It’s unbelievably frustrating to create a brightly colored handmade soap only to see the color morphing over time into something completely different, something dull or muted and boring. What causes these changes?
It’s all about the pH! Handmade soaps are alkaline with a pH of 8 or higher, while most of the other bath and bath and body products we make, like facial products, lotions and hair care products, have an acidic pH of 3.5 to 6. Choosing the right colorant for the pH range of our products – micas, water soluble dyes, oil soluble dyes, powdered pigments, micas, iron oxides, ultramarines, lakes and so on – can mean the difference between a brightly colored soap or bubble bath and one that’s muddy brown or grey, so it’s worth the time to learn a bit about your pigments before you use them.
The product in which we see the most color morphing is handmade soap, an alkaline product created through the process of saponification. Over eight to ten weeks – sometimes longer – the strongly alkaline lye reacts with fatty acids in the oils to create soap, and the pH decreases. Any colors you’ve used that like a more alkaline environment or those that prefer a more acidic environment can change very easily from bright to dull, vibrant to brown or grey. To avoid this heartache, choose dyes, pigments and botanical ingredients that work well in an alkaline environment.
For all manner of handmade soaps, the most stable choice for colorants are pigments, like iron oxides. They produce natural earth tones like brown, yellow, brick red or black, and don’t tend to migrate from one layer to another. Ultramarines like pink, blue and purple; chromium oxide (green); and chromium hydroxide (teal green) are also good choices, and they offer slightly brighter colors without migration or morphing.
Natural colorants, like charcoal or clays, and powdered botanicals like roots, flowers and plants are a great addition to alkaline soaps, but the latter can morph over time if they contain certain polyphenols, called anthocyanins and anthocyanidins, found in red, blue or purple pigments of fruits, flowers and vegetables, like grapeseed, strawberry or acai extracts.
If you’d like to see the color changes of these polyphenols, try this experiment with red cabbage as a pH indicator. Add 2 to 3 cups of chopped red cabbage to water, bring to the boil, then let it sit for up to 30 minutes. Strain off the bright red liquid. Pour out three glasses of water, and add baking soda (alkaline) to one and citric acid or vinegar to another. Add the cabbage juice to each glass and observe what happens! At below pH 3 or very acidic, the liquid is red, and shifts to pink as the pH increases. At neutral pH (7), it appears violet or purple, then shifts to blue as the pH increases to the alkaline range. (This is why a very red-brown grapeseed extract soap morphs into a blue bar after saponification!) These polyphenols are stable in acidic products.
If you prefer more vibrant colors, it’s tempting to buy FD&C dyes that can be found as liquids or powders, but resist the urge! They’re fantastic in acidic or neutral products, but in alkaline environments they aren’t very stable and can morph to produce a boring brown quite easily. Instead, look for liquid or powdered ingredients suitable for alkaline products, like high pH LabColor dyes.
If you’re into bright, shiny colors, consider using micas, which produce brilliantly hued soaps all the colors of the rainbow, as well as metallics and pearls. These mineral based powders will make your soap pop and shine, but there’s still the potential for morphing if they derive their color from FD&C dyes. Before using micas on large batches of soap, do a small test or consult your supplier or supplier’s site for more information on color shifts.
Morphing can happen in acidic products, although it’s much less common. Body washes, bubble baths, shampoos, some melt & pour soap and any other products made with foamy, bubbly, liquid surfactants should have a final pH of 6.0 or lower to match the pH of our skin and hair. Bath bombs can have a slightly acidic to neutral pH depending on composition – my bath bombs with a 2:1 ratio of sodium bicarbonate (base) and citric acid have a pH around 6.6.
In these products, you can use all manner of colorants that stay stable over time. Micas are all about the shimmer or shine, creating slightly opaque products. FD&C dyes create “gummy bear” or “stained glass” looks in clear products and pastels in white. As they’re water soluble, they can migrate through layers in soap. Lakes, which can be found as powders or dispersed in water or oil soluble liquids, can produce incredibly vibrant colors with less bleeding in all kinds of products, especially in bath bombs and bubble bars, but they’re unstable in light.
There are a few things that could interfere with the color or brightness in acidic products, like choice of citrus fragrance or essential oils, use of vanilla or exposure to light. For the latter issue, keep products in a bag or cupboard until you’re ready to use them.
Choose your colorant based on the pH of your product or choose your product based on your preferred colorant: Either way, you’re ensuring the color you’ve chosen stays true to your vision.