These ornaments are so much more than the sum of their parts: A flash of holiday alchemy transforms inexpensive glass globes and a few dropperfuls of paint into marbled masterpieces, and the guests at your ornament party will have a ball making them.
Experiment with dribbling paint down the sides or squirting it right into the bottom and tipping the ball upside down over a cup. (Most designs look great, but if a child is really unhappy with his or her ball, you can swirl the inside of the ornament with hot water and start over.)
Remove the tops from the ornaments (a parent's job). You may want to inspect the tops of the ornaments for stray glass threads and smooth them with the side of a toothpick.
Pour the paint into the cups, one color per cup, and stir a little water into each until it reaches the consistency of heavy cream. Put an eyedropper in each cup.
To decorate a ball, squirt a few drops of paint into it and swirl before adding another color.
Dry the balls upside down, perched on paper cups, and replace the tops when they're dry.