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Hi I'm Dan, the lead formulator here at ST! We wanted to not only share what makes our bath bombs great, but the whole process of how we hand make them here in Los Angeles.
A basic bath bomb mix starts with sodium bicarbonate & citric acid. These 2 ingredients will create the fizzing reaction of the bath bomb, and the most common ratio is 2:1 sodium bicarbonate : citric acid. Changing this ratio can effect the fizzing speed. Our ratio is usually about 5:3 as it works best with our other ingredients.
Because we use high amount of oils in our liquid mix, we need binding agents & surfactants. A binding agent helps draw ingredients together that don't want to form a cohesive compound. A surfactant lowers the surface tension between 2 liquids, which helps our oils disperse & the foaming of our bath bombs in the water.
Xanthan Gum is a natural cosmetic grade binder & thickener. Most bath bombs use corn starch as their binding agent making up 7 - 15% of the bath bomb because it's the cheapest ingredient in the bath bomb. Our bath bombs are only comprised of about 1% Xanthan Gum, allowing us to increase the premium ingredients that matter for your skin 😘
Surfactants are needed in soap products so it's almost impossible to be sulfate free. Sulfates get a bad reputation because of SLS which is the cheapest form used in most soap products. SLS has a small molecular structure, so it can penetrate the epidermis causing irritation for sensitive skin types. SCS on the other hand has a larger more complex molecular structure and has been found to been found to be much gentler on skin. Here's a great article with more details: SCS VS SLS
Epsom salt is a great bath ingredient that people have used for decades, so of course we include it in our bath bombs. Once all these ingredients are added together we put them into a mixer to blend evenly & then move on to the liquids 👍
Taking out the corn starch was the key to allowing our liquid mix to be a true superstar. We maximize the amount of liquid mix we can put in every bath bomb & our liquid mix is truly remarkable & will leave your skin feeling amazing 😍
We use a special 5 blend mix of grape seed oil, sweet almond oil, sunflower oil, olive oil, and shea butter. This blend is premixed with a small amount of witch hazel extract & polysorbate 80. We explain in detail the benefits of every ingredient HERE
Polysorbate 80 is a high cosmetic grade emulsifier. We use it as a dispersing agent for mixing the oils into our bath bombs. It also helps the bath bomb color disperse in the water & not stick to your tub to help prevent stains. This high grade actually has skin benefits as well such as having a soothing effect on your skin 🙂
We only work with luxury fragrance houses spend months to create a unique fragrance specifically for ST.
The same goes for our colors. We source from professionals that use the highest standards of food grade safe colorants blended with glycerine which is a great ingredient for skin & keeps your bathtub from staining. Here is our goto partner for our colors: French Color
After the liquid mix & solid mix have been separately mixed/blended, we add the liquid mix to the solid mix in our mixer. For small batches, these can be hand mixed in a bowl, but we use mixers for 25 - 100lb batches.
It's important to fully blend the mixes together to avoid spotting. Minute time varies based on based on batch size. The last ingredient we'll add is isopropyl alcohol & mix for another 2 minutes. The alcohol makes the bath bomb mix wet & ready to be compressed, and will later evaporate out of the bath bomb. The amount added will vary based on the temperature & humidity in the air, but we usually use about 10ml/lb of bath bomb mix.
Bath bombs can be hand pressed, but to crank out 1000s a day we use air compressors with molds. We'll hand scoop 4oz of bath bomb mix, add your beautiful surprise ring, and then another 4oz of bath bomb mix before compressing.
Especially with the amount of liquids we use in our premium bath bombs, it's crucial to get all water moisture out of the bath bombs. We built a dehumidifying room that keeps the humidity under 20% & temperature above 30C. This helps minimize water moisture getting into the bath bomb which can cause the bath bombs to expand and get soft.
The best bath bombs deserve to have the best packaging! We use plastic wrap & heat to seal, before placing them into their own adorable box designed by our in house designers.
Some bath bombs get extra visual treatments such a sprayed on design, drip, or biodegradable glitter topping. Our sprays & drips are made by mixing Mica with a little bit of alcohol.
That's our goal! We love our formula that we worked years on, but we are continuously testing minor tweaks. We also do minor adjustments with speeds like our vampire bath bomb that bleeds out the red inside before the white outside dissolves.
And remember, these bath bombs are all hand made. The smallest mistake or issue with drying can cause a bath bomb to not be perfect. If you ever get a bath bomb that is soft or sinks, it's usually because of moisture. We'll always replace any bath bombs with issues if you just reach out to our team on Facebook Messenger!