Editing Invisible ink (section)

== General application and use ==

Invisible ink can be applied to a writing surface with a specialty purpose [[stylus]], [[Rubber stamp|stamp]], [[fountain pen]], [[toothpick]], [[calligraphy pen]], [[Cotton swab]], or even a finger dipped in the liquid. Once dry, the written surface looks as if it were blank, with a similar texture and reflectivity as the surrounding surface.

The ink can be later made visible by different methods according to the type of invisible ink used. The ink may be revealed by heat or by application of an appropriate chemical, or it may be made visible by viewing under [[ultraviolet light]]. Inks which are developed by a [[chemical reaction]] may depend on an [[acid-base reaction]] (like [[litmus paper]]), reactions similar to the [[blueprint]] process, or any of hundreds of others. Developer fluids may be applied using a spray bottle, but some developers are in the form of vapor, e.g. [[ammonia]] fumes used to develop [[phenolphthalein]] ink.

There are also toy invisible ink pens which have two tips—one tip for invisible ink writing, and another tip for developing the ink. Invisible ink is sometimes used to print parts of pictures or text in [[book]]s for children to play with, always including a "[[decoder pen]]" which is used to show the invisible parts of texts or pictures, thus revealing answers to questions printed in regular ink or completing missing parts of pictures.

[[File:Artlung_blacklight_messages.jpg|thumb|A common task in [[escape room]]s is assemble an eye-safe [[blacklight]] torch to reveal [[steganography|messages in invisible ink]] ]]
Security marker pens or [[UV marker]]s with fluorescent ink that glows when illuminated with a UV light is often used to invisibly mark valuable household items in case of [[burglary]]. There are specialty security maker pens formulated for writing on non-porous surfaces such as [[glass]], [[plastic]], [[metal]], etc. The mark can be read by using a [[blacklight]] or other UV light source. Security marker pens can be obtained commercially and are widely used as a crime countermeasure.

Some commercially available invisible inks glow very brightly, in a variety of colors, under [[ultraviolet]] light. This makes them suitable for use in readmission such as hand stamping.

There are some invisible ink types that can only be invisible when applied to certain types of surfaces, but are still visible on others.

Some vendors now offer invisible ink for use in computer [[inkjet printer]]s.  Such inks are usually visible under [[ultraviolet]] light. Typical uses include printing information on business forms for use by the form processor, without cluttering up the visible contents of the form. For example, some [[United States Postal Service]] mail sorting stations use UV-visible ink to print bar codes on mailed envelopes giving routing information for use by mail handling equipment further down the line before delivery.

An [[End-to-end auditable voting systems|E2E]] voting system called [[Scantegrity II]] uses invisible ink to enable the voter to obtain a confirmation code only for the voted selection.<ref>{{cite journal |last=Chaum |first=David |author-link=David Chaum |author2=Richard Carback |author3=Jeremy Clark |author4=Aleksander Essex |author5=Stefan Popoveniuc |author6=Ronald L. Rivest |author7=Peter Y. A. Ryan |author8=Emily Shen |author9=Alan T. Sherman |title=Scantegrity II: End-to-End Verifiability for Optical Scan Election Systems using Invisible Ink Confirmation Codes |journal=Proceedings of USENIX/ACCURATE EVT |year=2008 |url=http://www.usenix.org/event/evt08/tech/full_papers/chaum/chaum_html/ |url-status=live |archive-url=https://web.archive.org/web/20081203123100/http://www.usenix.org/event/evt08/tech/full_papers/chaum/chaum_html/ |archive-date=2008-12-03 }}</ref>