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Eat the colours of the rainbow!

Updated: Apr 19, 2021

There is an old adage that to maintain good health, you should eat the colours of the rainbow. To my kids’ dismay, it doesn’t mean a variety of different coloured candy treats like gummy bears or jujubes. In this activity, we explore what it means to “eat colours”, and what actually makes colours in the natural foods that we eat? These colours come from pigments which are simply the chemicals that create colours. Did you know that blueberries are actually comprised of purple pigments called anthocyanins? Maybe we should rename them purpleberries from now on!

Never has my son been so eager to pick kale from our garden!

This science activity is really easy for you to do at home with materials you probably already have. In fact, my son and I decided to try it during the pandemic lockdown, and since we weren’t going out of the house for groceries at the time, we had to improvise some of the materials. We had fun using carrots, kale and blueberries in this experiment – but any really colourful produce that is easy to extract the juice from would be good, e.g. peppers, oranges, blackberries, raspberries, etc. Some produce wouldn’t work well (e.g. bananas or apples).

Squishing blueberries

Here is a useful info sheet, click here to find out about the materials required, instructions for how to extract the juices, and how to set up your chromatography column (basically a “writing in colour”) that the pigments will travel upwards on. You can use cut up strips of coffee filters, or we had to use watercolour paper because I had run out of coffee filters.

For us, squishing blueberries in a garlic press was a lot of fun. We used a juicer for the carrots and kale, but a garlic press or a nutmeg grater would work too – you would have to then squeeze the liquid out of the minced produce.

We used toothpicks to dab the extract

We used toothpicks to dab the extract onto our watercolour paper. This took quite a lot of patience – we tried drying it with a hair dryer so we could quickly reapply since you need quite a thick dollop but have to let it dry in layers. The hairdryer was too powerful, so we cheated and after each dab, we placed the columns onto a cookie sheet and into a 175degree oven for a few minutes. (Have an adult help you with this if you go this route!)

Patience…give the colours time to travel up the columns. We had fun checking them every few hours.

Colours travel up the columns
We were so happy to see the results!

Exciting results! Look at the pigments and how they travelled up the columns! My favourite is the blueberry in the middle – you can see dark and light purple pigments (called anthocyanins) at the bottom and half way up, and green (called chlorophyll) on top.

After we finished the experiment, we decided to try to paint with the green kale juice – it was fun, but it should be painted in several layers that you let dry in between so the colour is darker. I attached a pic of our artwork below.

Happy experimenting!

Painting with Kale! My son said it is the best way to use kale. (He’s not a big fan of the taste!)

Want to try this on your own? Download the instructions below:

Download PDF • 4.53MB

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