Suck lemon juice with a pen like ink, and then write it on a piece of white paper. There is no trace on the white paper. Light the lighter, put the paper on it, and the words will slowly appear.
Another method is to put a piece of wet paper on the glass or mirror, a piece of money paper on the wet paper and write on the dry paper with a ballpoint pen.
At this time, the words written on the dry paper will be printed on the wet paper. When it dries, there is no trace. If you want to read it again, just wet the paper.
Extended data:
The principle of invisible ink:
As invisible ink, colorless transparent solution prepared with acid-base solution, indicator, precipitant, oxidant, reducing agent, mixed solvent or catalyst and luminescent agent must be written on filter paper treated with special drugs, so that fonts with different colors will appear due to acid-base neutralization, precipitation, redox, formation of complex ions or complexes or catalysis.
If potassium iodide solution, sodium thiosulfate solution and potassium thiocyanate solution are mixed into a comprehensive invisible ink, yellow font (PbI2), brown font (I-) and red font [Fe(SCN)2+] can be written on the filter paper treated with lead nitrate solution, iodine solution wave and ferric chloride solution respectively.
Baidu encyclopedia-invisible ink