What it shows
A message written in baking soda water dries invisible, but a wash of turmeric water or purple grape juice turns the writing a different colour because baking soda is a base and these juices are indicators. No heat or flame is needed.
The science
Baking soda is a mild base. When it dries on paper it is invisible because it is white like the paper. Turmeric and grape juice contain natural indicator dyes that change colour where they touch a base: turmeric turns reddish brown and grape juice turns greenish blue. The dye only changes where the writing is, so the message appears in a new colour on a plain background.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- 2 teaspoons baking soda in 4 teaspoons water
- A cotton bud or a thin paintbrush
- White paper, 3 sheets
- Turmeric water (a pinch of turmeric in 2 spoons water) or dark grape juice
- A sponge or a wide brush
- Newspaper to protect the table
Safety
For this project: Turmeric stains, so wear old clothes and work over newspaper. Nothing is tasted once used as ink.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
7 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Stir the baking soda into the water until most of it dissolves; a little left at the bottom is fine.
Dip the cotton bud in the solution and write a short message on the paper, pressing lightly.
Let the paper dry fully in the air or in the sun; the writing should vanish.
Dip the sponge in the turmeric water and wipe it once across the paper in one direction.
Watch the hidden message appear in reddish brown within a few seconds.
Try the second sheet with grape juice instead and compare the colour of the revealed message.
On the third sheet write with plain water and reveal it with turmeric to show that the baking soda, not the water, causes the colour.
What you should see
The baking soda message appears clearly in reddish brown with turmeric or greenish blue with grape juice, while the plain water control shows nothing.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Why is the dried message invisible?
Dried baking soda is white, the same colour as the paper.
2What does the turmeric do?
It is an indicator that turns red brown where it touches the baking soda, which is a base.
3Would lemon juice ink work with turmeric?
No, lemon juice is an acid and leaves turmeric yellow.
4Why write a message with plain water too?
It is a control that proves the colour comes from the baking soda, not the wetting.
Take it further
Reverse the trick: paint a sheet with turmeric water first, let it dry, then write with baking soda solution to get instant red writing.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
Science projects
Easy Science Projects for Class 1 to 5
Simple, safe projects young children can make with a little help
Science projects
Safe Chemistry Projects for School
Experiments and models with kitchen materials and proper safety