# How Does Disappearing Ink Work?

**URL:** <https://boards.straightdope.com/t/how-does-disappearing-ink-work/6246>\
**Category:** Factual Questions\
**Created:** [January 15, 2000, 5:38pm UTC](https://boards.straightdope.com/t/how-does-disappearing-ink-work/6246 "2000-01-15T17:38:00Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![system](https://global.discourse-cdn.com/straightdope/original/2X/e/e489c3b7d8fce19c4b355dd4fc3f88cc39c34b87.png) [@system](https://boards.straightdope.com/u/system)\
**Post date:** [January 15, 2000, 5:38pm UTC](https://boards.straightdope.com/t/how-does-disappearing-ink-work/6246/1 "2000-01-15T17:38:00Z")

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Question posted at the request of Youngest Son, who has been running around the last few days squirting everything and everyone in sight with the stuff, and chortling hysterically as he watches it disappear (he’s 9).

-Melin

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**Author:** ![sly](https://avatars.discourse-cdn.com/v4/letter/s/e56c9b/32.png) [@sly](https://boards.straightdope.com/u/sly)\
**Post date:** [January 16, 2000, 6:58am UTC](https://boards.straightdope.com/t/how-does-disappearing-ink-work/6246/2 "2000-01-16T06:58:00Z")

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It operates on the principle of acid/base chemistry. The reason the “ink” is blue to start with is because a particular molecule in the solution, thymophthalein, is blue in solutions that are basic. That same molecule is colorless under neutral conditions.

When disappearing ink is sprayed on your clothes, part of the solution evaporates  
(the part is normally an alcohol of some sort), and instead of being basic the result is a neutral residue (left-over solid). With the evaporation, the thymophthalein is no longer experiencing basic conditions so it  
changes colors and “disappears”.

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**Author:** ![handy](https://avatars.discourse-cdn.com/v4/letter/h/b5a626/32.png) [@handy](https://boards.straightdope.com/u/handy)\
**Post date:** [January 15, 2000, 9:36pm UTC](https://boards.straightdope.com/t/how-does-disappearing-ink-work/6246/3 "2000-01-15T21:36:00Z")

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Pretty handy for writing checks at the bank, eh?

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**Author:** ![NanoByte](https://avatars.discourse-cdn.com/v4/letter/n/ecc23a/32.png) [@NanoByte](https://boards.straightdope.com/u/NanoByte)\
**Post date:** [January 15, 2000, 9:41pm UTC](https://boards.straightdope.com/t/how-does-disappearing-ink-work/6246/4 "2000-01-15T21:41:00Z")

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I had something to say, but I got some of that stuff in my brain. Sorry.

Ray

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LIFE: Those sparse nanoseconds between downloads of software upgrades.

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**Author:** ![Studi](https://avatars.discourse-cdn.com/v4/letter/s/5daacb/32.png) [@Studi](https://boards.straightdope.com/u/Studi)\
**Post date:** [January 15, 2000, 10:12pm UTC](https://boards.straightdope.com/t/how-does-disappearing-ink-work/6246/5 "2000-01-15T22:12:00Z")

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Magic.

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“What contemptible scoundrel has stolen the cork to my lunch?” --W.C. Fields

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**Author:** ![funneefarmer](https://avatars.discourse-cdn.com/v4/letter/f/9fc348/32.png) [@funneefarmer](https://boards.straightdope.com/u/funneefarmer)\
**Post date:** [January 15, 2000, 10:34pm UTC](https://boards.straightdope.com/t/how-does-disappearing-ink-work/6246/6 "2000-01-15T22:34:00Z")

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Anything that limits Nano to one line must be magic…

Sorry obvious cheap shot, couldn’t help it.

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**Author:** ![Manduck](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/manduck/32/256_2.png) [@Manduck](https://boards.straightdope.com/u/Manduck)\
**Post date:** [January 16, 2000, 7:09am UTC](https://boards.straightdope.com/t/how-does-disappearing-ink-work/6246/7 "2000-01-16T07:09:00Z")

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_Your obligatory Simpsons quote (well, paraphrase):_

There’s no mystery about disappearing ink - it simply disappears! Now let’s have no more curiosity about this bizarre coverup.