Lye purity and lye aging

[Mobjack Bay]

I have been searching for a good discussion of lye stability, purity and the implications for superfat. I found what seems like very useful info embedded in a thread with an unlikely name:

https://www.soapmakingforum.com/threads/ash-or-mold-quick-responce-apprecated.46697/page-2

Here’s what I’ve taken away from what I read there and elsewhere:

• Lye degrades over time due to exposure to air and humidity. We can slow the degradation down by keeping the container closed tightly and not leaving the container open for longer than necessary.
• The lye should be discarded if it gets clumpy.
• For masterbatched lye, keeping the headspace to a minimum will reduce the rate at which the lye-water degrades.
• The lye we buy is probably not 100% NaOH, and the percentage of NaOH will go down over time due to exposure to/reaction with CO2 in air.
• Soap calculators don’t take the impurity of lye into account/assume the lye is 100% NaOH. This results in greater % superfat than calculated.

Am I on track?

Some of you are using lower SF in recipes. Is that to compensate for lye impurity or aging, because you like lower superfat, are trying to avoid DOS, or for some other reason? (I haven’t researched this topic very well, yet).

I’m using small containers of “Rooto” lye from Ace Hardware and emptying them pretty quickly (a few weeks at most and the container is stored in a sealed ziploc bag), don’t leave the container sitting open, and haven’t seen any clumping. I have seen the occasional dark specks. I’ve been leaving the SF at 5% when I use SoapCalc.

I looked for the chemical composition of Rooto lye and found this:
https://ace.infotrac.net/getmsds.aspx?sku=4239216 which possibly indicates 99% purity (on page 4). Am I reading that right?

Should I be correcting for lye impurity and lye “aging”? If so, is it reasonable to just drop down to 2-3 % SF?

I would be worrying about this less if I lived in Arizona. I live in coastal Virginia, and the hot humid months of summer will be here soon!

 

[Mobjack Bay]

Should I be correcting for lye impurity and lye “aging”? If so, is it reasonable to just drop down to 2-3 % SF?

I’m probably asking too many questions... This is the one that is most important. Thanks!

 

[DeeAnna]

Yes, you're on track.

Age has nothing to do with reduction in purity -- NaOH doesn't degrade purely due to time passing. Degradation is more about storage conditions -- how well you can control exposure to water vapor and carbon dioxide in the air. If you can store NaOH so it doesn't react with water and CO2, it will be fine for years, even decades, so there is no reason to reduce the superfat to compensate.

If you decide to reduce the superfat to compensate for reduced purity, it's important to have a protocol to make this adjustment, not just do this arbitrarily. @Susie talked about reducing the superfat some years ago, but IIRC she made this adjustment by tracking the weight gain of her NaOH. If the weight didn't change, no adjustment. I think she uses a dry bucket storage system nowadays, but I don't know if she still does any adjustment to superfat or not.

I don't adjust because I also use a "dry bucket" storage system. Since I've switched to that, I don't see clumping or weight gain. I also have tested the purity of the NaOH from time to time, and don't see evidence the purity is changing much, if at all. I'm using the last of a 3 year old purchase of NaOH that's been stored in a dry bucket since I received it.

As you can tell in this answer, I'm not overly worried about reduction in the purity of the NaOH I use. I use a low superfat (usually 2-3%) and also do an adjustment for NaOH purity, so my 2-3% superfat is closer to a true 2-3% than what you get from the online recipe calcs. My soap passes the zap test the day after making it, so that 2-3% is enough to ensure the soap is not lye heavy. For some recipes (laundry soap, for example), I've lowered the superfat to zero, and I can tell the soap is slightly more zappy (the zappy-ness disappears during cure). These results tells me my calculations are reasonably accurate.

I see no point to using a higher superfat except for soap that's high in coconut oil. For everything else, a low superfat works really well. The soap lathers better with lower superfat and the soap is plenty mild to the skin, so why would I want to increase the superfat? IMO, more fat make the soap more prone to rancidity. And more fat definitely reduces lather.

 

[Mobjack Bay]

@DeeAnna - this is what I was looking for! Thank you! I found one of your previous posts about “dry bucket” storage. That totally makes sense. In the lab, we keep chemicals like this in sealed cabinets with a desiccant.

 

[DeeAnna]

Yep, you're right -- the dry bucket method mimics a desiccator. It's not as good, but it's pretty decent especially if you use a bucket with a gasket in the lid so the closure is as air tight as possible. I use a "gamma lid" on a plastic bucket so I have a screw-on closure rather than the snap-on lids that are difficult to use.

(I have never missed the fun of dealing with those old-school glass desiccators with that sticky silicone grease!)

