored for a long time, and its hardness decreases, so writing is easy to break.

Blackboards used in schools include cement boards, wooden boards and frosted glass boards. Due to the different smoothness of the blackboard surface, the hardness of chalk is also different. The new generation of dust-free chalk can change its hardness at will, and it will not slide or break easily when used on various blackboards, and it is smooth and labor-saving, and has a good feel.

Dust-free chalk is a newly developed high-tech product besides cosmetic materials for production. Environmental protection, non-toxic, dust-free, is the ideal teaching office supplies for modern teaching.