Soda Ash, Mould, or not? A discovery onto aged leather-bound books

I made facial hot process bars in March using colloidal silver as full fluid and have kept them in storage to cure. I usually only do cold process soap bars, however I needed to hot process this batch to test a granite or marbled effect using activated charcoal, which turned out beautifully.

Waiting for a lovely sunny day (and getting side-tracked for a while) have delayed me taking them out to take photographs. Much to my dismay this afternoon when I saw the opportunity to take some nice stock photos outside in the sun, I took them out of their cardboard boxes and found every single bar covered in what seemed to be a powdery efflorescence.

The pH of soap bars should discourage the formation of mildew, fungus or mould and since I added colloidal silver which is supposed to aid in the prevention or the treatment of fungi, I was floundering for answers.

Quite bemused with myself, and frustrated since I couldn’t verify my recipe due to contractors working on our electricity and thus my recipe being unavailable on my computer, I spent the rest of the afternoon trawling through Google trying to find information. For obvious reasons, searching mould or mold and soap returns results about moulds – the type that you pour your soap batter in 😉

It clearly didn’t look like soda ash, having tiny little white flecks which when you zoom in with your camera, looked almost feathery, however I have seen people advising members on soap forums that it perhaps may be. And the soaping theory is as well that hot process bars *shouldn’t* produce soda ash since the saponification is completed during the cooking process. Soda ash is the formation of a thin white film over soap, which happens when you soap with too much water, and when the surface of the batter is exposed to colder air which forms sodium carbonate.

So, I did a few “sciencey” experiments…
Experiment #1:
This was just a simple wash test to see if the efflorescence would wash off, which it did somewhat. This could mean that it’s soda ash, or mould either way, so I wasn’t anywhere nearer to an answer.

Experiment #2:

This again was just a simple dissection to see if the white particles were found inside the bar, which they weren’t. I was mildly relieved, as I somehow thought this proved it wasn’t mould for some reason.

Experiment #3:

Soda ash is washing soda or sodium carbonate, it should fizz in the presence of vinegar. I tested this theory with a few granules of washing soda, and yeap, it fizzed.
Watch a video of the experiment here.

I found an old bar that had soda ash on, so I cut the top piece off and dropped it in a fresh cup with apple cider vinegar, and after a short while, a few errant bubbles started to appear. Definitely not as fervent as pure washing soda, but still a bit of a fizz.
Watch the experiment here.

Next step was to test the new bars, so I repeated the same process, and nothing. Not even a single bubble emerged, which proved that it’s not soda ash. Watch the experiment here.

At this point I was starting to worry that is indeed mould, so I grabbed my phone and carry on with my research while anxiously waiting on electricity to be restored. I searched for microscopes at one point (LOL), and then DIY tests to test for mould, which didn’t provide much information other than home tests you have to buy.
Thinking that perhaps the silver ionic particles from the colloidal silver might be reacting with the sodium hydroxide somehow, I changed my search criteria, and somewhere along my dozens of search criteria including metal deposits, I stumbled across a photo of an old leather-bound book, with exactly the same efflorescence.
I had bit of a “yay” moment I must admit 🙂
The article was about a special selection of books at Miami University which were found to be covered in white leather bloom, otherwise known as spue:

‘According to the Alaska State Museum’s blog, “What’s That White Stuff?” spue is a “white bloom resulting from fats, oils and waxes and may be referred to in the literature as fatty bloom, or fatty spue (spew). These terms all refer to the migration of fats/oils through the leather material that crystallize on the surface in the presence of air.” ‘
Link for Miami University’s article over here:

Experiment #4:

In essence, there are two types of bloom/spue, fatty or waxy spue, or salt spues. Since the former is easy to verify, I set about my next experiment, which involved holding a heat source to the spue. If it melted, then it’s a waxy spue. So, I hunted for a lighter and et voilà! It melted and left an oily residue on the bar.
Watch the final experiment.

Admittedly I was quite relieved at this point that I didn’t have mould all over my bars, and quite chuffed that I had found the source of my distress for the day.

The article furthermore states:
“There are different opinions about the formation mechanism of the spues, although everybody agrees on the differences in the displacement of different fat components into the leather. Papers on the subject agree that the fatty acids and their esters initially form as a dissolved material in the liquid phase, with the liquidic oil acting as a solvent at room temperature. They come from natural fats and from fat liquors added in the process. This solution becomes oversaturated due to a high concentration of fatty acids and esters and/or to a fall in the room temperature. As a consequence the fats migrate to the outer surfaces of the leather and crystallisation of the fatty acids and/or glycerides occurs. The concentration of the acids and esters is due to a differential solubility of the components in the leather. The liquid oils are either partially or totally reabsorbed in the fibre network while the crystallised fatty acids and glycerides remain on the surface.”

For all those soapmakers out there, this sounds like soapmaking, right? Since the article further describes the theory behind the formation of the spues on leather being the application of oil to treat and preserve leather, I would assume that there is possibly an excess of oil in my recipe in the form of superfat* which migrated outwards.


At this point, I was able to pull up my recipe (electricity restored, happy dance!) and I see a superfat* of 7.5% which isn’t too high, however, this hasn’t presented an issue doing them as cold process bars before. (*Superfat is what we “soapers” refer to as “excess” oil in soap, and is what gives soap it’s gorgeous conditioning properties).

Perhaps I had an elbow-jerk moment when I added my oils which could have resulted in too high an excess oil over all and I didn’t make a note of it?

Perhaps storing them in a cardboard box, with our drastic humidity or cold weather changes in our Capetonian winter period currently added to the migration of unsaponified oil outwards, and next time I should rather keep them in an open area? (Unsaponified oil is essentially oil which isn’t turned to soap during the soapmaking process “saponification”).

Perhaps it was just luck of the draw, who knows? Sadly, I’m no scientist, and I’m sure someone with more experience can offer some insight.

For now, I am just happy that I don’t have to discard the bars as I despise waste, although I would probably observe them carefully in case spoilage sets in at a later stage due to the possibility of unsaponified oil. Only time will tell.

Edit: The bars were fine 6 months after this article was written, and interestingly enough, 2 more bars produced more fatty bloom/spue. I’ve subsequently found it to be more common in soap bars container higher amounts of butters like cocoa butter (chocolate bars can get fatty bloom too!) and shea butter, which these bars had a hefty portion of.

Soapmaking is fun and interesting, isn’t it!

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