In this simple STEM activity, children learn about colour mixing and separation in a hands-on way. Using a coffee filter and black marker, discover the different colours that make up black ink.
You Will Need
Filter paper
Water-based black marker
Small glass
Water
Prior Discussion Questions
What is colour? What do you know about colour?
Some colours are made up of other colours – can you name any colours that are made from mixing two colours together?
How do you make purple? How do you make green?
What about black? We’re going to find out what colours can make black.
1. Using a water-based black marker, draw line 2–3cm thick, approx. 3cm from the bottom (pointy-end) of the coffee filter. Repeat on other side of filter.
2. Put some water in your glass, about 2cm deep.
3. Place the coffee filter in your glass making sure the pointy-end is touching the water but the ink is not.
4. Watch as the water travels up the filter paper, about 1–2mins. The black ink separates to reveal the colours that were used to make it – this process of separation is called chromatography.
5. Remove the filter paper from the glass and lay out to dry.
6. Look at the filter paper – what colours have appeared from the black marker?
Post-Activity Discussion Questions and Activities
How many colours can you see on the paper?
What happened to the black line when it got wet?
Why do you think the black ink changed into different colours?
Were you surprised to see different colours from the black marker? Why or why not?
Which colour is there most of? Why do you think that is?
Try this experiment again with another coloured marker to compare results. What colours appear? Are they the same as from the black marker or different? Why?
Learn the Science
Chromatography is used for separating lots of mixtures, not just colours. For example, it can be used to determine the ingredients that make up a particular flavour or scent.
What is white light? White light is made up of all the different colours mixed together. White light comes from the sun and from white lightglobes. You can sometimes see the colours of white light when it passes through something like a prism or when you see a rainbow.
Why does mixing many colours make black? Colours in ink and paint are visible to us because they absorb some colours in white light and reflect others. The reflected colour is what we see. For example, green ink looks green because it reflects the green part of white light and absorbs all the other colours. When you mix green, red, blue, and yellow ink, each colour takes away some light – they take away so much light that very little light can bounce back to our eyes. That's why it looks black, because black is what we see when there isn't much light coming to our eyes.
Have you enjoyed learning about colour, light, and science? Keep exploring these themes at I Wish... in regional SA in term 3 2024.
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