Shufa 書筏 "The raft of calligraphy" is a sister-work of Huaquan 畫筌, a book on painting. Both were written by Da Chongguan 笪重光 (1623-1692).
The transmitted text of the Shufa has a length of 28 chapters. It discusses important aspects of calligraphy, such as brushwork, the right use of ink, layout and style. It is and important and concise text which reflects the author's profound skills in the art of writing. Da says that many people only knew to start with the brush and "hide the sharp edges" of characters (qi bi cang feng 起筆藏鋒), and were not aware of the difficulty to "retain the brush and bring out the sharp edges of brush strokes" (shou bi chu feng 收筆出鋒). Only with a thorough knowledge in the use of the bafen 八分 style and of the separated-characters grass script (zhangcao 章草), this skill could be mastered. The method of using the brush was lying the the observance of rules, and not in the hardness or softness of wrist and hand.
The Shufa was originally perhaps circulating along with the Huaquan, but the latter is written in very elegant verses, while the language of the Shufa is prosaic and not well polished. Some authors therefore believe that the text of the Shufa is not complete, or was corrupted in the transmission process.