Today we’re creating some striking bath bombs to celebrate the winter solstice (technically the solstice was the night of the 21st, but here in Calgary the 23rd is only 8 seconds longer than the 21st, so I think we can still call it solstice season!). A cool, purpley base shimmers like the night sky with accents of colour-shifting biodegradable glitter. Once in the bath, these sparkly tub treats fizz away, turning your bath water purple with dancing whorls of glitter. Pair with a mug of hot tea and a good book for a perfect winter night!

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My bath-bomb-making has definitely evolved over the years. If we go back and look at the first-ever bath bombs I shared on Humblebee & Me, they were ok. They fizzed when dropped into a tub, and that had me pretty stoked back in 2011. I slowly tweaked and improved my formulation and process until I decided I wanted to make hand-moulded spherical bath bombs. That threw a wrench in things because it turns out spherical bath bombs are much more finicky—the mix + technique has to be just right or they won’t mould properly. So, I spent a couple of days making dozens and dozens of bath bombs before I felt I had that more or less sorted, and I’ve been carrying on from there ever since. I’d had a chat with Michele at Windy Point about her experience with presses and bath bombs that had me thinking there’d be another learning curve when I graduated to a press… and I was right.

The water soluble dye.

When I first set to making bath bombs with my press I tried a batch the way I’ve made bath bombs in the past—mixing up the dry ingredients, blending in the oils, and then gradually misting in just enough witch hazel and 70% isopropyl alcohol to mould the bath bombs without them reacting prematurely. It worked decently enough, but it clearly wasn’t ideal. It just wasn’t as streamlined as I felt this sort of thing could (and should) be—so I turned to YouTube and binged on Ariane’s bath bomb making videos. I learned a few things from watching her work her magic. Thing #1: she adds the wet things to the baking soda and gets that all blended in before adding the acidic ingredients—meaning there’s no chance of the mixture reacting because only half of the reaction is present. Amazing. No more frantic mixing and misting! Thing #2: the mould is typically packed a lot more before pressing than I would if doing a hand-moulded sphere. Thing #3: The bath bombs are pretty dang sturdy (when done right) when they come out of the mould. Thanks, Ariane!

So, I shifted the order I mix things up in and re-worked my formulation to include the witch hazel right from the get-go rather than it being an “as needed” thing in a mister bottle at the end. I’ve found this gives much more predictable results, and using witch hazel instead of a blend of witch hazel and 70% isopropyl alcohol means I don’t typically have to re-wet the mixture while I work (provided I’m only doing about ten bath bombs in one go). It’s also just SO MUCH NICER. The spritzing and mixing aren’t horribly fussy, but still a lot fussier than this new-to-me process is. The cube mould is much more forgiving than the spherical mould for the Bath Bomb Press, so it was a good place to start off my pressed bath bomb learning curve.

I’m also working with new water-soluble dyes from YellowBee—these beautiful dyes create bath bombs that dye your bath water! I’ve been making lots of things with these stunning dyes all summer/fall/winter long and hoooooo boy are they strong. I made some bar cleansers that leave the side of the tub pink and dye my bath water (that wasn’t my intention, but cool!)—and that was at 0.05%! So, knowing I wanted to make some bath bombs that would transform my bath water into colourful people soup, I started there, and ended up going even lower and still finding the bath bombs dyed the water and were very colourful. These dyes are so dang cool!

For these bath bombs, I used a dye called Acid Black 2. It is actually a super, super dark cool purple/dusty lavender colour, so at lower concentrations, you get more of a purple than a black. I tried two different concentrations: 0.03% dye gives a dusty purple bath bomb that’ll dye your bath water without leaving a ring. Using 0.2% dye creates a much deeper purpley-black bath bomb that dyes your bath water an even deeper shade of eggplant, but that does leave a ring in the tub (I’ve found even concentrations as low as 0.05% can leave bathtub rings, so it’s not at all surprising that 0.2% does). I’ll leave the concentration choice up to you—if you don’t mind a bit of tub scrubbing and like a darker bath bomb, use more dye. If that’s not your jam, use less dye. Please read the substitutions list for information on how to adjust the formulation for more dye.

This is the level of purple you’ll get from 0.03% dye.

For decoration, I knew I’d need to involve some silvery biodegradable glitter to channel the stars and moon on a dark winter night. I ended up trying two different options, and I love them both! Option one is a glittery mica/glitter drizzle/splatter. It’s abstract and ultra-shimmery once it dries—it almost looks like chrome. Option two is a dusting of glitter on the finished bath bombs for a bit of a “stars in the night sky” look. Both are lovely, so do whichever strikes your fancy!

The finished bath bombs are lovely—fizzy nuggets of bath-boosting joy. Enjoy watching your bath water slowly turn purple as the bath bomb dances around the tub, dispensing glitter and bubbles. Whee!

