Have you ever wanted to write a letter to someone but wanted to make sure no one else reads it? Would you like to make any letter or picture only visible by black light? The tutorial below presents a way to print with “invisible” ink, so you could create some spy-like documents.

By using an old printer cartridge and replacing the yellow ink, you would be able to print letters that would appear blank. As seen in the video, the document that was previously visible turned completely invisible when using this method.

The accomplice to the “crime” would be able to decipher and actually see the words, diagrams, or special codes only by the use of a black light.

If you try this out, let us know how it worked, and what kind of documents did you decide to make secret.

Via: Lifehacker