Observe fire safety rules when working with an iron and other heating devices. This effect can also be observed when sugar is heated it melts and turns dark, turning into caramel. As a result of these chemical reactions, the products of their breakdown are released, which color the paper brown, making the secret message visible.

We followed Rachelle’s suggestions to use cotton swabs and cardstock and it worked perfectly. I love simple activities and this one is perfect All you need to create invisible ink is lemon (or lime) juice and a heat source. When the sheet of paper with invisible ink is heated, the breakdown of citric acid, milk and kitchen soda takes place. lemon juice (any citrus will work) cotton swabs. We pass a heated iron over the sheet of paper, and after a while the writing appears in a bright brown color. Invisible ink substances vary and can be revealed by using heat, an acid or base or Ultraviolet (UV) light. George Washington and his spies used lemon juice as invisible ink during the Revolutionary War. To reveal the message, we just have to heat up the sheet of paper. Lemon juice like other substances has carbon compounds in it, these were absorbed by the fibers.

Several minutes later the letters dry out and the writing on the paper becomes completely invisible. Dip the brush into the first beaker and write with the liquid, and then with the liquids in the second and third beakers, leaving an invisible message on the paper. Then start to write secret messages on paper. Pour a little milk into the first, lemon juice into the second, and the baking soda solution into the third. For the experiment, we’ll need 3 small beakers.

Lemon juice ink