Invisible ink offers an interesting way to conceal messages that are only revealed under certain circumstances. These conditions can include a chemical reactions, heat, or viewing under ultraviolet light. There are many ways of making invisible ink. Some include using soapy water or laundry detergents that contain brighteners.
The most common inks that are invisible are organic fluids, which change color upon heating. These types of inks can be rendered visible by heating the paper with an iron or a hair dryer, or by exposing it to a 100-watt light bulb. Some inks are also made of non-organic materials that change color when exposed to acid, such as methyl ethyl ketone and nitrocellulose.
To decode an invisible message, the person who wrote it must be able to find the right chemicals to react with the ink. The telltale signs of this type of writing are pen scratches, or the appearance of abnormalities in the paper. These telltales alert a censor that a hidden message is present.
The use of clear sunglasses that can read marked cards is a great way to see invisible ink marks. These sunglasses have the same appearance as normal sunglasses, so no one can suspect that you are using them to cheat in poker games. Some people use these sunglasses to play poker at home with friends, because they can be used anywhere.