There are many ways of detecting or revealing invisible inks. Some can be revealed by light, while others require a chemical reaction or heat to become visible. Some are even able to be seen by special infrared cameras.
These liquids include lemon juice and other liquids, such as milk, cola or vinegar. These organic inks will be revealed when exposed to heat from an iron, light bulb or other source of heat. Some invisible inks use chemicals such as laundry detergents or soaps. They can be revealed with a developer solution. Spies often used invisible inks that could be developed with heat or iodine, and some were even able to be revealed by ultraviolet light.
UV ink (an invisible ink) is used to print information on printers, such as the printer’s serial number or the date and time of a print. This ink can be viewed using a special filter or lens. It is sometimes used to see the yellow dot code on color laser printers.
UV-protected glasses can help you detect some invisible inks. These sunglasses block out the majority of UV rays including UV-A and UVB rays. Exposure to UV light can reveal some invisible inks. Therefore, it is important to know the type of invisible ink before trying to see it through sunglasses.