As the old saying goes, how to pay for calligraphy?

In ancient times, people used a brush to write, but before using the brush, they usually soaked the brush in water to make the hair of the brush open and soft, so that the brush could absorb ink more easily and feel more round when writing. Therefore, the action of soaking the brush in water is called "moistening the brush". Later, "run pen" generally refers to the remuneration for inviting people to write articles, writing and painting.