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Winter Solstice Bath Bombs

4.16g | 0.52% witch hazel
0.24g | 0.03% black water soluble dye

424g | 53% baking soda (USA / Canada)
76.8g | 9.6%  Epsom salt (USA / Canada)

216g | 27% citric acid (USA / Canada)
40g | 5% Cream of Tartar

12.8g | 1.6% Polysorbate 80 (USA / Canada)
20g | 2.5% apricot kernel oil (USA / Canada)
6g | 0.75% fragrance or essential oil (see substitutions list below for details)

To decorate
Silver-white biodegradable glitter or mica, as needed
Colour-shifting silver-white biodegradable glitter or mica, as needed (optional)
99% isopropyl alcohol or isododecane, as needed

Weigh the witch hazel and dye into a small dish and whisk to combine/bloom.

Weigh the baking soda and Epsom salts into a large bowl. Stir to combine, and then add the dye/witch hazel mixture. Put on a pair of disposable nitrile or latex gloves and blend the mixture thoroughly.

Up next, weigh in the citric acid and cream of tartar, and blend that into the mixture as well. Last up is the Polysorbate 80, apricot kernel oil, and fragrance. Weigh those into the bowl and blend thoroughly with your gloved hands. When you’re done you should have a clumpy mixture that holds together well when squeezed firmly.

Now it’s time to mould the bath bombs! You can hand-mould these, as described in this post/demonstrated in the partner video, but I opted to press these bath bombs with my beautiful new Bath Bomb Press and the 1.75″ cube mould. I set the press to ~45psi and pressed 75g of the mixture for each bath bomb. Be sure to watch the video to see this in action! The mould can hold 100g (3.5oz) of bath bomb mix and I’ve done that, too—it requires a bit more fussing and pre-packing to get it all to fit enough to press it, but the end result is much more cube-like. 

Once the bath bombs have been moulded we can decorate them and leave ’em to dry! I played with two different decorating options:

For a drizzle/splatter/chrome effect: Mix up the glitters/micas with enough 99% isopropyl alcohol to make a liquidy slurry, and then use a disposable pipette to suck up some of the shimmery slurry and drizzle/spray it over your bath bombs. I find the glitters tend to settle fairly quickly, so make sure you’re stirring the mixture as needed.

For a sparkly night sky/glitter effect: Mist the surface of the bath bombs with some 99% isopropyl alcohol to give the surface of the bath bombs a bit of grip, and then dust with glitter. The glitters from YellowBee come in little plastic squeeze bottles with a sort-of glue bottle dispenser top, so it’s really easy to dispense little poufs of glitter over the bath bombs with ’em.

When you’ve thoroughly glittered up the bath bombs to your taste, leave ’em to dry for 12–24 hours before packaging, using, or gifting. Enjoy!

Substitutions

As always, be aware that making substitutions will change the final product. While these swaps won’t break the recipe, you will get a different final product than I did.

• As I’ve provided this recipe in percentages as well as grams you can easily calculate it to any size using a simple spreadsheet as I’ve explained in this post. As written in grams this recipe will make 800g. The number of bath bombs this makes is entirely dependent on the size of your mould. I made ten 75g bath bombs with a bit of leftover mix to spare (technically there was 50g of mix left but bath bomb making is somewhat messy and it definitely wasn’t all in the bowl once the first ten were done).
• To learn more about the ingredients used in this recipe, including why they’re included and what you can substitute them with, please visit the Humblebee & Me Encyclopedia. It doesn’t have everything in it yet, but there’s lots of good information there! If I have not given a specific substitution suggestion in this list please look up the ingredient in the encyclopedia before asking.
• Don’t substitute the baking soda or citric acid.
• You don’t have to use the dye if you don’t want to; replace it with more witch hazel if you don’t want colourful bath bombs.
• If you do want colourful bath bombs, but you don’t have a water-soluble dye, replace the dye with more witch hazel and then swap out 0.5% Epsom salts for a mica of choice.
• To use more water soluble dye (read the pre-amble for details):
  • Increase the dye to 0.2%
  • Increase the witch hazel to 0.75%
  • Drop the Polysorbate 80 to 1.5% and the apricot kernel oil to 2.3%
• You could try a different salt in place of Epsom salts.
• You can try replacing the Cream of Tartar with more citric acid, but the Cream of Tartar makes the bath bombs much harder and easier to mould.
• Give this a read for Polysorbate 80 alternatives.
• You can substitute the apricot kernel oil for another lightweight, inexpensive liquid oil like sweet almond, grapeseed, or sunflower seed.
• The fragrance is up to you. You could use a bath-safe essential oil instead, or any fragrance oil you like. I used Salty Sea Air and Ocean Mist in different batches as they smell cool and fresh—much like the air in the depths of winter!
• The glitter topping is optional, but pretty!