Brain Teasers Optical Illusions Puzzle Hunts Codes & Ciphers Mechanical Puzzles
Personal Links
Browse Teasers
Search Teasers

Invisible Ink

Science brain teasers require understanding of the physical or biological world and the laws that govern it.


Puzzle ID:#9525
Fun:*** (2.38)
Difficulty:** (1.13)
Submitted By:alintanfern
Corrected By:Dave




There are two secret agents who want to send letters to one another but think that someone might try to read them. The first agent came up with an idea to send a letter to the other agent by writing with invisible ink. He then put the letter in his mailbox for delivery. When the other agent received the letter, he opened it and began to read its contents. How was it possible for the first agent to write with invisible ink and how was the other agent able to read it?

What Next?


See another brain teaser just like this one...

Or, just get a random brain teaser

If you become a registered user you can vote on this brain teaser, keep track of
which ones you have seen, and even make your own.



Jan 14, 2003

fun science project for kids! it also works with milk and vinegar, if you don't have lemon juice handy. you can also reveal the secret lemon message by spreading iodine or red cabbage juice over the paper. Also, a safer way than using a flame (read: flammable) is to hold the paper over a light bulb or to iron it.
Jan 14, 2003

Bluetwo, 007 does not worry about the safety of using flames! lol Well you two have just about ruined the spy business by giving up one of there best kept secrets. Just kidding, I knew about this one since I was a kid.
Jan 17, 2003

the spy could also write using white liquid paper and the other spy could hold that to a lightbulb too.
Jan 17, 2003

I highly doubt it jonny. As any college student can tell you, white-out leaves a very telltale mark and is VERY easily seen.

My favorite method for sending a sensitive message is on flash paper... once the person has seen the info they need, all they do is touch a match to it and FOOM it's gone in the blink of an eye. It's not invisible writing, but it's fun anyway.
Jan 18, 2003

has somebody torn the"?" key off his keyboard?
Feb 18, 2003

the message could be sent telepathically -- therefore making it invisible to the naked eye.
Aug 01, 2004

The agent opened the letter and began to read it, which would indicate to me that it was readable before using the heat lamp. Perhaps it sat in the mail box to long in the sun?
I hear you can see Cat urine with a black light.
Sep 02, 2006


Anyway, you could also use salaiva(spit). It's kind of nasty, but it does work.
Oct 29, 2007


Back to Top

Online Now
2 users and 607 guests

Users In Chat
Follow Braingle!
Tap into all 20,000+ of our brain teasers, riddles and puzzles on your iPhone or iPad.
Braingle in the iTunes App Store
Copyright © 1999-2017 | FAQ | Widgets | Links | Green | Subscribe | Contact | Privacy | Conditions | Advertise | Braingle Time: 3:54 am
Sign In Create a free account