Sunday, May 15, 2016

Weekday Wonderings: Is guar gum a good thickener for bath bombs? What's the science behind bath bombs?

Wow! What a lovely outpouring of concern and help I've seen over the last few days. You've made amazing suggestions for how I can supplement my income and re-assured me that things happen for a reason. I totally believe they do, and I'm open to what can happen next. Please keep those ideas and thoughts coming!

The list of things I'd like to write about on the blog gets longer and longer every week, but I need to get to your comments and questions as Weekend and Weekday Wonderings! So let's get started!

In this post on bath bombs, Maria asks: I have a recipe for bath bombs using corn starch, when looking for it I found guar gum which someone said was better but I can't find any reference of it being used in bath bombs. It is a binding agent I can see but not sure how it would work?

I'm seeing a resurgence of interest in making bath bombs, which makes me happy as I love making them! They were the second project I made - the first being bath salts - and the one that lead me to the Dish forum, where I learned how much I loved cosmetic chemistry and lead me on this path as Swiftcraftymonkey! 

I make my bath bombs with four ingredients - baking soda, citric acid, oil, and fragrance oil. I don't use corn starch or cream of tartar or anything like that as I find that a 2:1 ratio of baking soda and citric acid held together with oils works best for me. As you'll notice, I don't use alcohol or witch hazel to keep them together: I prefer oils as they don't set off the fizz early and they offer some moisturizing in the tub. If you wanted, you could put some polysorbate 80 or PEG-40 hydrogenated castor oil or another solubilizer with the oils to make them emulsify better in the tub. 

Would guar gum be a good binder? No. Because it's a powder that will just behave as any other powder in the citric acid until it was activated with water. We don't want to add water to a bath bomb as it sets off the fizz, so the first time the guar gum should interact with water is when we add it to the tub. And we don't want it holding the bath bomb together in the tub as it should break apart and melt when added to the water.

You might be able to make a slurry of it and add it to a bath bomb, but that will set off the fizz. I honestly can't think of a good way to use guar gum in a bath bomb, but I'd love to hear how it might work if you're using it! 

Why do bath bombs fizz when added to the bath? Do you remember mixing baking soda and vinegar together and watching it fizz? That's called an acid-base reaction and the acid - vinegar - and baking soda - base - combined will release carbon dioxide gas, which is the fizz. When we make bath bombs, we're taking the baking soda (base) and citric acid (acid) and combining them without water. We need that water to start the reaction and make the fizz happen. That's why we want to store bath bombs in plastic wrap or other things to keep out water until we want to use them. 

As an aside, this is why people in really humid places - like southwestern B.C., where I live - might not be able to make bath bombs all year round. The water in the atmosphere can set off the fizz! I know this to be true as it happened to me the third time I made them! 

I was just reading why corn starch is added to the bath bomb. It's to divert any water to that ingredient instead of setting off the reaction in the baking soda and citric acid. It was suggested to use Epsom salts for that purpose as well. I don't know if it works that way, but it certainly is an interesting idea.

If you're curious about the molds, I bought those at Voyageur Soap & Candle a few weeks ago. I think they are 1.75 inch diamter molds. And the vibrant colour of the pink/red one is red lake from Windy Point Soap. I don't work for either of these companies - although I do teach at Voyageur - and receive nothing if you click on the links to look at or buy the products. (I think that's called an affiliate program, and I don't belong to any of those kinds of programs at all.) I'm leaving them in overnight to see how the bath bombs work out. They fell apart after an hour of waiting, and I understand that you're supposed to leave them for 24 to 48 hours, so I'll let you know how they worked later this week. And it's super humid here this week! 


Maria Seabrook said...

Thank you for looking into my question :)

I have tried using a combination of Oil and shea butter but I think my ratio was out as they were just too soft.. too much oil perhaps..

I ended up adding a load of epsom salts and making fizzy bath salts from that batch :)

Elyse Duffy said...

I want to make bath bombs but instead of oil I want to use a surfactant like coco glucoside. Considering coco glucoside is about 50% water will I need to preserve the bath bombs?

Susan Barclay-Nichols said...

Hi Elyse! Check out this post on the topic.