Bath bombs are so cool. Basically, you’re doing a chemistry experiment in the name of Spa Day. How could anyone not like that combo? They also make great gifts (hint! hint!) and kids love them. Since I started this Bath Bomb making experiment, my son has refused to take a bath without one.
Bath Bombs aren’t all that cool until they hit water, and then they start fizzing like crazy and create a fun, foaming bath experience as they dissolve. The reason for this is an acid-base reaction.
You know when you were a kid how you made volcanoes by pouring vinegar into baking soda and creating faux lava? Well, the same thing is happening with these bath bombs. Citric acid provides the acid component and baking soda provides the base. They don’t react until they get wet and then – ta da! – bath bomb fizz power galore.
The stuff that dissolves into the bath water makes for a nice, soothing bath. The citric acid and baking soda pH neutralize as they fizz, the cornstarch is soothing to dry skin and rashes, and the Epsom salt (pure Magnesium Sulfate) helps relax muscles and restore Magnesium levels in the body.
Combine these ingredients with a few drops of essential oil and some food coloring if you want to personalize your bath bombs. I like lavender and chamomile essential oil for a relaxing vibe and eucalyptus or lemongrass for something more awakening.
The Two Tricks to Making Bath Bombs.
Trick # 1: Getting the dry mix wet enough to be moldable without activating the acid-base reaction. I found that stirring the dry mix constantly with a whisk in one hand while dribbling in the water with the other hand worked the best. If any part of the dry mix starts to fizz up, just mix that area quickly until is stops. As soon as the dry mix holds together when you squeeze it tightly, stop adding water. Martha Stewart says you should get a spray bottle and spritz the dry mix, but that’s more fussy than I can handle.
Trick # 2: Molding the bath bombs. I tried a few options for molding these – silicone ice cube trays, portion scoops, etc. – and didn’t have the best luck. Nothing that deflected under pressure – like silicone – worked that well. I tried those plastic Easter egg shells (anyone with kids has these lying around) and was able to mold dome-shaped bath bombs that worked pretty well.
Then I thought – everyone has a muffin tin, so I should see how those work as molds. And then I remembered that I own a pan designed to make adorable mini-bug-shaped cakes. (I had an employee discount at Willimas-Sonoma and an impulse control problem a few years ago, what can I say?)
Bath Bombs turned into way more cool Bug Bath Bombs.
I was pleased to find that the bath bomb mix packed very well into the mini-bug cake pan, and, after a little practice, the molded bath bombs came out of the individual bug shapes pretty reliably. Winner!
Step-by-Step: DIY Really Cool Bath Bombs
The photos for this tutorial were taken over a few batches of bath bombs, so the color of the demo bath bombs will change.
Get Your Stuff
You’ll need citric acid, baking soda, Epsom salts and cornstarch.
You can get the citric acid in shops that cater to brewers or cheesemakers or in the canning section of very well stocked supermarkets. You can also order it online. This is what I use. If you want to color and scent your bath bombs, you will need food coloring and essential oils.
If you have an objection to corn starch, I tried a batch with half corn starch and half potato starch and, while it seemed to require more water to stick together, it worked. So play around.
You’ll also need something for molding your bath bombs. My mini-bug cake pan turned out cool bath bombs, but use that as an inspirational starting place. Look around your house and I bet you have a great bath bomb mold kicking around too. This is the specific pan I used.
Make the Bath Bomb Base
In a large bowl, mix together the citric acid, baking soda, cornstarch and Epsom salts.
With one hand, stir dry mix constantly with a whisk. With other, drizzle in the water until the mixture just clumps together. If you start to see or hear fizzing, that means there is too much water in one area and you should stir that area quickly to distribute out the moisture.
Add just enough water so that the mix holds together when you squeeze it in your hands.
If coloring your bath bombs, use a few drops of food coloring to achieve the desired shade. I used paste gel food coloring which is very concentrated and only needed a small squeeze to get the shades I wanted. Knead well to distribute color.
If scenting your bath bombs, add in the essential oil a drop or two at a time until the your desired scent is achieved. Knead well to distribute scent.
My favorite scent/color combo of the batches I made was lemongrass in a pale yellow-green color. It turned out really delicious smelling! I also made a violet-tinted batch scented with chamomile and lavender. I’m hoping it soothes my son who hates to sleep before bed.
You want to be careful which essential oils you choose – ones with skin soothing properties are desirable. Though I have not personally experienced this, too much lemon essential oil can apparently make a bath a bit more astringent on the sensitive bits than anyone really wants. Always be considerate of the sensitive bits, people!
