Chalk is a widely used tool in daily life, which is generally used to write on the blackboard. Ancient chalk was usually made of natural chalk, but now it has been replaced by other substances.
The main component of chalk is calcium sulfate, which is a white precipitate, not easy to decompose, and its particles are larger than dust. There are two kinds 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.
Development history:
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.