English version

invisible ink

From Longman Dictionary of Contemporary Englishinvisible inkinˌvisible ˈink noun [uncountable] 🔊 🔊 TCSECRETink that cannot be seen on paper until it is heated, treated with chemicals etc, and is used for writing secret messages
Examples from the Corpus
invisible inkA newly created invisible ink makes the animals disappear with the heat of your body.Vietcong couriers slipped into Saigon to pick up his reports, which he wrote in invisible ink made from starch.
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