Pack Your Mold with the Bath Bomb Mix
Really get in there and pack it in. You want the mix to be very firmly compressed in the molds.
Smooth the tops of the bath bombs – if they are uneven on the bottom when you flip them over to unmold them, they tend to crack more.
Unmold Your Really Cool Bath Bombs
For the pan-type bath bomb mold I was using, I found unmolding was easiest if I set a sheetpan bottom-side-up on the bath bomb mold. Then, holding sheetpan and bath bomb mold tightly together, I flipped both over together.
The result was the sheetpan right-side-up topped with the upside down bath bomb mold. To finish unmolding I slowly – and very carefully – lifted the pan straight up off the bath bombs, which conveniently stayed behind on the sheetpan.
You do have to be quite steady-handed unmolding because the bath bomb mix is very soft at this point and if you bump it you will mess up the shape. Since the fun shape of these molds is what makes them, I didn’t want sloppy edges.
If you do mess up unmolding a bath bomb – or a whole batch – you can just smoosh the bath bomb mix right back into your mold and try again. If it starts to get too dry to work with, just sprinkle with a few more drops of water and mix well.
Dry Bath Bombs
Let bath bombs dry overnight.
In the morning a few of my buggies had minor superficial cracks and one of the bees had cracked its wing right off but they mostly stayed together. The ladybug – the simplest of the shapes – was 100% reliable. The more complicated designs had more problems in unmolding and with cracking.
Some other online instructions for bath bombs suggest letting the bath bombs dry in the mold, and that may be an option too – I needed to use my cake pan to make more bath bombs so I had to move a bit faster than that would allow. Letting them dry after unmolding worked fine. If you have experience with the “dry in the mold” method, please chime in in the comments.
Package As Desired
When bath bombs are fully dry, carefully package for gift giving or your own personal spa day. I placed six in assorted colors and shapes in a box lined with wood shreds. Shredded crinkle cut paper would also be good. I wouldn’t stack these for gifting – no mason jar filled with bug bath bombs, I’m afraid – they aren’t meant to be knocked around.
Printable Bath Bomb Instructions
DIY Really Cool Bath Bombs
- 1 cup citric acid
- 2 cup baking soda
- 1-1/2 cup cornstarch
- 1/2 cup epsom salts
- 2-4 tablespoons water
- Small squeeze of food coloring (Optional)
- 10 drops essential oil, or more as desired (Optional)
- Equipment: suitable mold for bath bombs
- In a large bowl, mix together the citric acid, baking soda, cornstarch and Epsom salts.
- With one hand, stir dry mix constantly with a whisk. With other, drizzle in the water until the mixture just clumps together. If you start to see fizzing, that means there is too much water in one area and you should stir that area quickly to distribute out the moisture.
- Add just enough water so that the mix holds together when you squeeze it in your hands.
- If coloring your bath bombs, use a few drops of food coloring to achieve the desired shade.
- If scenting your bath bombs, add in the essential oil a drop or two at a time to achieve the desired smell.
- Pack bath bomb mix into molds very firmly and smooth the surface of each bath bomb.
- Unmold bath bombs onto a sheetpan or other flat, dry surface.
- Let bath bombs dry overnight.
- Carefully package as desired for gift giving or your own personal spa day.
(These are affiliate links. Purchases made through these links cost you nothing extra but allow me to periodically enjoy a nice glass of wine while taking a soothing bath after way overdoing the weeding. Full financial disclosure here. Thanks for your support, folks. It puts the fizz in my bathwater.)
Citric Acid – We buy this stuff in 5 or 10 pound bulk bags because it gets used in canning, cheesemaking, dry baking mixes, happy-hippie weed spray and more around here. It’s quite useful stuff. Here’s a one-pound option.
Cute Bug Cake Pan – You can also use this pan to make cakes (but be honest – will you?) and it’s adorable. A substantially less expensive silicone version is also available, but I wasn’t thrilled with trying to firmly pack the bath bomb mix into squishy silicone molds. Proceed with caution.
Gel Food Coloring – This is great stuff. If you’ve only ever used the crappy drippy food coloring from the grocery store, think about upgrading. And of course, if food coloring skeeves you out, just skip it.
Essential Oils – Apparently there is a big controversy about essential oils. If you have a brand you love and trust, go for it! For this use, the most important thing is that they smell nice, so I went down to the Yuppie Hippie market and smelled all the brands until I found the one I liked the most. It was the Simpler Botanicals brand. If you don’t have a trusted brand, I recommend an in-person reconnaissance to your local hippie health food coop.169