History Main / InvisibleWriting

* One ''Franchise/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.

* One of the ''BillyBunter'' 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.

CondensationClue and WritingIndentationClue are subtropes. See also SeeTheInvisible on ways to make things visible.

* An episode of ''Hetty Feather'' has a new Foundling (Eliza) arrive at the hospital and it turns out she stayed with the same foster family as Hetty. Hetty learns from Eliza that her foster brother mentioned the secret squirrel house they used to play at and that her foster brother did not mention Hetty to Eliza at all, leading Hetty to think that he has forgotten about her. When Hetty's friends learn of this, they have Eliza write a letter home, with the line "I hope you are reading this by your lovely warm fire" and on Eliza's letter, they write a message using lemon juice, which won't show up on the paper unless it is held up to a fire, to tell the foster brother what has happened to Hetty.

* ''Film/GoneInSixtySeconds2000'': Memphis (NicolasCage) and his crew use this to hide a list of target cars, from Detective Castlebeck. The writing is only visible under "black light".

** the spell Arcane Mark can functionally be an invisible ink. The campaign setting {{Eberron}} notices this, and [[{{Deconstruction}} uses it on documents to increase the difficulty of forging]].

* ''Manga/KeroroGunsou'' has a chapter where he receives a message from his superiors that had to be revealed by rubbing an eraser on it. In the anime, the message also gets partially revealed due to entry through the atmosphere.
* In ''Manga/OuranHighSchoolHostClub'' Tamaki's father sends him messages in invisible ink (made with lemon juice). The club believes that the messages come from the person sending them threatening letters and hilarity ensues.
* In ''Manga/{{Naruto}}'', the Uchiha tablet on first glance gives the basic informations regarding secrets of the Uchihas. But use your Mangekyou Sharingan or Rinnegan and you 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.
* In ''Manga/GugureKokkuriSan'', Kokkuri-san is transformed into a woman by a cursed box whose sole contents is a piece of paper reading "I told you not to open it," and immediately burns the paper. Kohina reveals a little later that words would appear on the paper if it's held up to the light (probably some form of watermark).

* Two short stories by Creator/AgathaChristie (one featuring HerculePoirot and one MissMarple), involve rich eccentrics writing their {{will}} in Invisible Ink, and challenging the heirs to find it.

* In ''[[{{Deryni}} In the King's Service]]'', Alyce de Corwyn gets a letter from her late father that appears to have a banal message about a bequest of family jewels, yet he left a second message [[spoiler: revealing that Vera Howard is really Alyce's twin sister]] that only becomes visible when Alyce activates her father's spell by kissing the wax seal.

* The idea of using citrus oils as in ''Film/NationalTreasure'' was a common means of sending covert messages through the end of the Cold War. [[DanBrowned While an oven was required]] to reveal the message in National Treasure, an ordinary incandescent light bulb is usually enough to reveal such messages.

* There's an inexpensive kind of pen whose ink can only be seen under ultraviolet light. Said pens are usually fitted with such a light on the cap, for checking mistakes.

Something that looks innocuous and featureless actually has some writing on it. You aren't able to see it with the naked eye: you'll need some way to reveal it.

May lead to FridgeLogic: if one uses an "invisible ink" to write, wouldn't the writer have a hard time writing it? (It may be handwaved by turning the text invisible after it was written, in some way.)

TruthInTelevision: this was a valid secret communication technique right until the 20th century, when UV lamps (a/k/a "Wood's Light", "black light") rendered it obsolete.

CondensationClue is a subtrope. See also SeeTheInvisible on ways to make things visible.

* In an early episode of ''WesternAnimation/RockyAndBullwinkle'' Natasha reveals a message that was in invisible ink by holding the paper in front of a candle: "Keel Moose." Boris drops a safe to land on Bullwinkle's head. After the CommercialBreakCliffhanger Natasha says that two more words have appeared: "Do Not." Boris races the safe to save Bullwinkle.
* This was also used in the ''WesternAnimation/GarfieldAndFriends'' episode "The Legend Of Long Jon". Garfield and Odie were reading from the journal of Jon's pirate ancestor Long Jon Arbuckle, when Odie started drooling on an apparently blank page, which causes writing to appear on the page. It turned out that Long Jon Arbuckle had written on the blank pages in invisible ink, telling about how he was able arrest some bandits that were carrying phony documents.

* A really {{Squick}}y example: fresh semen may be used as an invisible ink much as lemon juice may be applied. apparently all men can access a stock even if in a place where no lemons are available.
** Saliva does the job too, so you don't have to be male to improvise InvisibleWriting.

* One corpse from ''Series/CSI'' had InvisibleWriting all over its skin.

* A really {{Squick}}y example: fresh male sperm may be used as an invisible ink much as lemon juice may be applied. apparently all men can access a stock even if in a place where no lemons are available.

* ''VideoGame/{{Uncharted}} 2: Among Thieves'' has several maps, inscriptions, etc. showing the way to the legendary Cintamani Stone that are only visible in the blue light created by burning a special resin. [[spoiler: The resin is the congealed sap of a tree that grants great physical prowess and immortality, the true form of the Stone.]]

* In one episode of ''Series/TheOffice'', Dwight attempts to pass a secret message to the other salespeople by handing them letters with a second message written beneath the main text in invisible ink, hinting to them to expose the letters to heat to make the secret message visible. Of course, none of them bothers to do so. Dwight also cheerfully admits that the "invisible ink" in question is in fact [[{{Squick}} his own urine]].

* In the ''NancyDrew'' game ''The Haunted Carousal''; she helps out the bookkeeper with some puzzles that would reconnect her childhood (long story). One puzzle involved a piece of lemon scented paper that showed a message when ironed.

* ''Film/GoneInSixtySeconds2000''. Memphis (NicolasCage) and his crew use this to hide a list of target cars, from Detective Castlebeck. The writing is only visible under "black light".
* ''Film/WhoFramedRogerRabbit''. Mr. Acme was the inventor of the 'disappearing-reappearing ink' which would become invisible almost immediately, but become visible again through time. [[spoiler:Mr. Acme also wrote his will with it, leading it to be believed lost.]]

* ''TheCountOfMonteCristo'': the key to the colossal fortune was found in an old piece of paper used as a bookmark. When Faria tried to use it to light a candle, he noticed words forming on it and quickly extinguished it, but was arrested before he could find it.

* ''Film/GoneInSixtySeconds''. Memphis (NicolasCage) and his crew use this to hide a list of target cars, from Detective Castlebeck. The writing is only visible under "black light".

* 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 ''Literature/HarryPotterAndTheChamberOfSecrets'', the team initially thinks that Tom Riddle's diary was written with invisible ink, with Hermione trying spells and a magicked eraser called a "revealer" to try and make something visible. {{Subverted}}: [[spoiler:The diary contains Tom Riddle's memories in a very literal sense, and is capable of responding to written messages.]]
** In ''The Prisoner of Azkaban'', 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.

* Two Agatha Christie short stories, one featuring HerculePoirot and one MissMarple, involve rich eccentrics writing their will in Invisible Ink, and challenging the heirs to find it.