What you’ll need
- two or three cotton swabs
- paper (try different types, they don’t all work equally well)
- 1 – 1.5 teaspoons of baking soda (= sodium hydrogen carbonate; usually found among baking products in stores)
- 100 ml hot water
- measuring cup
- iron (use only with the help of an adult)
How to do it
What's the secret?
Soda solution is slightly alkaline. When heated, sodium hydrogen carbonate becomes more alkaline and attacks the cellulose in the paper. So where you wrote using the baking soda “ink,” the paper is more sensitive and turns brown more easily in the heat.