Traditional alternative to 水寫布 (water-writing paper) for calligraphy practice?
Don't know if it counts, but in mainland China, some people write on the street with a huge writing brush, half as long as an adult is tall. And they only dip the brush in water to write. After the water evaporates, the writing vanishes. It's the same principle as 水写布



Beijing - Public calligraphy by Roman Harak licensed according to CC BY-SA 2.0