We’ve found a brilliant art-science activity to share! If you have young kids, you’ve probably come across the milk-soap-food colouring experiment which did the rounds on Facebook and Pinterest a while ago. I know both my girls have seen this experiment at kindergarten so we’ve never bothered doing it at home…until now. Last week, I chanced across a couple of videos (see a great example here) where artists have taken this simple idea to another level, and we were dying to see if we could achieve similar results ourselves! So we’ve been swishing paint around milk for a couple of days and made our own video! Hope you like it.
It requires just a few basic household supplies and ideally, a good range of paint colours to create these vibrant, swirling works of art.
We had such fun making these. There was a lot of oohing and aahing as the colours flowed gorgeously around the tray; a mesmerizing illustration of fluid dynamics. Dropping the paint into the oil created juicy baubles of colour which we added to the swirling mix and the girls were completely fascinated by the different ways in which the liquids interacted with each other. I was amazed at how long this captured their attention.
If you fancy having a go with creating your own, here’s what you need:
Some tips for good results:
Use a large tray
Most instructions suggest using plastic disposable plates, which we also tried, but using something a little larger really gives the liquid more space to flow and makes the whole spectacle more dramatic. Obviously uses up more milk though!
Mix up a wide variety of strong colours
Prepare a good range of paints – and experiment a bit to get the paint density right – too watery and the colours will be weak, too thick and the paint will sink to the bottom of the tray.
Having a delectable array of colours makes this a lot more exciting than the standard experiment. Metallic colours are especially mesmerizing! We did try adding loose glitter, but found it doesn’t flow very beautifully.
Throw in lots of paint right from the start – not just a few drops as usually described in the standard experiment. The girls put generous amounts of colour on their milk prior to setting off the fluid movement with soap as you can see below!
Create oil-paint baubles by pipetting/ syringing paint straight into a small cup of oil. These can be added to the milk mixture to make little colourful “islands” for the colours to swirl around.
The girls also enjoyed blowing hemispherical bubbles over their art at the end. The soapy bubble solution sometimes set off another round of colour movement and the girls were intrigued by the ability to drop blobs of colour through the bubble without popping it.
We also tried spinning the trays on a turntable during the marbling process to see what would happen.
Here are a few clips of the processes…
There are a fair few scientific ideas in there to talk about, but at this age the girls were mostly just interested in playing with the luscious colours. The movement generated when the soap is added to the milk demonstrates the Marangoni Effect.
The Marangoni Effect says that fluid will want to flow from areas of lower surface tension to areas of higher surface tension. Soap has a lower surface tension than water or milk, so when soap is placed on the milk’s surface, it lowers the surface tension of the milk immediately around it – which then wants to flow away to areas of higher surface tension, until the surface tension is balanced all across the entire surface of the liquid. The paint simply makes it all visible. But I’ll admit it was not easy explaining surface tension to kids! Or the polarity of soap molecules. All good stuff for later though!
Apparently you can even make a print of your fluid art using watercolour paper laid across the surface for a few seconds. I couldn’t get the kids to stop playing long enough to make a print before the mixture turned too sludgy. But I reckon we’ll have another go at this soon. Both girls wanted to do it again today after school. But unsurprisingly…we’re out of milk.