OK...so it's not actually a science experiment. LOL. I suppose you could tie surface tension or something into it...but I digress.... it's more of just a messy cool kaleidoscope thing to do with your kids that they will love. It's sort of pointless...but it's really fun to watch. Heck, I did it with my husband...and he LOVED it. "Neato!" This is what you do.... Get a plate. Fill it with milk. Very carefully, WITHOUT stirring it up...drip several different colors of food color in the center of the plate....get the colors close together, or even overlap a bit. Now, take some dish soap...and coat a cotton swab. Stick the tip of the cotton swab in the center of the colors....and watch the party. If you want to get really adventurous...drip a whole drop of dish soap in there. Crazy! I wasn't even alive in the 60's....and this made me remember them! LOL...have fun and enjoy Playing 1960's music enhances the experience.
We've done that one a few times it has more to do with how the lipids in the milk react with the solvents from the soap rather than surface tension IIRC, but mostly just cool to see!
It's both, actually, (since the lipids gather on the surface, the spreading movement you're seeing is also a great visible demonstration of surface tension) but you're dead right that the lipid solvent reaction is likely the principle whoever thought it up was trying to illustrate. I just think it's pretty
