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 visible with special infrared camera.
These liquids include lemon juice and other liquids, such as milk, cola or vinegar. These organic inks can be revealed by exposure to heat, such as from an iron or light bulb. Some invisible inks use chemicals such as laundry detergents or soaps. They can be revealed with a developer solution. Spies used invisible inks which could be developed using heat or iodine. Some were even able be revealed by UV 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. The ink can also be viewed through a special lens or filter, which is often used to view the yellow dots on color lasers printers.
Some invisible inks can be revealed with ultraviolet (UV) light, and a pair of sunglasses that are labeled as UV protected may be able to help you see them. These sunglasses are designed to block most UV rays. This includes UV-A rays and UV-B. However, some invisible inks can be revealed by exposure to UV light, so it’s important to know what type of invisible ink was used before trying to read it through a pair of sunglasses.