What is the writing principle of water-writing cloth?

In fact, the magical writing of water cloth is not magical. People have been enlightened in this respect for a long time: when it rains, when the rain permeates the whole wall, it is found that some invisible patterns on the wall are now looming. This is the original principle of water-writing cloth, but people don't care about its development and utilization. The water writing cloth we see now is developed according to this principle. On the other hand, the principle of this kind of water-writing cloth is really simple, but it has several advantages: 1. When people practice calligraphy, it is inevitable to spend a sum of money to buy paper and ink. As long as a pen is added, they can practice calligraphy with water book cloth. 2. Environmental protection and low carbon As we all know, the paper people use every day is made from a large number of trees. If people all over the country practice calligraphy with paper, our home will lose its green aura. For the sake of our green home, please use paper carefully, and calligraphy cloth is the best choice. It is sanitary and convenient to practice writing with ink. Of course, splashing ink is inevitable. Wash the child. Writing cloth is just different-clean and convenient. Finally, I still suggest that everyone should strengthen environmental awareness for our beautiful home: green travel, low-carbon life and low-carbon calligraphy.