All it takes to make this delicately scented DIY is a little mixing, some gradual spritzing, and a few minutes of molding. When you're finished you'll have dozens of effervescent Muffin Tin Bath Fizzies in a variety of shapes and colors that will scent and soften bath water as they bubble. Stuff stockings with cellophane bags filled with stacks of the colorful blocks. They make great gifts for everyone on your list, no matter their age. Experiment with colors and scents; mix yellow and red to make orange, for example, and try blending lemon with lavender.
Sift 1 3/4 cup baking soda, 1 cup citric acid, and 2 cups cornstarch through a sieve to remove chunks. To make different tints, fill small spritzer bottles with water and add about 6 drops of food coloring to each.
Pour 1 cup of powdered mixture into a glass bowl. Lightly spritz, stirring after each spritz, until powder is desired color. Add water slowly, so the mixture does not fizz. If mixing two tints, alternate colors as you spritz. Check the consistency of the powder with your fingers; when it can be tightly packed or shaped, stop spritzing—this may take a little while.
Select an essential oil. Add 5 drops if it's one of the stronger scents—like peppermint or lavender—6 if it's a weaker one—like lemon or grapefruit. Mix it well before firmly packing the mixture into small baking molds. We used 1/4 cup for each fizzy, which is good for one bath. Allow mixture to set for two hours, then pop out carefully. Repeat with different tints for remaining powder.