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cameron's picture

Perhaps I am not the only one who could use a break from the religion-suffused bickering. Here, then, for something completely different, is a bath bomb recipe.

I've had trouble making bath bombs in the past because I live in a climate that tends to be humid; the fizzy acid-base reaction gets started too easily. So I asked my friend Jake, who studied chemical engineering, to fine-tune a bath bomb recipe. I haven't made these myself yet, but Jake has made them with excellent results.

I'm guessing that he's using parts by volume, not weight.

His instructions:

Ingredients
Citric acid granular
Sodium Bicarbonate 98% pure (but you can use baking soda).
Non-reactive starch...corn works
Non iodized salt...kosher salt works and seems to work better.
Non-reactive oils. I have started using infused sunflower oils
Distilled or Spring water (something non-chorinated/fluoridated)
Simple carbonates (You can use borax...but I prefer making magnesium carbonates).

Mix citric acid, bicarbonate, starch at ratio of 1 part citric acid, 2 parts bicarbonate, 1 part starch.
Pour into heap. Sprinkle top with salt (no more than 1/2 part). This will assist in preventing water from the air beginning the actions early.

Mix solution in jar: 13 parts oil, 3 parts water, 1 part carbonate (borax). Change out infused waters and oils with parts. So rose water counts as water, scented oils count as oils etc. Do NOT use sulphuric carbonates!

Put dry in bowl and add liquid till you achieve 13 parts solid to 1 part liquid (about). It should make a crumbly chunk when you grip it.

Put bathbomb in mold to set...something airtight, if possible. Then put in fridge (NOT in freezer; freezing water BAD).

Wait a few hours.

Take bath bomb out of mold, apply oil to hands and use oils to smooth bath bomb.

(To make bath men, shove bathbomb mixture into gingerbread man mold lying on plastic wrap...then pull plastic wrap around it.)

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Whoops, no, it's parts by weight.

cameron's picture

I just checked with Jake. He's referring to parts by weight.

That should make it really easy if you have a good scale, especially if you have one that does metric measurements.

-- Cam

Thanks!

mindymonster's picture

My kids love bath bombs! It never occured to me to make them! Thanks for the recipe!

Something I've been meaning t

cameron's picture

Something I've been meaning to try, by the way, is packing bath bomb material into small Day Of The Dead sugar skull molds: Goth Bombs! It might even be possible to decorate them somehow with colored salts.

-- Cam

Homeschooling Application

Susannah's picture

This would be an excellent chemistry experiment! Any other ideas for molds? I can't think of anything I have lying around that would suit.

molds

Lynn's picture

At the worst you could use an ice cube tray, I'd think. If you buy something any candy, soap or candle mold would work I'd think. You're right, excellent homeschool application!

Lynn Siprelle, Editor

One more thing...

cameron's picture

Jake doesn't mention this in his instructions, but my hunch is that the best way to apply the liquid is carefully, with a spray bottle, as you would for pie crust.

From what I've seen with less-than-satisfactory experiments with other recipes, the real trick here is water management. You want enough fluid to hold the stuff together, but not so much that significant amounts of the acid and base go into aqueous solution and start reacting with each other.

If you're using this stuff for learning about chemistry, you probably want to make sure you're using materials that aren't using the old Arrhenius definition of bases, or things are going to get very confusing. Here and here you can learn the difference between some definitions of acids and bases, and learn why baking soda is a base even though it doesn't have an OH- ion to release. You might also like the balanced equations of the reaction. And if you were wondering why anybody would call NaHCO3 "bicarbonate", well, that's a good question.

-- Cam

I love it!

Lynn's picture

If you do this, take a pic!

Lynn Siprelle, Editor

Ikea has marvelous little rub

cameron's picture

Ikea has marvelous little rubbery molds for fancy ice cubes, if any of you happen to go by there. And I picked up some heart-shaped molds at a local craft store for a song just after Valentine's Day.

Small dixie cups might make good disposable molds. I'd try muffin trays, too. Or just about anything with a depression could be worth trying, really -- unlike candlemaking, cleanup is not a big deal if some of the bath-bomb stuff gets stuck in the mold, because the stuff washes right out. (Fizz!)

-- Cam

You're welcome!

cameron's picture

You're welcome! If you make them, I hope you'll post here and let us know how it goes.

-- Cam

Great Idea!

Susannah's picture

Thanks!

Will do! -- Cam

cameron's picture

Will do!

-- Cam

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