The homemade bath bombs we made for Mother’s Day last year were such a hit with both my kids. They loved every step – from mixing and molding the fizzies to delivering them. So I came up with these Valentine’s Day-inspired homemade bath bombs that reveal a secret message when placed in the bath!
Of course, we had to test a few bath bombs first. And now that my 5 year-old has seen just how the hidden messages float out from the fizzy eruption, she can barely wait to surprise her friends with her own Valentine’s Day homemade bath bombs. For more creative and fun science, check out our 30 Science Experiments in our shop!
To make 6 large heart-shaped bath bombs, we first gathered a few supplies:
- 1 cup of baking soda
- 3/4 cup of corn starch
- 1/4 cup of Epsom salt or cane sugar
- 1/2 cup of citric acid (available in natural food stores or online for canning)
- Food coloring (optional)
- Essential oils (we used rose, lavender and jasmine)
- Jojoba or almond oil (optional, but leaves skin soft)
- Large bowl
- Measuring cups (not pictured)
- Spray bottle
- Silicone heart-shaped muffin mold (pictured below)
For the messages, we needed:
- Colored foam sheets (available at the dollar store or craft stores)
- Fine line permanent marker
Making the Messages
To make the hidden messages, I made a template by folding a piece of cardstock in half and cutting a heart shape to fit in my muffin mold. I just eye-balled the size of the heart, making sure it was small enough to fit nicely in the muffin mold but big enough to allow my 5 year-old to write her message on. Once I had a template, I had A use it to trace the shape onto a piece of colored foam. We were making 18 bath bombs, so I had her trace 20 hearts in case we needed an extra or two.
After A cut out all the foam hearts, she turned her attention to choosing just the right message for each friend and carefully writing it on a foam heart with permanent marker. You want to make sure your marker is waterproof as it will get wet.
Homemade Bath Bombs
Next came the fun part: mixing up the homemade bath bombs! As I read off the ingredients, A excitedly gathered all the supplies and got right to work. First, she measured out the baking soda, cornstarch, Epsom salt and citric acid and mixed them in a large bowl. This recipe is pretty forgiving and makes a perfect measuring activity for young kids.
I asked A what scent we should make for our first batch and she chose rose. While she measured and mixed the dry ingredients, I filled the spray bottle with about 1/4 cup of water, several drops of rose essential oil and a squirt of pink gel food coloring. I handed A the bottle and asked her to spray a few squirts at a time into the bowl, stopping to whisk the mixture. A loved watching the mixture fizz each time she sprayed it.
It’s pretty important to lightly spray the mixture, wetting it enough that the mixture forms a clump when squeezed but not so much that it continues fizzing. Go slow, spraying only a few sprays then testing it with a squeeze.
Once our mixture clumped, A add a tablespoon or so of jojoba oil and wicked the mixture thoroughly. Since we were making gifts, we used jojoba oil instead of almond oil in case some of A’s friends had a nut allergy we were unaware of.
If you add too much water, the citric acid will continue fizzing and the mixture puff up in your mold. If you notice this happening, you could try to salvage the mix by adding more baking powder and/or cornstarch a tablespoon at a time to help absorb some of the extra water.
Now A was ready to add the homemade bath bomb mixture to the heart-shaped muffin mold. She used a tablespoon to scoop a little of the mixture into the bottom of each mold, filling it about half way.
Next, she pressed the mixture down and added more until the compressed mix filled about half the heart.
She placed one foam heart message in each mold and covered the message with more mixture.
Then, she pressed the mixture firmly down with her hands. She repeated adding mixture and pressing down until each fizzy couldn’t be compressed any more.
We left the homemade bath bombs to dry over night then carefully popped them out in the morning to further dry. I did notice on the first batch that the fizzy cracked a little where the message was. I fixed this by making the next messages a wee bit smaller allowing there to be more area where the top and bottom layer of the fizzy joins.
Once they were completely dry, we packaged them up to await V-day and headed back to the kitchen to make the next batches: lavender and jasmine.
This Valentine’s kid’s science activity combined a few of my kids favorite things: fizzing, mystery and little mess making. It also makes for a super cute but easy kid-made Valentine that any kid (and some grown-ups too!) would love to receive.
The Science Behind It
When you drop your heart bath bomb into the tub, the water sets off a chemical reaction between the citric acid and the baking soda (sodium bicarbonate). That’s why the dry mixture fizzed when it was sprayed with water. When citric acid and baking soda react in the water, carbon dioxide gas is created, making those relaxing fizzing bubbles.
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