Invisible ink has been used for centuries to convey secret messages. For example spies and secret lovers have written letters which were unreadable until they were decoded by someone who understood the message.
Many different substances can be used to create invisible ink. They can often only be seen after being exposed to a light or chemical.
Some of these invisible pens are only visible in certain conditions, like when heated or exposed ultraviolet light. Some invisible inks are only visible when exposed to a certain wavelength of infrared.
How to See Invisible Ink With Glasses
Some inks are only visible with special glasses which block certain wavelengths. This is particularly useful when creating barcodes with infrared ink (IR), which is difficult to read with the naked eye.
The best way to see invisible pens is with glasses which block a certain range of wavelengths. For example, UV or infrared pens. These glasses can be found at your local pharmacy or online.
Write Your Messages With Invisible Ink
Use your scientific knowledge to find out how certain substances can act as invisible inks. Change their conditions, like when they are heated or treated with chemicals.