To start, divide rice into one-cup increments and place into zipping storage bags. I made five colors, which was as much old rice as I had. Find enough small bowls to create the colors for each bag of rice, and pour 1-2 tablespoons of vinegar into each. Next, add a generous amount of food coloring. Your color will be richer if you add more – about 10 drops or so each.
Now, pour the food coloring mixtures into each bag, seal them tightly and have the kids squish the rice around so it is thoroughly coated with coloring.
Lay wax paper on a cookie sheet, and then spread the wet rice out to air dry. If your kids are impatient like mine, you can use a hair dryer to speed things up.
Once the rice is dry, get each kid two bowls and a spoon, divide the rice, and let them sort to their heart’s content. Mine have played with the rice several times, and it’s already gotten many hours of use. The only problem is the cleanup afterward. You might as well resign yourself to sweeping it up and tossing it, because it’s impossible to get it all back together.