Preface to Lanting is definitely not written on rice paper!
Wang Xizhi's Eastern Jin Dynasty had paper, but there was no rice paper at all. Even in the Tang dynasty, there was no rice paper. A discerning teacher can see that the imitation of Longlanting in Tang Dynasty is not rice paper. At that time, it was widely rumored that Koreans boasted that Lanting was written in Korean paper, which was ridiculous, because the papermaking technology at that time had been lost, including the pen-making technology of the Wangs at that time.
Xuan paper is not an excellent writing paper, especially for health preservation. Excellent calligraphy and writing paper needs to eat ink and is not cured, and its health is not good. Before the Ming dynasty, the original paper of the ancients was also matured, but the writing paper at that time had post-processing technology, mainly adding plant juice, drying and then hammering to suppress light.