Tools and Materials
Computer
Secret messages template
Igage waterproof paper
Scissors
Large bowl
Baking soda
Citric acid
Essential oil
Food coloring
Whisk
Spice or coffee grinder
Water
Small spray bottle
Ball mold
Kitchen towel
Plastic wrap or plastic bags
Bath oil (or any light oil), optional
Bath salt, optional
Bath Fizzies How-To
1. Use your computer to download template and print secret messages on waterproof paper. This floatable paper is ink-jet and laser-printable, it uses most inks, and inks won't run on this paper. Cut out message and roll it up.
2. In a large bowl, combine 1 cup of baking soda and 1/2 teaspoon essential oil.
3. In a spice or coffee grinder, grind 1/2 cup citric acid, 1/4 cup bath salt, and 2 drops food coloring. Grind to a fine powder, and add to the mixture in the large bowl. Begin whisking together thoroughly.
4. To mixture, add a couple of sprays of water. It should reach a crumbly consistency.
5. Fill each half of a ball mold.
6. Add message to one half of ball.
7. Using hands, pack mixture in, slightly overloading. Press mold halves together. Let sit several minutes; unmold.
8. To dry the fizzies, place them on a kitchen towel and gently wrap with towel to dry for 24 hours. Wrap or package fizzies in plastic to protect them from moisture.
Resources
Weather-proof paper from igage.com. Large, round stainless-steel bath fizzies molds from New York Cake and Baking Supply. Small, round (60 millimeter) plastic bath fizzies molds from Costal Scents. Large and small heart-shaped bath fizzies molds, citric acid, and essential oils from Majestic Mountain Sage. 2-ounce Mister Spray bottles from the Container Store.

Clarification please: Martha says let dry in mold, instructions say place on kitchen towel, wrap gently and let dry over night?
This is going to be fun. I like the idea of confetti too.
I'm going to use some silicone heart mini cupcake molds I found at a dollar store. They seem like the perfect size, and the dried fizzies should pop out of there pretty easily.
these r so cute but i dont have such round molds what else can i use to make such fizzies
I used mini heart-shaped cookie cutters and they worked great! First I very lightly coated the inside of the cookie cutters by spraying some cooking spray onto a paper towel and rubbing it on the inside edge of the cookie cutters. The fizzies set up in about 10 minutes, after which I was able to gently pry them from the cookie cutter. They rounded out a bit overnight, but maintained their shaper quite nicely. I also stuffed them with red heart confetti for added fun.
soap making supply shops have citric acid
try wine making stores
I found it at a small health food store in Chicago. It's a white powder. You could try Whole Foods.
where do you buy citric acid? i can't seem to find it anywhere!