Plant Dyes - Colour Magic!

Like cars, plants have indicators too...

The dye in the petals of some types of flower can change colour showing, or indicating, how healthy the plant is.

We can crush the petals to get the dye out and use this dye to show (indicate) if a liquid is an acid or not.
  • Grind a cup of darkly coloured petals (violet pansies are good) in a shallow dish with a little water. The back of a spoon can be used.
  • Pour the dye/juice into a clean jar leaving the lumpy bits behind in the dish
  • Store the dye in the fridge if you want to use it for a few days.
Try any darkly coloured petals or juice from vegetables and fruit. Beetroot juice, red cabbage, blueberrires and even a strong cup of tea works. Don't get the indicator dye on your clothes or furniture!
  • Take careful note of the colour of your indicator. This is the colour when it is neutral
  • Pour a little of your indicator dye into glass and add a few drops of vinegar. Did it change colour? If so, this is the colour for something that is an acid
  • Do the same again with another clean glass and add a little automatic dishwashing powder. Did it change colour? If so, this is the colour for something that is an alkali (or base)

Now lets have some more fun!

  • PREDICT: Ask your students "What will happen when I add a few drops of lemon juice to a fresh sample of my plant indicator? Will it change to show it is an acid, an alkali or is it neutral?"
  • OBSERVE: Watch what happens when your test liquid is added and well mixed.
  • EXPLAIN: What does this show us? (seniors might like to consider carrying out a titration to determine the Vitamin C content of lemon juice)
Try water, milk, lemon juice, Coca Cola, and rainwater. You can write down what you found out and try other liquids - but check with an adult first if its OK! Always wash out any kitchen glassware properly afterwards.



  1. Read more about acids here...
  2. Keep some of the concentrated dye for another experiment with electricity
  3. Use the juice from tea leaves to make another dye, a type of ink.
  4. The interactive pages...identify these pieces of lab equipment
  5. The interactive pages...weird metals and gases hide in this Periodic Table

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