In natural soap making, coloring naturally your product is a big challenge. In this article I want to share with you the reasons why - after many trials and about two years of research, I decided to use methylene blue for... well,coloring soap blue :)
Blue is the most difficult to achieve in soap making when using natural ingredients. Actually, if you want a vegetal colorant, you have two options (that I know of):
- Alkanet (Alkanna Tinctoria) root infused oil - concentrate
- Indigo (Indigofera Tinctoria) root infusion
Alkanet is pretty unpredictable when it comes to the hues it can render. Most of the times, and especially if it's not concentrated enough, it comes out purple. Purple is good, of course, but sometimes I just want a plain blue :) Also, alkanet is at the current time not distributed in Romania. And the cost to order it from abroad is a bit prohibitive. Last year I received a small pack from dear Natalia, and for that I'm grateful, but I prefer to save it for lavender themed soaps ...
With indigo root I have the same problem. I can't find it in Romania, so I didn't have a chance to try its effectiveness.
Another solution would be to use mineral iron oxides. I tried that too. First of all, all mineral colors are pretty much reliable in soap, except this one. Sometimes, with blue oxide I obtained a pale green, other times a beautiful turquoise, other times blue. But it's pretty unpredictable. Also, mineral oxides tend to color the water too much.
I knew for a long time that other soap-makers were using methylene blue to color their soap. But they also said the color obtained is light sensitive. It fades in time, if exposed to light. Actually, this is the case with lots of natural colorants, too. Alkanet fades in time, carrot juice, spirulin, and the list could go on. I hesitated a lot before giving it a try.
But what is, actually, methylene blue? I didn't know much about it, except that it has some medicinal uses as antibacterial, disinfectant, etc. I also knew that mothers use it to treat throat inflamation, urinary tract infections and even dermatitis in their children, in order to avoid giving them antibiotics. So I went to Wikipedia for more details. It turns out that this is a pretty interesting chemical. It shows a "hormetic" dose-response, meaning that in small doses tends to have opposite effects than in large doses. If in large doses it is highly neurotoxic, in small doses it improves memory consolidation and has a neuroprotective effect. But this is just one example. Its uses in medicine are widely spread, and I leave it to you to discover them: http://en.wikipedia.org/wiki/Methylene_blue.
The fact that it's photo-sensitive doesn't bother me too much, because I now have these new fancy soap boxes that keep the soap colors light-safe until you decide to use it. And from the moment you expose the soap to light, you're granted at least another 4 weeks until the colors begin to fade substantially. I guess any soap can be consumed completely in four weeks.
Also, given its light antibacterial effect, in my opinion, it rather adds to the soap qualities. With all this info in mind, I finally decided to add it on my list of soap colorants.
There's just one thing I want to add: methylene blue should NOT be confused with methyl blue, another histology stain, new methylene blue, nor with methyl violets often used as pH indicators!