

It gets absorbed by the paper similarly to the lemon juice and once dried isn't visible anymore (although you might have noticed some baking soda powder residues on the paper, which you can wipe off easily). The baking soda on the other hand is alkaline or basic. This oxidation reaction yields brown substances which make your secret message visible. This process releases carbon which oxidizes when it comes in contact with air.


Carbohydrates don't like heat and therefore when you use the hot iron on the paper with your secret message, the carbohydrates start to carbonize. At the same time, the carbohydrates from the lemon juice-like the citric acid-are absorbed into the paper. When you write on the paper with lemon juice, the acid weakens the fibers within the paper, and it starts to decompose. Lemon juice is a relatively strong organic acid as it contains citric acid. Were you able to reveal your secret message with both invisible ink methods? You should have been! Applying heat to the paper with lemon juice should have made your secret message visible. Wash your hands and clean your work surface. Let the paper dry and dispose it in the recycling bin. Discard of all your solutions in the sink.
