I gave the girls a dish of 2% and a dish of heavy whipping cream. We proceeded with the experiment as we had before placing drops of food coloring in the milk. We noticed immediately that the food coloring in the 2% (top) spread more while in the whipping cream (bottom) it stayed put.
We dipped our toothpicks in dish soap and touched our colors. The 2% went wild while the whipping cream was much slower. We continued playing with the color until it was all spread. Really you could hardly get the 2% to react a second time, but it took a lot of time to spread all the colors in the whipping cream!
Then we decided to try a mix of half whipping cream and half 2% milk. The results were fabulous! It worked perfectly; just like whole milk!
By using the various liquids the girls were able to see how the amount of fat really affects the movement of the color. The food coloring is water soluble, so it is held in droplets in the fattier milk. But when touched with the soap, which will bind to the fat, the water soluble food color is then able to move. Because of the high fat percentage in the whipping cream, the soap works much slower in the fatty whipping cream compared to the "whole" milk. And the low fat percentage in the 2% means you barely need any dish soap to break through the fat allowing the color to move.
Just like our first experience with this experiment, the girls continued playing, adding color and soap until we had a uniform green color before we dumped the milk. Magic Milk is always a fun experiment, and it was great to be able to expand on it even if it was a result of my unpreparedness!