Wool is made from the hair or tail hair of green sheep or antelope. Textual research began before the Northern and Southern Dynasties. By the Qin Dynasty, Meng Tian's improved new pen had become a pen-making material. Calligraphy is the most important thing, sheep are soft and have no front, and books are "weak and boneless", which are rarely used by calligraphers in past dynasties. Sheep hair became popular only after the Southern Song Dynasty. But it was widely used after the early Qing Dynasty. Because the Qing Dynasty paid attention to roundness and delicacy and was not allowed to show off talents, only soft wool could meet the requirements and was widely used at that time. The softness of wool is also poor. If it is properly combined with paper and ink, it can also show a plump and gentle style, and it is cheap and easy to get. Wool is so long that it can be written in large letters more than half a foot.
Double two brushes have more than two kinds of pens, named according to their mixing ratio, such as three purple seven sheep and five purple five sheep. Meng Tian's improved pen, with deer hair as the column and wool as the quilt, belongs to a double-stranded brush. Double double brush takes one more health value and one more softness value to match, with health value as the main factor, which is called "column". Gentleness is a bad habit, called "righteousness". No matter how long the column is, the quilt is also short. This is called a pen with a column and a quilt. The quilt also has many layers, such as rabbit hair as a column, short wool quilt, and three layers of * * * are the same length as the column, so the root is extra thick, the pen tip is thin, and more ink is stored, which is convenient for writing. The characteristics are different according to the mixing ratio, either rigid or soft, or moderate in hardness, and cheap and labor-saving, all of which are advantages.