Most anyone who has attempted a bath bomb can tell you what a disaster it can be. If you're making them for fun, it's just a womp womp. But if you're making them to sell, it can be a huge setback and eat at your profits for an entire quarter just wasting citric acid (not that I would know...).
To save YOUR time and money, here are some quick tips that you can nibble at so that you don't waste 10 lbs of citric acid before crafting a sellable batch.
1. Go Easy on the Oil
It's really easy to go overboard on oils (whether fragrance, or for moisture) because they don't immediately fizz on contact. This gives you false confidence that you are creating a solid bath bomb with great packability that won't crack or implode - key word: FALSE. A bath bomb overloaded on oils will expand in the mold, popping and fizzing, and making release impossible. If left unmolded to dry, they can crack even after 2 days of what seems like uneventful drying. They can also make the bath tub too slick, and make your skin feel slimy instead of pleasantly moisturized. I find that 2 tbsp oil per 2 cups baking soda and 1 cup citric acid is about the maximum oil my bombs can handle.
2. To Mold or Unmold?
This will vary greatly on the type of mold you use. I use aluminum and find that if I leave my bombs in the mold for more than an hour, they aren't coming out without a fight. However if you unmold after 15 minutes, they can appear to hold their shape and then crack overnight while you're minding your own business. The drying technique I currently use is one that I learned from Desert Cloud Soapworks in the following video: https://www.youtube.com/watch?v=IpD3J1W2TjU&t=419s
Long story short, you can leave HALF of the mold on for an hour, then switch to the other side, then immediately shrink wrap. They WILL still dry! This does mean that you will have to have multiple molds if you want them all to be the same size. So stock up!
3. Which Mold Type?
On that note, which mold is the best if your goal is harm reduction in bath bomb production? SHORT ANSWER: Aluminum. I do not recommend plastic unless you are planning to throw your bombs straight into the trash, OR if it is your ONLY batch of bath bombs and you are planning to GIFT them still inside the mold. I have personally never tried stainless steel, because I am not made of money. My first batch of bath bombs with the aluminum molds was a mess because I left them in over night, and ended up having to dent them horribly by banging them with a spoon to remove my rock hard molds. Boo!! However, I ended up going back and buying 2 more sets of those same aluminum molds once I had perfected my packing anf drying techniques.
4. Do I REALLY Have to Shrink Wrap?
If you're planning to sell or ship your bath bombs, probably yes. Some companies are going for the zero waste thing and attempting their bombs at shows without being wrapped. Good for them, but I have yet to see a display like this that isn't a crumbling mess. My own totes are a disaster area after packing and unpacking my shrink wrapped fizzies and carefully cushioning them with packaging. In my experience, bath bombs that are shrink wrapped are the easiest to handle, especially since you never know whose grubby fingered little one is going to grab an armful and run off down the hall before grandma can catch them (this does happen). You would THINK that since bath bombs need to be as dry as possible, that loosely wrapping them or even leaving them open would be beneficial. In my experience, loose wrapping (like a sandwich or cello bag) is worse than NO wrapping. Moisture loves to get trapped in there, and if the humidity is above 50% outside, just walking your tote into the building is going to have a great impact on their fizz and float ability. The good news is that as long as you read reviews, shrink wrap is pretty easy to work with, even if you only have a hair dryer. If in doubt about the size, GO BIGGER! They shrink!
There are 3490860934760437698 things that can go wrong with your bath bombs. You'll pull your hair out if you test everything yourself. Take it from the thousands of us who failed batches first.
If you have more concerns about bath bomb crafting, Soap Queen is a great resource on troubleshooting before you even begin:
Can you think of anything that wasn't covered here or in either of the 2 linked sources? How long did it take you to develop your tried and true bath bomb recipe? Leave a comment below! Happy fizzing.
P.S. The one GOOD thing about 10 failed batches of bath bombs is that it cured my nail fungus.