because you have to let it dry
Some of the chalk is dissolved into the water and so when you write on a board the chalk can not easily be seen. The water then evaporates leaving only chalk behind therefore becoming visible.
Use a wet towel or sponge. put a few drops of detergent in the water. After the (slate0 board is dry, chalk it by rubbing the side of a stick of chalk all over it then erase it with a felt eraser.
Blackboard manufacturers often advise that a new or newly resurfaced chalkboard be completely covered using the side of a stick of chalk and then that chalk brushed off as normal to prepare it for use. Blackboards are commonly used in teaching. The chalk marks can be quickly and easily wiped off with a damp cloth or a special blackboard eraser consisting of a block of wood covered by a felt pad. Chalkmarks made on some types of wet blackboard can be difficult to remove.
A towel
A towel
It is not recommended to apply hair chalk on wet hair as it may not adhere well or provide the desired color payoff. It is best to apply hair chalk on dry hair for better results.
chalk has a compound in it that releases the glow when wet.
It dries out...
They don't lol
Mud cracks form when wet mud dries. As mud dries, it shrinks and cracks start to form.
because the particles of the chalk or any other substance which is used to write on black board has very tiny particles which get attached with white board.