The perfect gift for children is invisible ink. It’s a fun activity that will keep kids entertained for hours. The pens are easy to use and have great longevity. The pens are available in bulk, so you can always have one on hand. It is not just a gift for kids, but it’s also a great tool for adults.

Invisible ink is a very old technology. It dates back to the 1BCE, when Pliny recorded that milk from the tithymalus was used to make legible inscriptions. It was popularized during the Renaissance when many politicians and lords began using it as a way to communicate secretly. With the advent of war, invisible ink was further developed. German spies used simple citrus juice for writing messages that could be revealed only by steaming. The British censors soon caught on and employed systems of steaming all letters to see if they were hidden in invisible ink and then reading the hidden message.

There are two main types of invisible ink: organic fluids and sympathetic inks. Organic invisible inks can be made with common household items like lemon juice or vinegar, wine, onion juice, and even bodily liquids. These inks work because they change the fibers in the paper that they are written on, so they burn at a low temperature and turn brown quicker than the surrounding papers. You can reveal them by heating the paper in an oven, on a hot iron or by holding it close to a light bulb.

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