heat source (like a candle or an incandescent light bulb)
Gather your materials!
Squeeze the juice of the lemon into a small bowl.
Some seeds may fall in, but you don’t need to fish them out.
Using the cotton swab as a pencil, write a secret message on the paper. Then, let the paper dry completely.
Bring your heat source close to the paper and watch as your secret message magically begins to appear!
Lemon juice is mostly made of a variety of sugars, acids, and water. Normally, lemon juice is mostly clear, so when you dilute it even further in water, and paint that mixture onto some paper, you can't see it. However, heating up lemon juice causes some of its sugars to react with oxygen in the air (oxidation), which turns these sugars brown. Acids in the lemon juice can also react with fibers in the paper to make more sugars, which again turn brown in the heat. Your invisible ink might seem like magic, but really, it's all just chemistry.
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