Chinese researchers have developed two methods that make printed information invisible for the naked eye, and allow reusing the same paper several times. For their technique, they used a simple currently used jet printer, but replaced ink with water. In their study published in the journal Matter, the researchers led by Qiang Zhao of the Nanjing University of Posts and Telecommunications, said the water-jet printing method is environmentally safe. {"preview_thumbnail":"https://cdn.flowplayer.com/6684a05f-6468-4ecd-87d5-a748773282a3/i/v-i-a…","video_id":"adca9bde-51c4-49ad-9385-7a81fcb65c71","player_id":"8ca46225-42a2-4245-9c20-7850ae937431","provider":"flowplayer","video":"Restriction ...