Clay, Essential Oils, and Soap – An Experiment

Some people exclusively use essential oils to scent their soaps. I don’t, for a couple of reasons. 1) They are medicinally active and you really need to know what you are doing to use them safely (see this post for more on essential oil safety). 2) They tend to be quite a bit more expensive than fragrance oils and your options are limited by price and availability (there just isn’t an essential oil that smells like coconut or pears, for instance). 3) Often times, the scent tends to fade rather quickly in your bar. That grapefruit essential oil soap that smelled amazing when you cut it six weeks ago? Three months in it now smells like, well, soap. I DO have several all essential oil soap offerings though (Lavender-Lemon, Fresh Lemon, Rosemary Mint and Peppermint, and occasional seasonal mixes like Orange-Patchouli), and am always looking for new combinations to try that won’t break the bank and will hold up over time.

When the “how do I get essential oils to stick in my soap” question comes up in soap making groups, the answer from the soaping brain trust is almost always “use clay to anchor the scent”. I’ve seen it repeated over and over and over in the last 8 years. And so I started asking, has anyone ever done a side by side comparison with and without clay? And the answer was almost always no, or an anecdotal “I can tell the difference”.

New Directions Aromatics 5x Lemon

I don’t discount that clay could have an effect. It’s incredibly small, easily hangs onto liquid and then only grudgingly releases it, and the surface tends to be negatively charged – which is why it can be important in your soil composition when it comes to minerals in the soil and their availability. Clay particles tend to hang on to positively charged minerals like calcium and potassium. But this would mean that at least some of the chemical components of the essential oil would need to be positively charged in order for the clay to chemically bond with them. Given that one essential oil can have many many different chemical components, that becomes a bit of a roll of the dice (or at least a lot of research and a basic knowledge of organic chemistry). For instance, here’s a list of the major chemical components of lime essential oil:

• A- Pinene
• B-Pinene
• Sabinen
• Myrcene
• Limonene
• y-Terpinene
• Terpinolene
• Octanal
• Nonanal
• Tetradecanal
• Pentadecanal
• Trans-a-bergaptene
• Caryophyllene
• B-bisabolene
• Geranial
• Neryl acetate
• Geranyl acetate
• a-Terpineo
• Linaloo

Yeah. That’s a lot of research.

So, being the scientific minded individual that I am, but not wanting to dive back into organic chemistry after a 20+ year hiatus, I decided to do an actual side by side test using an essential oil that is known to fade; lemon. And recognizing that my nose isn’t really all that great, I decided to recruit 11 volunteers from my soapmaking groups to help me with the smell test.

Testers were pretty spread out across the country, and were asked to record temperature and humidity, in case that factored in.

I made a batch of soap on March 9th using some old shea butter that was likely about to expire, just to use it up. All bars were scented with 5 fold lemon essential oil (a lemon that has been concentrated, ie folded, for better longevity in soap) at a radio of 1 oz per pound of oils in the recipe, made with a 35% lye concentration. One soap contained no clay. One contained kaolin clay (chemically, kaolinite, Al2Si2O5(OH)4). One contained bentonite clay (also called montmorillonite or sodium bentonite, Al2H2Na2O13Si4). And one contained kaolin clay, where the essential oil was combined with the clay and allowed to soak for about 30 minutes before it was added to the soap batter. Clays were used at a 1 tsp per pound of oils ratio. Each soap bar (three bars of each example) was cut into quarters and numbered, for a total of 12 of each sample. Samples were numbered 1 to 4. Then a set of each was mailed to my testers about 4 weeks later, once the soap had cured. Soaps were shipped in bubble wrap envelopes, wrapped together in a cloth bag. Likely they were all stored together in the cloth bag between sniff tests.

Testers were:

• Lisa BB
• Laura F
• Tonya LH
• Carolyn M
• Marie N
• Marilyn FP
• Rosemary R
• Michelle OS
• Shirin S
• Kim S-N
• Lisa W
• and Me

Unfortunately, it became clear shortly after the shea soap was mailed that the shea was going rancid. You could smell it had gone off. Nasty, and masking the lemon scent significantly. Darn it. Back to the drawing board.

More soap was made on April 18th, using my standard olive/coconut/palm/rice bran/castor recipe, and mailed out again about 4 weeks later. I asked my testers to continue testing the original shea batch once a month, and to do the same tests with the second batch, ranking them from strongest to weakest on a monthly basis for six months. No one knew which soap contained what ingredients. They were asked to report to me individually, so that no trend from other sniffers biased the reports.

And then real life happened. My testers, with the exception of two, flaked out on their reporting. Yeah, that’s right. Ten people who were super excited about this experiment (OK, two of them were personal soaping friends who I roped into it), and promised to regularly report, in the end, didn’t send me their data. When I made a final appeal, on February 15th of this year, to please report if they could tell any difference between the bars at this final point in time, and gently forgave them if they had not kept up with regular recording up until that point, three responded that they couldn’t tell the difference between the bars, but that it must have been that they just “didn’t have the nose for it”. One threw the rancid samples away shortly after they started to turn.  So materials, time and about $60 in postage later, I’ve got very little in the way of results. I’m sure they had good intentions. But I recruited based on people who claimed they had a good nose (mine isn’t all that great). I think that when in the end, when they couldn’t tell them apart, they thought it was a personal failing on their part and so stopped reporting. Which makes me sad.

THANK YOU Marie N and Lisa BB for your follow through, and Lisa BB for reporting your really interesting observations on the rancid samples!

Speaking of which, Lisa BB noticed that with the rancid samples, not all of them were turning orange (a sign of rancidity) at the same time. Number 4, the one with bentonite clay, was turning less quickly. When I looked at my own samples, I saw the same thing. I asked the other testers to check their samples to see if they had similar results. Crickets…

Photo compliments of Lisa BB.

So, its possible that bentonite clay has some rancidity retarding properties. Wouldn’t that have been interesting to confirm with the other 10 testers? Science doesn’t mean getting the results you expect, it means observing and trying to make sense out of the results you see.

For those who did report in the end (a total of 5 of us, including me), they could not tell the difference between the bars with or without clay, or the difference was incredibly subtle. Mine DO still all have a faint lemon scent, but they all smell the same to me as well. In other words, nothing dramatic between those with and without clay.

So, my unfortunately not very scientific results? The advice of adding clay to “anchor” your fading essential oils scent in soap does not work. Clay doesn’t make a bit of difference for scent retention, at least when using 5x Lemon essential oil.

Miles Away Farm Blog © 2018, where we’re miles away from exploring all of the possible essential oil combinations in soap, but are happy that fragrance oils also exist. And I promise, the next post will be about lamb babies. We have one set of twins, and expect the rest to be born in the next few weeks!