Materials Required
- White paper
- 2 bowls
- Spoons for mixing
- Baking soda (1 tablespoon)
- Turmeric powder (1 teaspoon)
- Q-tips or small brushes for writing
- Larger brush for revealing
- Rubbing alcohol or any alcohol 40% or higher (0.5 cup) - water works but colors are less bright
- Water (0.5 cup)
- Table covering (newspapers or plastic sheet)
Safety Warning
Important! Turmeric stains clothing, surfaces, and skin. Please be careful when using the turmeric solution. Cover your work area and wear old clothes or an apron.
Instructions
- Prepare the invisible ink (baking soda solution):
- Mix 1 tablespoon of baking soda into 0.5 cup of water in a bowl
- Stir well until the baking soda is almost fully dissolved (this may take a few minutes)
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Keep stirring occasionally during the experiment as baking soda settles
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Create your secret message:
- Use a Q-tip or small brush to write or draw on paper with the baking soda solution
- Write your secret message or draw invisible pictures
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Set the paper aside to dry completely (15-30 minutes)
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Prepare the revealing solution (turmeric indicator):
- While waiting for the paper to dry, mix 1 teaspoon of turmeric powder into 0.5 cup of rubbing alcohol in the second bowl
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Stir very well until the turmeric is dissolved and the liquid is bright yellow
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Reveal the secret message:
- Once your invisible ink is completely dry, use the larger brush to paint over the entire paper with the turmeric solution
- Watch as your secret message appears in bright red/pink!
- Let it dry to preserve your revealed message
What's Happening?
pH Indicators:
Substances can be acids, bases, or neutral. This experiment uses the same chemistry as the cabbage pH indicator, but with a different natural dye.
The Chemistry of Turmeric:
Turmeric is a pH indicator thanks to a molecule called curcumin. Curcumin naturally changes color depending on the pH of its environment:
- In acidic solutions: Curcumin stays yellow
- In neutral solutions: Curcumin stays yellow
- In basic (alkaline) solutions: Curcumin turns red/pink
Why Your Message Appears:
1. When you write with baking soda solution and let it dry, baking soda crystals remain on the paper (invisible to the eye)
2. Baking soda (sodium bicarbonate) is a base with a pH around 8-9
3. When you paint the turmeric solution over the paper, the curcumin in the turmeric touches the baking soda
4. Where the turmeric meets the basic baking soda, it turns red/pink
5. The rest of the paper stays yellow because plain paper is neutral
This is the same principle used in some smart food packaging that changes color to show when food has spoiled!
Tips for Best Results
- Use rubbing alcohol instead of water for brighter, more vibrant colors
- Make sure your invisible ink is completely dry before revealing
- Keep stirring your baking soda solution while you write
- Work on a protected surface - turmeric really does stain!