Ferric f*cking ferrocyanide

Hold onto your hats, kiddos, this post is going to look an awful lot like a chemistry lesson… I had a bit of a disaster when testing out a new scent this week, & I thought you might enjoy seeing the hijinks that can occur when you don’t closely monitor your ingredients.

See these? Gorgeous, no? These are two mica blends that I whipped together as potential colorants for the upcoming August Limited Edition. I wanted something green & glittering & just a bit weird… that top one had me doing the happy dance of joy, it was so perfect.

Aaaand here’s what I found when I came back to check the test batches of soap.

Where’s my beautiful green, dammit?!

To answer that, let’s backtrack just a bit, & explore exactly what is mica… Mica is what makes my soaps & Slips sparkle, that fine shimmer that makes bars like Dead Leaves on the Dirty Ground & Sweet Cheeks shine. Mica itself is a mineral with a myraid of applications, & we use it in the bath & body industry to give our products a glittery finish. Coated with other minerals or colorants, it suddenly looks like really intense eyeshadow & makes for an amazing range of colors.

The bulk of my micas are soap-stable, meaning that I can add them to my products & not see any change in the perceived color. As I’ve found out the hard way, though, two colors in my collection are not soap stable, thanks to a pesky additive known as ferric ferrocyanide.

Perhaps more familiarly known as Prussian Blue, ferric ferrocyanide is an inorganic (i.e. synthetic), FDA-approved colorant, safe for external use. It gives an intense matte blue that’s wonderful for color blending, & it’s lovely in my Super Green & amethyst micas.

If I were using these gorgeous micas dry, I’d have nothing to worry about – the colors would stay true when brushed on the skin or, in theory, on the surface of a bar of soap. But I’m adding them into a lightly alkaline soap base, which changes the game entirely, setting the stage for a very small but very annoying chemical reaction.

Added to soap, that lovely Prussian Blue blue fades within minutes, morphing my bright green mica to a sickly yellow. Remember when I had to pull The Man in the Moon for a few months last year? Unbeknownst to me, my supplier had mis-picked my last order & instead of sending me the soap-stable lavender mica I’d been using, sent me their amethyst mica, which contains ferric ferrocyanide. Suddenly my lovely lavender & gold bars were fading to a miserable pinkish hue; it took me several months to figure out what had happened & find an alternate purple colorant. (Oh Ultramarine Violet Oxide, how I looove you!)

Meaning my funky Super Green & lovely amethyst micas will be forever gorgeous in the jar, but unmitigated failures in soap. Phooey.

So, it’s back to the drawing board for the August LE’s colorway, & I’m taping closed my jars of errant mica so I’m not tempted to use them again in soap.

Or maybe I’ll try my hand at eyeshadows…


About Hayley

I'm a trained pastry chef, DIY queen & mother with my heart in west England, my soul in Chicago, & my feet in south-central PA. Paintbox Soapworks was born out of my love for handicraft, beautiful fragrances & clean hands. I play around with colors & scents & soothe my insomnia by dreaming up new ideas. I pull heavily from music (Waits, White Stripes, Wilco), books (Tolkien, the avalanche of children's books in C's room) & my own fertile imagination.
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7 Responses to Ferric f*cking ferrocyanide

  1. therhoda says:

    Hubby is fussing in the back ground worried about your safety. he all thank god she was using a base and oh gods she didn’t smell almonds did she? So i am letting you know that you are scaring the more chemically reactives with just the idea of adding that to an acid in any way.

    Me, I am still pouting about missing out on your trial of body butters!

  2. Hayley says:

    Oh therhoda, I didn’t mean to panic your husband! Remind him that I was once a pastry chef, & regularly roasted cyanide-laced apricot & peach pits without killing anyone 🙂 In ferric ferrocyanide, the cyanide is tightly bonded to the iron, so there’s little risk of anything nasty even if added to an acid base. The concentrations that I’m working with are miniscule, too. That said, micas containing it are marked clearly as not for use on the lips, & I wear a dust mask when using them. He can breathe easy 🙂

    And body butter is still in the shop! Just a few jars left…

  3. Anne says:

    Ha! I was just thinking about just this very thing! I had a few bars of Rosemary & Lavender turn pale pink on me because…guess!

    But hey, I actually kind of like how they turned out! You just never know what you’re gonna get, once you get to soaping sometimes!

  4. Hayley says:

    So, so true, Anne! I think as M&Pers we get used to a certain amount of what-you-see-is-what-you-get, compared to CP. Then we get all flappity when there’s a surprise 😉

  5. Loved reading this post, Hayley. It reminded me of my college days mixing glazes in the ceramics studio. I am so in love with materials and learning what they can and can’t do. Thanks for sharing your process!

  6. Kate says:

    I found this post really exciting, as I am deep into soaping (2 years and untold amounts of $) and one of my fairly new fascinations is cyanotype. I haven’t been able to justify the expense of the chemicals used in the art, of which the ferric ferrocyanide is one! You have no idea how excited I am that I now have an excuse to try this out! Thank you so much for posting, though I am a bit concerned about possible reaction. I’ll have to study up a bit more, I think.

  7. Jen says:

    Were you able to use the soap, even though the color was off?

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