On The Soap Making Forum, a reader asked about an apparent inconsistency with regards to the stearic acid. I made a point to say we want CAS 57-11-4 which is just stearic acid (within the limits of purity). He pointed out that while the CAS was right, the MSDS said it was a mixture of:
- Hexadecanoic Acid (CAS 57-10-3) 59.0%
- Octadecanoic Acid (CAS 57-11-4) 40.0%
- Tetradecanoic Acid (CAS 544-63-8) 1.0%
What is that alphabet soup you ask? Good question. Hexadecanoic Acid is Palmitic acid in International Union of Pure and Applied Chemistry (IUPAC) nomenclature. Octadecanoic Acid with its CAS of 57-11-4 should look familiar; that’s Stearic acid. Tetradecanoic Acid is Myristic acid. So it turns out this is exactly the thing I told you we don’t want.
I emailed the customer service address for Lotioncrafter and the owner, Jenny Welch and I exchanged a few emails. She shared with me, well, let me share exactly what she said:
“I consulted two cosmetic chemists that were well known and trusted in our industry and both recommended that I bring in Emersol 7036 Stearic Acid NF which was, and still is, the one most often used by cosmetic formulators in formulations calling for vegetable based stearic acid.”
She was very up front about everything, and I want to be clear the error is MINE because I did not read their MSDS; I stopped reading after seeing the CAS number I wanted. She is coming at this from the point of view of someone making cosmetics and I have no doubt what she says is true. To a person not saponifying the fatty acids this is just a matter of semantics and it makes no difference since to them this is stearic acid. And, to be fair the manufacturer also lists the product as having CAS 57-11-4, but then follow up with the same ingredient list if you read into it more. It’s confusing to me, maybe there’s a reason. Either way Jenny updated her website to reflect the three CAS numbers just because she thought it was the right thing to do.
Lotioncrafter came highly recommended to me and I can see why. It is tough these days to do business online and still be responsive to people. Just because you can order things now doesn’t mean people are waiting now to answer your questions. Jenny was very prompt with her initial and follow-up emails though, surprisingly so. In my book this simply solidifies the high praise with which she was recommended to me.
Incidentally, Emersol makes EMERSOL® 153 NF which is ~95% stearic acid (plus some impurities). I asked Jenny if I purchased a whole bag if she could drop ship it. As I feared, she buys only by the pallet and I don’t need a pallet of the stuff. Buying in large quantities is how she keeps the cost down for what would likely be very expensive to us otherwise. It looks like I will have to live with a different product from now on. Shame on me for not being more thorough!
Now I have more questions. You see, Palmitic acid has a lower molar mass than Stearic. This means that there are more molecules of Palmitic acid per a given weight than Stearic. For the really geeky folks: The molar mass of Palmitic acid is 256.4241 g/mol where Stearic acid is 284.4772 g/mo. For every molecule of a fatty acid we need one molecule of lye. In our case that lye is KOH or Potassium Hydroxide. The ratio of the two is the SAP value. We can figure the SAP value of this new product if we know what the molar mass of the components are because it is the ratio of the weight of the lye molecules to the weight of the fatty acid molecules. So, for each:
- Lye (56.1056) / Palmitic Acid (256.4241) = 0.219
- Lye (56.1056) / Stearic Acid (284.4772) = 0.197
- Lye (56.1056) / Myristic Acid (228.3709) = 0.246
“Great” I hear you saying; “now what?” We multiply those by the percentage of each in the product, and add them together to get our new SAP value. Our values look like this:
- 59% Palmitic @ 0.219 = 0.129
- 40% Stearic @ 0.197 = 0.079
- 1% Tetradecanoic @ 0.246 = 0.002
Add those and we get a new SAP value of 0.210 for our work. See how relatively simple that is? What does this mean for our soap?
Soapcalc has Stearic acid at a SAP of 0.198. The new product I have has a SAP that’s ~6% higher. The original recipe used Stearic acid at 45% so that’s an effective difference of ~2.7%. Our superfat was calculated at 5% so it does raise the superfat from 5% to ~7.7%. The difference is small. We’ve also got a different fat makeup now; the difference in the fat profile is pretty simple. The new formulation is +18% Palmitic and -18% Stearic compared to the original.
Both Palmitic and Stearic acid contribute dense stable lather and a harder soap to the mix. To most soapers the two are interchangeable. To settle it, I did what I said I was not going to do in the other article: I re-formulated. I made three small test batches:
- A test batch with my original (now dwindling) supply of straight Stearic Acid
- A test batch switched 1:1 with the Lotioncrafter product
- A test batch with lye adjustments made to take the different fats into account
The testing was randomized and I shaved three times with each one and recorded the results. This was done to help even out the effect of the soap as it ages since it was used relatively soon after the cooking.
- The first shave cycle had one sample just maybe being a tiny bit drying. It was still a good shave and all had very similar lather otherwise.
- The second shave cycle I thought maybe there was a difference but as I looked back at my notes I realize I was just kidding myself.
- The third shave cycle was much like the second. Maybe, just maybe, one was a tiny bit drying. All were good enough to put my name on them though.
When I peeled the tape off the labels, I discovered that in round one I did score batch #2 down just a tiny bit. In round 2 the one I thought maybe was a tiny bit drying was the original (#1). The difference was so slight that it could simply have been a difference in the humidity. By cycle three the one I thought might be drying was again sample #2, the straight swap.
The winner was basically a tie, there was not enough difference to say one way or the other. A better test would include more shaves, different people, all that mess. Since I make this for me I see no reason not to use the Lotioncrafter product going forward. If you do a test, do let me know what you think.
The old recipe was:
- 45% Stearic Acid
- 25% Coconut Oil
- 20% Tallow
- 5% Shea Butter
- 5% Lanolin
The new one, adjusted for the Stearic Acid available to us, is below. If you use SoapCalc you will notice that there is only “Styearic Acid” which aligns with the values for straight Stearic. I did forward them a request to list the Stearic Acid NF, and they will whenever they do an update. In the meantime you need to put in the three component fatty acids so the recipe is:
- Stearic Acid NF; which would be represented like this in SoapCalc:
- 26.55% Palmitic Acid
- 18% Stearic Acid
- 0.45% Myristic Acid
- 25% Coconut Oil
- 20% Tallow Beef
- 5% Shea Butter
- 5% Lanolin
Then, you will add together the weights for Stearic Acid, Palmitic Acid, and Myristic Acid and that total weight is what you will use for your Stearic Acid NF addition. We go into this with the assumption that properly balanced; the Palmitic/Stearic/Myristic mixture will perform the same as the Stearic formula of the original recipe. We therefore use the same percentage (45%) but now we split it up between the three components in Stearic Acid NF so that SoapCalc will figure the lye correctly. If you compare the two recipes through SoapCalc the oil weights will be the same, but the lye is slightly different. We had to balance for the different SAP value of the new product.