Hobbies And Interests
Edible Inks
Invisible inks can be made from a number of edible substances, which are usually developed using heat. The paper used needs to be fibrous in order for the ink to soak in, as glossy paper will not hold the ink properly. Lemon juice, onion juice, cola and honey are among the substances that can be used. Dark liquids such as cola need to diluted with water so the color does not show on the paper. Once a message is written, heat the paper with a hair dryer, near an open flame or with an iron to cause the sugars in the liquid to turn brown and the letters to become visible.
Chemical Inks
Some invisible inks can be made from chemicals that react with each other. A colorless liquid is used to write on the paper; often a quill, small paintbrush or cotton swab is best for application. A second chemical is then brushed over the paper, which will chemically react with the first and change color to reveal the writing. An example of the chemical type is the use of cerium oxalate as the ink and manganese sulfate, which will produce orange writing.
UV Light Inks
Some invisible inks can only be seen using ultra violet light. Certain liquids may appear clear in the light of the day but when placed under UV they will glow. A solution of starch can be painted onto a piece of fibrous paper and, once it dries, it is completely invisible. Running a UV light over the paper will cause the writing to glow and become visible. Another less-wholesome liquid that glows under UV is urine.
Ink-less Secret Messages
Sometimes you don't even need an ink to send a secret message. When writing on a note pad, if you press hard enough, the indentations of the words will transfer through to the sheets of paper below. By taking the first or second sheet below your original message, you can send that message, which is not visible in ink. The recipient merely has to rub the side of a pencil point gently over the paper and the indentations will be left white.