Anyone who has watched a spy film knows that secret messages are often sent between agents using invisible pen. It’s a fun way to pass along a note without being noticed, and it’s even possible for kids to create their own invisible ink. All you need are a few common household items and a black light or UV light to reveal the invisible message.
During World War II the SOE used ink invisible to communicate with agents working behind enemy lines. They identified the properties of an ideal invisible ink: Must mix easily with water and should not leave a noticeable smell or deposit crystals on the paper. Must not be heated (as with lemon juice) or react to other chemicals such as iodine. It should also not stain the paper.
Inks that glow when exposed to UV light, specially formulated inks, are used widely. They’re especially useful for marking products during manufacturing and for tickets for events. Some passport photos are marked with tiny yellow dots visible only through certain types of cameras.
These sunglasses allow players to see invisible ink marks that are on the back of marked cards. These sunglasses are not like other invisible ink devices such as poker analyzers. They look like regular sunglasses, so other players won’t recognize them as cheating devices. Moreover, the appearance of these sunglasses can be changed according to your preference so you can choose them based on your playing environment.