Weather 2. More color fun.

I love the 'Rainbow Milk' experiment. The effects are immediate and fascinating, plus it is an ever-changing kaleidoscope.

simple ingredients for a complex effect

All you need is milk - we made this a variable by trying whole, 2% and skim -,  Dawn dish detergent (an essential part of every science cupboard), food color and a Q tip. I used the three primary food colors (R, B and Y), to get the best variety of hues.

Pour the milk into a shallow dish and add a drop of each food color at the edge, each one being spaced at about 1/3 of the circumference. Dip a plain Q tip into the middle of the dish, is there any effect? Nope. Now have the kids put a drop of dawn on the Q tip and repeat - WOW!!!! The spots of color vanish and as you hold the Qtip in place, they reappear, swirling up from beneath and mixing to make all the secondary colors and more. Watching the dish is so rewarding as every few seconds another eddy of color pops up and twirls. After 10 seconds the Q tip is removed but the effects just keep going all lesson long!

soon after removing the Q tip

10 minutes later

At this point it is hard to start anything else, so, keeping the dish in the middle of the table, I got the children to make a 'color spinner' from a paper plate and markers. The children ask a lot of questions about the effects we are seeing in the milk. "What happens if you leave the Q tip in?", What if you swirl the milk up yourself?", "Where do the colors go when you put the Dawn in?", "Why?" The Dawn detergent breaks the surface tension of the milk molecules, which is the only thing holding the colors at the edge of the dish. The fat molecules in the milk (whole milk works best here) start to move around, pushing the color molecules every which way and producing the marvelous effects we see here.

The plate coloring for the spinners is encouraged to be 'scribble scrabble' - you would be amazed at how a lot of children cannot bring themselves to do that! Anyway, I put a toothpick in the middle of the finished plates and showed the children how to spin them - the original design and colors are blurred and often appear completely different as the pictures go past our eyes too fast to register on the brain. Once they got the knack of spinning the children were really enthusiastic - and impressed that the messier the plate, the better the effect!

making the color spinners

 

A really popular class lesson that takes on a life of its own!