![]() There are several types of reactions that can be used to expose invisible ink including acid-base, oxidation-reduction, and heat reactions. The type of chemical reaction can vary, but they all result in a colored end product that makes the ink visible. All of the recipes are based on chemical reactions that make one of the components inside the ink visible. Since then, many different recipes for secret ink have been developed. Its purposes were manifold, ranging from plotting conspiracies or espionage to writing secret love letters. Invisible ink is an ancient invention and has already been used over 2,000 years ago. A similar reaction is possible with other acidic solutions such as blueberry juice or hibiscus tea. Your secret message gets revealed! Concentrated grape juice should have also made your message visible as the grape juice contains acids that reacted with the alkaline baking soda absorbed by the paper. When it comes in contact with an alkaline or basic substance such as the baking soda on the paper, it turns from yellow to a deep red. This most likely changed when you painted the paper with the turmeric solution as turmeric changes color depending on if it is in an acidic or alkaline environment. 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.
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