 

[LilianNoir]

Oh yay I'm glad this thread came up, it's quite timely.
Can we talk about degredation of lye solution purity?
I made my first batch of 1:1 solution a few weeks ago, and since the lye started reacting w/ the humidity in my air as I was pouring, I'm certain there was a bit of sodium carbonate in it but everything dissolved. I also weighed the solution after it cooled and added a bit of water to make up for the difference due to evaporation. (I lost about 5g)
I used that solution to make a batch with no issues.

Now, a few weeks later, the rest of the solution (which is stored in a tightly lidded #5 plastic Rubbermaid container, in an A/C climate controlled house) has crystallization coming up the sides of the container, and crystals on the bottom. I weighed it and it was slightly *heavier* than it should be. (.10 ounce)

This seems to point to sodium carbonate rather than lye precipitate.
If it is sodium carbonate, can I strain the solution and use a 0% superfat? Or is it best to dump it?

Further more, what can I do to prevent this?(Other than measuring lye inside because our humidity is so high)

The lye itself is stored in the double container method - lye in a tightly sealed container and that is inside of a tightly sealed bucket that also contains a dehumidifier.

 

[earlene]

LillianNoir, as my masterbatch lye gets low inside the bottle, it tends to have some precipitate also. I always shake the bottle well to re-dissolve any precipitate and that usually returns it all to solution. I have used a strainer a couple of times, but nothing that remained the strainer, so I don't usually do that anymore. I generally soap at 2-3% SF anyway, so I don't see a need to adjust my SF.

 

[Susie]

@DeeAnna I don't use the superfat adjustment now because I have no need. Even though I am using the "dry bucket" system, I still weigh and record the weight of the bottle before and after use. I was still having to adjust the superfat until we moved up to a dryer climate.

If someone suspects their NaOH is losing purity, it is important to weigh the NaOH after use (I write it down on a piece of paper that is wrapped around the bottle and held with a rubber band.) and again before use to know how much moisture it has absorbed. I then broke the weight gain down by % and adjusted the superfat accordingly.

 

[Mobjack Bay]

@Susie thanks for the tip on weighing the bottle of NaOH. I guess it gets heavier? Due to the lye taking up moisture from the air? Am I on the right track? Or totally off? So then if the lye gains X% of of original weight over time, you correct for the actual weight of the lye by subtracting the extra weight (percentage basis) due to the water?

Yesterday when I was mixing two batches of lye water for low and high water soap, I noticed that the low water solution developed a layer of something on the top, while the high water solution did not. Does anyone know why I would see a difference at the two different lye concentrations?

 

[DeeAnna]

Yes, it gets heavier due to moisture absorption. As to what Susie does to compensate, she'll have to answer that one.

The "stuff" on the lye solution is soda ash (sodium carbonate) due to reacting with CO2 in the air. I have no idea why there was a difference between the two lye solutions. Could be related to time exposed to open air, the solution temperature, or the lye concentration. Or the way you mixed the solution. Or ... who knows. I'd have to see what you did to maybe have some insight.

As far as what to do with soda ash -- I don't strain it out. I mix the solution well and use it as-is. The reason is that sodium carbonate was originally sodium hydroxide. Even though the carbonates don't care to react directly with fats without a lot of encouragement, they don't mind reacting with fatty acids. So, to put it informally, I put it all in the soap and let the different types of alkalis fight it out.

 

[earlene]

Yesterday when I was mixing two batches of lye water for low and high water soap, I noticed that the low water solution developed a layer of something on the top, while the high water solution did not. Does anyone know why I would see a difference at the two different lye concentrations?

The high water portion sinks because it loses water faster. I got that backwards - it rises while it gels, but if I recall correctly, it also got smaller or shrank faster during cure in my ghost swirl soaps. But I may be mis-remembering.

Here is a blog post by Auntie Clara where she talks about the high water portion getting puffy during CPOP. https://auntieclaras.com/2014/08/intentional-crop-circles-water-discount-as-a-design-tool/

 

[Mobjack Bay]

The "stuff" on the lye solution is soda ash (sodium carbonate) due to reacting with CO2 in the air. I have no idea why there was a difference between the two lye solutions. Could be related to time exposed to open air, the solution temperature, or the lye concentration. Or the way you mixed the solution. Or ... who knows. I'd have to see what you did to maybe have some insight.

I had two sets of everything side by side, measured out the water and then the lye for each portion and then mixed the lye into the water for each batch. It can’t have been more than 30 seconds between mixing one batch and then the next. I did not write down the order of weighing or mixing lye relative to the two different solutions. I will check to see if it happens again the next time I make the high water - low water soap.

 

[LilianNoir]

LillianNoir, as my masterbatch lye gets low inside the bottle, it tends to have some precipitate also. I always shake the bottle well to re-dissolve any precipitate and that usually returns it all to solution. I have used a strainer a couple of times, but nothing that remained the strainer, so I don't usually do that anymore. I generally soap at 2-3% SF anyway, so I don't see a need to adjust my SF.

