The earliest discovered, charcoal can bring painting, far before the invention of writing, the human use charcoal to paint a picture, in Europe in the cave can still see carbon powder, or charcoal do stone walls. During the middle ages, people began to find that with lime water, can make it massive objects, can use similar charcoal pen method, to record in the dark, or a hard surface. (the s paper is very expensive items, engraved on the board on the rock with carbon pen and easy fuzzy).

Of course after nearly one thousand years of time in the past, now has been difficult to textual research exactly is who first thought of the idea, but the earliest, chalk effect, absolutely not bring with teaching. To widely applied to teaching, the importance of the more important than chalk.

In the 19th century ago that with black paint besmear is on board, and is in order to protect the board from erosion. Also and released for important events, more like now the role of the bulletin boards. But at that time "blackboard" are small, and the purpose is not used for teaching. But in the middle of the 19th century, the universities began to flourish, the original teacher oral, students mouth remember teaching way, because the number of students increased more and more revealed his inconvenience, so in Europe, in the United States began to common originally small, not fixed black bulletin board increase, used to teaching with convenient distance students copy teacher's dictation.
Chalk - clean chalk
Clean chalk belong to common chalk improvement products, designed to destroy the classroom chalk dust pollution. It is only in ordinary chalk to add fat class or polyalcohols material as bonding agent, and add the proportion of large packing, such as clay, marl, cement such as can make chalk dust weight and volume are increased, not easy off, but in practical application, it to chalk dust pollution reduction effects is not very obvious.

Clean the main advantages of chalk

(1) adding a small amount of smooth agent and binder, chalk don't touch with one's hand and clothes, the teacher after a lesson fingers without white mark, do not need to wash their hands.

(2) the main ingredient in adding trace chemical raw materials, increase the specific gravity, chalk to write on the blackboard, clean fly phenomenon, clean, to avoid the for chalk foam through breath into the visceral and occupational disease.

(3) to add a little moistureproof agent, long time storage not metamorphism. Ordinary chalk long time storage extremely easy absorption of moisture, hardness drop, write break easily.

(4) clean chalk in addition to production white outside, still can produce bright red, yellow, green, blue, pink and so on the many kinds of colour, and long term storage, chrominance won't drop, always protect thunder-and-lightning, color clear.

(5) the university now use the blackboard have floor slab, board and wool glass plate, etc., for the blackboard surface smooth degree, request the chalk level is not the same. I have a new generation of clean chalk can be arbitrary change its hardness, in all kinds of the blackboard use won't appear skid or dry phenomenon, and fluent in written, energy, and feel very good.
Chalk - chemistry and chalk
This is by the calcium sulfate hydrate (commonly known as plaster stone) is made. Also can join all kinds of pigment made color chalk. In the production process the plaster stone heated to a certain temperature, make its part of the dehydration into plaster of Paris, and then will be hot plaster water mixing into paste, penetration model set and become. The main reaction for:

2 caso4 · 2 h2o2caso4 · H2O + 3 H2O

Well control of temperature, the use of birth, plaster of Paris's interconvert properties can also make the model, statue and medical plaster bandage, etc.