History Main / InvisibleWriting

CondensationClue and WritingIndentationClue are subtropes. See also SeeTheInvisible on ways to make things visible. For examples where invisible ink gives something else invisibility, see InvisibilityInk.

** In ''Literature/HarryPotterAndThePrisonerOfAzkaban'', Fred and George introduced the Marauder's Map, which doesn't just show the map of whichever building the holder is in, but also shows the footsteps of people. It looks like just an empty sheet of old paper... unless you know the chant for activating it.

'''Pollock''': Should've joined my troop. We'd have waived it.

'''Yasmin''': [[SacrcasmMode I flunked the physical]].\\

* ''Film/KnivesOut:'' Harlen writes messages to his adult daughter Linda in invisible ink, simply because it amuses both of them.

* A really {{Squick}}y example: Fresh semen may be used as an invisible ink much as lemon juice may be applied. Apparently, [[ADateWithRosiePalms all men can access a stock]] even if in a place where no lemons are available.

* ''{{Film/Constantine}}'': Angela and her sister Isabela left hidden messages on windows and mirrors when they were kids, visible only when fogged by their breath. Isabela left her sister one last message before she was DrivenToSuicide.

* The bracelet given to apprentice white witch Susan, in Creator/AlanGarner's fantasy novel ''The Moon of Gomrath'', is apparently of plain silver with nondescript black inlay. But in times of great need, it manifests readable writing, which when spoken by her becomes a spell of great potency and confounds the creations of evil.

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* In ''Webcomic/GirlGenius'', the librarians at the Incorruptable Library [[https://www.girlgeniusonline.com/comic.php?date=20160201 shine a UV light]] at Van Rijn's notebook (using the same wavelength as the Storm King's lightning) to reveal an entirely new work that Agatha had missed completely. He apparently used multiple methods to conceal his work including "phasing ink, momentum writing, four-dimensional cryptograms, [[TheLastOfTheseIsNotLikeTheOthers and lemon juice]]". Agatha later gets a bit over-enthusiastic about finding the hidden writings, and discovers that if you study the leather cover ''really'' closely, it contains instructions for building a cow.

** The Unseen University faculty includes the Reader in Invisible Writings.

A simple example is writing a messsage with citrus juice. Once it dries, the print becomes invisible. One must warm the paper to reveal the words. Other times, you will need specialized equipment such as a fluoroscope or a chromatic filter to view the writing. In fantasy worlds, magic or GreenRocks are needed to make the writing visible. Possibly, the writing can only be read by a specific person, or at a specific time frame or location. Otherwise, the writing is invisible.

* In ''VideoGame/FinalFantasyVIII'', when you slowly make your way towards [[spoiler: the blue pillar holding Bahamut,]] who tells you to turn back... If one manages to successfully make it [[spoiler: to said glowing pillar]], you have to fight '''two''' [[EliteMooks Red Dragons]] and give the proper answers after defeating each one before he/she angrily asks why they're fighting against him. [[spoiler: The true answer to the third and final question is completely invisible, the resultant answer shown is truly soul-chilling to first-timers, to say the least...]]

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* Cale Tucker, TheHero of Creator/DonBluth's ''WesternAnimation/TitanAE'', receives a ring from Captain Korso. The ring has been coded to Cale's genetics so that it reveals a star map on Cale's hand. As a further safeguard, the map's pointer shifts direction while Cale is standing on a platform on Sessarim.

* One of the ''Literature/Greyfriars'' stories had a main character receive a letter from a missing relative, asking whether he remembered a particular party trick. He doesn't, but the letter is left out in the hot sun for a while, which reveals the real message saying that the relative has been kidnapped.

* ''Film/NationalTreasure'': A secret message was written on the Declaration of Independence with invisible ink that was revealed with heat. Further clues were embedded in the Declaration of Independence, visible only through a pair of glasses with switchable chromatic filters.
* In ''Film/NowYouSeeMe'', the Horsemen's New Orleans show seems to use some form of Invisible Ink which shows up under a flashlight.
* ''{{Film/Constantine}}'': Angela and her sister Isabela left hidden messages on windows and mirrors when they were kids, visible only when fogged by their breath. Isabela left her sister one last message before she was DrivenToSuicide.
* One ''Film/CharlieChan'' mystery ''Charlie Chan in Shanghai'' has some writing on a piece of linen. The glyphs appear to be Chinese, but Chan declares them as gibberish. He then points out that, despite plenty of writing paper available, the marks were made on cloth. Chan rinses the linen in a bowl of water, which washes away some of the ink, but leaves the true message in broken Roman letters intact.
* In ''Film/PacificRim'', Newton tracks down Chau's kaiju-parts dealer by spotting hidden symbols on signposts with a UV penlight.
* ''Film/KnivesOut:'' Harlen writes messages to his adult daughter Linda in invisible ink, simply because it amuses both of them.

* In ''Manga/{{Naruto}}'', the Uchiha tablet on first glance gives the basic informations regarding secrets of the Uchihas. But someone using their Mangekyou Sharingan or Rinnegan and will see even more details regarding the history of the ninja world. Such as the history of Senju and Uchiha war and the origin of the Ten-tails.