Editing Invisible ink (section)

== Disappearing inks ==

Inks that are visible for a period of time without the intention of being made visible again are called disappearing inks. They typically rely on the chemical reaction between [[thymolphthalein]] and a basic substance such as [[sodium hydroxide]]. Thymolphthalein is normally colorless, but turns blue in solution with the [[Base (chemistry)|base]]. As the base reacts with carbon dioxide (always present in the air), the [[pH]] drops below 10.5 and the color disappears. Pens are also available whose inks can be thoroughly erased by swiping a special pen over the original text. Disappearing inks have been used in gag squirtguns, for limited-time secret messages, for security reasons on non-reusable passes, for fraudulent purposes, and for dress-making and other crafts where measurement marks are required to disappear.<ref>{{cite web |url=https://www.cfo.com/accounting-tax/2002/04/bad-sign/ |work=[[CFO (magazine)|CFO Magazine]] |date=April 1, 2002 |title=Bad Sign }}</ref><ref>[http://www.tv.com/exhibit-a/schemes-and-dreams/episode/880177/recap.html Exhibit A: Schemes and Dreams Recap] {{webarchive|url=https://web.archive.org/web/20090115082110/http://www.tv.com/exhibit-a/schemes-and-dreams/episode/880177/recap.html |date=2009-01-15 }} TV.com</ref><ref>[http://www.joann.com/dritz-quilting-purple-fine-point-disappearing-ink-marking-pen/4792438.html Dritz Quilting Fine Point Disappearing Ink Marking Pen] {{webarchive|url=https://web.archive.org/web/20161227060720/http://www.joann.com/dritz-quilting-purple-fine-point-disappearing-ink-marking-pen/4792438.html |date=2016-12-27 }}</ref>