I came across this recipe for making homemade watercolors. It seemed like a fun art project for the kids to both make then use. Luckily, we had all of the supplies on hand, and even an empty plastic egg carton (though in the future I would buy little individual toss away tupperware with lids.)
Watching the vinegar and baking soda mix.
Each of the girls picked an individual color to make, then with the leftover mix I made a few other colors.
The paint we mixed in the small tupperware containers and left uncovered became very dry. It was difficult to use and the children were sort of frustrated with it. The colors we mixed and kept covered in the egg carton remained somewhat runny after 2 days. The colors were bright and vibrant.