Dual lye in cp question

[Mobjack Bay]

I’m wondering how using dual lye (5% KOH, 95% NaOH) affects the longevity of a soap relative to using 100% NaOH for the same recipe. I’ve been able to find discussion threads on how using dual lye changes lathering qualities for a given recipe, but can’t seem to find any discussions on how it affects actual longevity in use under somewhat controlled conditions. I’m asking because I’m planning some trials. If experience has shown that the change in soap longevity is imperceptible in use, it would be good to know that before I decide on a calculated longevity (or range) for comparison.

 

[amd]

My somewhat controlled conditions:
3 people use my shower - myself, my daughter and the youngest son
Youngest son will only use unscented soap, so mostly he uses store bought body wash
Daughter will only use soap of particular "girly girl" fragrances
I am an equal opportunity soapist, so if it's in my shower I use it

Knowing this, last fall I compared a bar that I made with 95/5 with a 100 bar - same recipe, relatively same age (within 2 weeks of each other), chose fragrances that I knew my daughter wouldn't use (and being scented the son wouldn't touch at all), and put them in the shower at the same time. I alternated between the bars. The 95/5 used up faster - but one thing that contributed to this was that it also lathered quicker than the 100 bar, and being a creature of habit I lathered for the same amount of time, rather than stopping once I had a reasonable amount of lather to do the job. And yes, I cussed myself out every time.

That said, really the difference between the two bars life was that the 100 bar lasted approx 5-7 washings more than the 95/5 because of the way I used the 95/5. For me this was pretty negligible, so I do make some of my soaps with 95/5 (new fragrances, my old fragrances that I've been making for years stay 100) and customers have been happy with how quick they lather - to the point that they mention it. They do not mention that it doesn't seem to last as long, so either they do not have the issue that I had, or this isn't a concern for them.

As we all know in the soap world, these factors can (and do) vary greatly based on soap recipes, adjuncts, etc., so my experience with my recipe may not be repeatable for you in your recipe. I would definitely do a small batch test. I tested my 95/5 at about 5 weeks cure (the 100 bar was probably 7 weeks). I have not compared how they age - at 12 weeks, 6 months, etc. I'll have to check my records, I might have two batches that are close enough in age and well aged to do the comparison with, and I do have a couple bars in the shower that are almost gone... thanks for bringing up this topic, it's a comparison that would be good for me to revisit myself.

 

[AliOop]

I remember that @cmzaha used dual lye for many of her soaps that she sold. Carolyn, any wisdom to share here?

 

[Cat&Oak]

This is so interesting!

 

[Mobjack Bay]

Thanks @amd. This is helpful.

After a bit more reading tonight, I think I will set up two different comparisons using my current lard recipe as the “control.”

The first comparison with the control recipe will aim to find the point where a “modified“ recipe, using 5% KOH to balance an increase in palmitic + stearic, lathers like and lasts as long as the control recipe. I just modified the control recipe (longevity = 29) to longevity = 31 and longevity = 33 in an attempt to bracket the balance point. The range is just a guesstimate based on amd’s observations, new information (see below) and my experience making soaps in the 29 to 33 longevity range. The increase in palmitic and stearic is at the expense of a little oleic (from HO sunflower) in both of the adjusted recipes.

For the second comparison, I held the longevity at 29 in the recipe for the dual lye soap, but lowered the CO from 18% to 13% with increased oleic to compensate. I think that’s the only choice I have unless I lower the castor, but I need to look again when I‘m not tired, I may also try lowering the CO further, but not tonight!

If anyone is interested in trying dual lye, one of the threads I read on using dual lye is this one. The second post by @earlene links other threads on the dual lye topic and there are many more, such as this one. On a second reading of Earlene’s post, her comment about KOH not noticeably affecting the longevity of her soaps clicked. I also found this post and this one by @DeeAnna that address the soap life span issue. I must have missed them earlier because the posts are in threads on other topics. DeeAnna also posts about using dual lye to increase lather when CO is on the low side. Dual lye was a hot topic five or so years ago!

 

[Mobjack Bay]

I realized as I was trying to fall asleep last night that I should probably do a complementary comparison. For example, does my control recipe made with dual lye lather and last like a modified recipe with longevity = 27 or 25? I used dual lye with my lard recipe last week for a challenge soap. Based on early testing of an end cut, it seems to be making a more abundant lather relative to very early lathering of the same recipe made using only NaOH. Side-by-side comparisons of cured soap by people other than me will be the real test. I will need to be careful to make the dimensions and weights of test pieces as consistent as I can (note to self!).