Thanks @earlene! What're your thoughts on the weight increase for that solution? Do you think it's more likely to be sodium carbonate, precipitate or both? Should I try to redissolve and use it?

How does sodium carbonate affect soap/saponification?

 

[earlene]

I used to weigh my masterbatch lye bottles before & after pouring, but I don't anymore. So I am not really sure how much extra water weight there might be. But I also have not noticed any really noticeable difference in my soap made with the masterbatch lye that is at the end of the bottle versus the m.b. lye when it is brand new.

I just used up the last of my masterbatch lye this week and made more yesterday. Made soap with new m.b. lye today. So if I see any real difference, I'll come back and report. I am using some of the same recipes for both (older and newer) lye solution.

Regarding how sodium carbonate affects soap, I am not enough of a chemist to adequately address that question.

 

[DeeAnna]

...How does sodium carbonate affect soap/saponification?

Not sure what you are thinking when you ask this question, but I'll take a stab at answering. Sodium carbonate makes soap that's exactly the same as soap made with NaOH.

As I mentioned earlier, sodium carbonate (soda ash, washing soda) does not like to decompose fats into fatty acids + glycerin without a long period of gentle simmering.Once the fatty acids are created (or if you start with fatty acids to begin with), however, the sodium carbonate reacts easily with fatty acids to make soap.

The carbonate alkalis (potassium carbonate and sodium carbonate) have been used for centuries to make soap -- carbonate alkali is what you get when you make wood-ash lye -- so it's an established fact that they can do the job. You can also react them with slaked lime to convert them into the hydroxide alkalis (potassium hydroxide and sodium hydroxide) so they do a better and faster job of saponifying fats. The washing soda and lime method is sometimes called the method of "making soap without lye." That's a lie about lye if I ever heard one.

 

[LilianNoir]

Not sure what you are thinking when you ask this question, but I'll take a stab at answering. Sodium carbonate makes soap that's exactly the same as soap made with NaOH.

As I mentioned earlier, sodium carbonate (soda ash, washing soda) does not like to decompose fats into fatty acids + glycerin without a long period of gentle simmering.Once the fatty acids are created (or if you start with fatty acids to begin with), however, the sodium carbonate reacts easily with fatty acids to make soap.

The carbonate alkalis (potassium carbonate and sodium carbonate) have been used for centuries to make soap -- carbonate alkali is what you get when you make wood-ash lye -- so it's an established fact that they can do the job. You can also react them with slaked lime to convert them into the hydroxide alkalis (potassium hydroxide and sodium hydroxide) so they do a better and faster job of saponifying fats.

@DeeAnna that was exactly what I was looking for! Thank you! I'm a little embarrassed I didn't realize that myself.
Your answer was super thorough and really helpful because I like to know the how and why behind, well, everything.
For some reason I had it in my head that the sodium carbonate would be a "contaminate" in the soap.

Edit: I missed your earlier reply that addressed the interaction of sodium carbonate with the fatty acids. Sorry!!

The washing soda and lime method is sometimes called the method of "making soap without lye." That's a lie about lye if I ever heard one.

*GROANS* XD

Edit #2 because I have another question because OF COURSE I do.

I noticed @DeeAnna that you're calling sodium carbonate soda ash. Is that the same soda ash that can form on the top of soap? I'd always read that soda ash was harmless, but isn't washing soda still a bit too caustic to be touched with bare hands?

 

[DeeAnna]

Yes, the "ash" on the top of a bar of soap is often sodium carbonate (soda ash). Kevin Dunn suggests "ash" can be other chemicals besides sodium carbonate depending on what it is soluble in. Soda ash is soluble in water, for example.

 

[earlene]

I'd always read that soda ash was harmless, but isn't washing soda still a bit too caustic to be touched with bare hands?

In my experience washing soda is not too caustic to touch with bare hands. It is a bit drying to the skin, but your skin is not going to fall off or burn if you touch it and wash soon after. At least mine never did. I used to mix my home-made laundry detergent by hand without gloves and never any problems with doing it that way. I did usually wash my hands right away afterward and used hand lotion. Gloves would have been better, but I rarely wore gloves for household chores. I did that for over a decade, so not even any long-term effects were in evidence.

 

[DeeAnna]

I agree with Earlene. Brief exposure to washing soda will most likely be fine unless your skin is irritated or broken or if you have really sensitive skin. It will gradually dry the skin and eventually cause irritation, however, so it never hurts to err on the side of caution.

I don't usually wear gloves when working with dry washing soda, but if my hands are already dry and chapped, I do put gloves on to avoid any added dryness caused by the washing soda. I am also careful to avoid breathing the dust -- I work underneath my stove hood or work outdoors.

Here's a safety data sheet for Arm and Hammer washing soda -- https://www.menards.com/main/items/media/CHURC004/SDS/6471078_SDS.PDF