What pen did he use?

I remember that he and Deng Dou used the wool of the long peak sheep. Look at his official script, it's quite clear. The early years are also the foundation of terns, but the mature style is obvious and the basic changes are not big. He is also good at small letters and doesn't know what brand of pen to use.

In order to increase trust, I found some materials to prove:

. . . When he wrote How to Write a Calligraphy, he used only one writing tool, but he could write several similar faces. What is common in later generations is calligraphy in the posture of "hanging back to the wrist". When he writes this word, his wrist must be flat, and the lines he writes are full, smooth and slightly trembling. What is commendable is that his pen is round and powerful. His ink is thick and light, and the ink on the paper is extremely full. The whole calligraphy works are rare, and in some places only the word "Shang" can be seen; The ink color and charm of his works transcend the limitations of calligraphy and are full of painting meaning, and ink is its victory. Its structure not only has the characteristics of Yan Zhenqing structure, but also combines the meaning of Li (book) and the taste of Wei (monument). The thickness of the pen line varies greatly, and there is a meaning of "spring silkworm spinning silk" between the pen and the word. Most of the rules are full and plump, and the boundaries between lines are not obvious because of the wrong size of words.