 

[Susie]

I have found no difference in the longevity. I pretty much switch out between the 95/5% and the 100% depending on my availability of KOH. So, I have plenty of years to notice differences. And I have my testing of them somewhere around here somewhere to support those answers. Just have to find them. I was particularly looking for longevity comparisons because it is quite intuitive (to me) that the more lather would = a shorter longevity. That's not what I found. I was testing for selling, you see, and more lather + shorter longevity might = more sales.

 

[Mobjack Bay]

Thank you Susie! I know that I read a post of yours about dual lye soap going out to testers, but I couldn’t find any further info. I’m just terrible at judging soap longevity. With the many bars I have in testing rotation all of them seem to last forever. Whenever I test end cuts and small soaps, I think they lather a little differently compared with a full size bar.

 

[cmzaha]

I use dual in all my soaps and found no longevity difference or at least noticeable difference when I changed to using dual lye. In fact, it may have slightly helped longevity since it takes less time to kick up a lather so I need to use less water to lather up the bar. None of my long-time customers ever mentioned a difference either.

 

[Mobjack Bay]

Thanks @cmzaha! Maybe I can simplify this round of comparisons.

 

[DeeAnna]

Anecdotal experience here -- no double-blind trials or nuthin'.

I don't think using 5% KOH and 95% NaOH shortens the life of the soap I make by much. I agree with Susie that it seems likely the quicker, more abundant lather does shorten the life, but it's not obvious to the casual user. Most of my soap recipes contain a high % of lard, low coconut, and a moderate amount of oleic fats. I look at the dual lye option as an alternative to increasing the coconut oil and/or castor to get more abundant lather in a soap like this.

I think dual lye also improves the slimy, dense lather of a high oleic soap somewhat. This soap seems to lather quicker and the lather seems more airy and somewhat less gelatinous when I use dual lye. I strongly suspect dual lye definitely does shorten the life of this type of soap since it's already highly water soluble.

I wouldn't use dual lye with a soap that's also high in lauric and myristic acids. The soap is highly water soluble so it's already short lived, and it already lathers well. Dual lye won't do much good for this type of soap.

 

[cmzaha]

Here is the profile of one of my recipes:
Lauric 9 Myristic 4 Palmitic 23 Stearic 7 Ricinoleic 5 Oleic 40 Linoleic 10 Linolenic 0
Neither of my base recipes is high in Myristic or Lauric. My soaps lather well and are not slimey.

 

[AliOop]

Here is the profile of one of my recipes:
Lauric 9 Myristic 4 Palmitic 23 Stearic 7 Ricinoleic 5 Oleic 40 Linoleic 10 Linolenic 0
Neither of my base recipes is high in Myristic or Lauric. My soaps lather well and are not slimey.

You also use chelators, as well, yes? Does that help your lather, too?

 

[amd]

My recipe:
Lauric 9
Myristic 5
Palmitic 18
Stearic 15
Ricinoleic 5
Oleic 32
Linoleic 13
Linolenic 1

 

[DeeAnna]

Annnd here's mine --

Lauric 7
Myristic 4
Palmitic 20
Stearic 10
Oleic 47
Ricinoleic 0
Linoleic 5
Linolenic 0

The use of a chelator will increase the lather unless a person is bathing in super soft water, such as rainwater. A low (2-3%) superfat also increases lather.

For those who might be wondering, a chelator does not alter the solubility of soap. A chelator prevents lye-based soap from reacting with hard-water minerals to make soap scum. Soap doesn't lather well if it has to deal with hard water.

 

[Mobjack Bay]

Thanks everyone! I’m feeling good about being in this ballpark. The FA profile for my starting “control” recipe:

Lauric 9
Myristic 4
Palmitic 20
Stearic 9
Ricinoleic 5
Oleic 40
Linoleic 8
Linolenic 0

I use sodium citrate as my chelator.

I wasn’t using castor for a bit and then I had FOMO and added it back. I think another set of comparisons is in order with dual lye and no castor. I’m also in the midst of comparing the performance of this FA profile (or close on the p:s) in soaps made with five different hard fats or hard fat combinations (lard, tallow, palm, etc.).

 

[Tara_H]

Would this also help lather in a soap that was high on butters?

 

[Mobjack Bay]

Would this also help lather in a soap that was high on butters?

I think it would help in any soap with palmitic + stearic percentages in the 29, 30+ range as long as the recipe is not heavy in CO. Actually, DeeAnna mentioned that it will help high oleic soaps too, so it should help with lathering in any lower CO recipe. As I understand DeeAnna’s post above, it won’t help if the CO effect/lathering is high enough to overwhelm the increased lathering due to the dual lye.