Some calligraphers who were also connoisseurs and collectors, including Mi Fu of the Song dynasty, believed that rubbings could not serve as a close approximation of the written word in its original form; carving tools and stone could never imitate the qualities of movement of the flexible brush, and the subtleties of ink density on the absorbent surface of paper or silk were simply not present in rubbing form.  At best, the rubbings were able to accurately transfer a sense of how the individual calligrapher composed characters on the page as well as the quality of the line structure in his writing.