Ice-cube trays serve as molds, giving the fizzies their shape. Using a flexible silicone model lets you slide the cubes out smoothly without breaking them. Show off the colors of the bath fizzies in glass jars with screw tops, the kind used for storing sugar and flour. Pack each type of fizzy in a separate jar so the scents won't meld. Write the name of the scent on a vellum tag (choose a shade that matches the fizzies), and punch a hole in the top. Thread the tag with ribbon, and tie it around the jar. Citric acid, a common food additive, is available at wine-making-supply stores, some spice shops, and online. When citric acid is combined with baking soda and placed in water, a chemical reaction creates bubbles.
*Makes 1 dozen (Use 2 per bath).