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in 1660, the worlds oldest scientific academy, The Royal Society was founded.
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Make Invisible Ink
You will Need:
- Baking soda or lemon juice
- Paintbrush or swab
- Measuring cup
- Purple grape juice (optional)
Health and Safety: Be careful is heating up the paper, you don’t want to set it alight! Ensure you have adult supervision and a way of extinguishing flames at hand.
What to Do:
- Mix equal parts water and baking soda.
- Use a cotton swab, toothpick, or paintbrush to write a message onto white paper, using the baking soda solution as “ink.”
- Allow the ink to dry.
- With adult help, heat the paper by ironing it. The baking soda will cause the writing in the paper to turn brown.
- Another method is to paint over the paper with purple grape juice. The message will appear in a different colour. The grape juice acts as a pH indicator that changes colour when it reacts with the sodium bicarbonate of baking soda, which is a base.
How does it work?
- Writing a secret message in baking soda solution slightly disrupts the cellulose fibres in paper, damaging the surface.
- When heat is applied, the shorter, exposed ends of the fibres darken and burn before the undamaged sections of paper.
- If you apply too much heat, there’s a risk of igniting the paper. For this reason, it’s best to use either the grape juice chemical reaction or else apply a gentle, controllable heat source.
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Try some other activities from our STEM@Home section