A brush dipped in water can write black words on a piece of paper. When the water is dry, the characters are gone. What kind of paper is this? What's the principle? Answer both.

It's called writing paper. I used it. This paper is coated with a special paint that changes color when it meets water. When writing on paper with a brush dipped in water, the paper will show obvious marks different from other parts, and then return to its original color after drying. It can be used for copying copybooks or other similar occasions and can be reused.

Shuishu paper is a kind of writing supplies, which plays the role of paper. Characterized in that one side of the transparent plastic paper is frosted, and the other side is made into a colored surface or a colored pad. Writing on it with water instead of ink can show handwriting, and the water can be reused after evaporation.