I remember practicing my calligraphy on "water-writing paper" (with @pixljar and other friends) as a youngster. I found a few sheets lying around and got curious. The comments here https://www.reddit.com/r/chemistry/comments/pcf6g/how_does_magic_paper_work/ … suggest that some "magic paper" is made of multiple layers: 1/6https://twitter.com/telemooon/status/1167752568778280960 …
I then found a Baidu article https://baike.baidu.com/item/%E6%B0%B4%E5%86%99%E7%BA%B8/5932571 … (google translation shown) explaining that there are indeed two types: those based on a "physical change" (fitting the Reddit description) and those based on "chemical reactions" (the ones I have seem to be of that type). 4/6pic.twitter.com/FLMjhzxnnx
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I then dug up two patents with more details. So far as I can tell via the machine-translation and my poor Chinese, the first https://patents.google.com/patent/CN85101953B/en … from 1985 is related to the "physical change" type and covers the use of activated clay (aka fuller's earth) for the top layer. 5/6
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The second patent https://patents.google.com/patent/CN1048572A/en … from 1990 is related to the "chemical reaction" type and describes a coating made of a slurry containing carbon black, water, polyvinyl alcohol, kaolin clay and some other stuff. I sort of get it, but I'm still curious to learn more! 6/6
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As an aside, figuring out that "higher Ling soil" = kaolin clay was tricky: the patent reads 高砱土 but it should be 高岭土, after 高岭村 (Gaoling village, see https://en.wikipedia.org/wiki/Kaolinite ). A related oddity: in this screenshot from the scan, you can see 砱 written in by hand! 7/6pic.twitter.com/AkEcooWaL1
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