Making Hard Soap with Potassium Hydroxide (KOH)

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Richard Perrine

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Not certain if anyone is interested, but I have been on a mission to explore lately and just discovered an interest in making soap with KOH instead of NaOH. Trying to determine the differences and pros/cons. I also had a container of KOH that i needed to use as I decided not to get into liquid soap making. :) Here are my first tests:


The first image is my citrus blend CP soap a couple of minutes after pouring. It was pretty stiff. After a few minutes, it softened greatly and heated up. It was gelling! I added glycerin, so the sugars undoubtedly contributed to the heat. I poured another KOH soap w/o the glycerine and it solidified quickly and w/o softening (soap on right). I refrigerated the bars for about an hour and pulled them out of the mold. A little sticky, but not bad.
 
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Are you only using KOH? There are some members here who use KOH at 5% (+ 95% NaOH) to make bar soaps with a lot of success. If you are using only KOH, I doubt it will hold as a bar.
 

Richard Perrine

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Are you only using KOH? There are some members here who use KOH at 5% (+ 95% NaOH) to make bar soaps with a lot of success. If you are using only KOH, I doubt it will hold as a bar.

Hi. Yes. 100% KOH. I also thought about various ratios with NaOH. Do you know why some use 5% KOH? How would that little amount benefit?

The bars were pretty stiff this morning. I will let them sit for a few days to cure and see what happens.
 

DeeAnna

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You've basically made KOH soap paste. If you want to use it straight, it can work fine for bathing and household cleaning. Search for Susie and her "Soap 2 Go" suggestion. Also see discussions here about "beldi" soap.

Undiluted paste can be a firm gel (like Jello made with less water than usual) or it can be a sticky and slightly softer (but not pourable) paste. It's never going to be hard like NaOH soap.

Regarding the use of 5% KOH in bar soap -- Here's a thread I started: https://www.soapmakingforum.com/threads/dual-lye-castile.59747/ There are other reasonably recent threads that will pop up on a search. Also see https://classicbells.com/soap/dualLye.html
 

Richard Perrine

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You've basically made KOH soap paste. If you want to use it straight, it can work fine for bathing and household cleaning. Search for Susie and her "Soap 2 Go" suggestion. Also see discussions here about "beldi" soap.

Undiluted paste can be a firm gel (like Jello made with less water than usual) or it can be a sticky and slightly softer (but not pourable) paste. It's never going to be hard like NaOH soap.

Regarding the use of 5% KOH in bar soap -- Here's a thread I started: https://www.soapmakingforum.com/threads/dual-lye-castile.59747/ There are other reasonably recent threads that will pop up on a search. Also see https://classicbells.com/soap/dualLye.html
Yikes! Thank you DeeAnna! I will certainly read-up on this!
 
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Just a side-note Richard ... the plastic coated wire racks are great, but if there's even the slightest nick in the coating, the soap can react with the metal underneath and that will almost always lead to DOS.

A simple cotton teatowel (or similar thick cotton material) can be enough to lift the soap away from danger :)
(unless the soap weeps, then a moisture barrier becomes necessary).
 

Richard Perrine

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Just a side-note Richard ... the plastic coated wire racks are great, but if there's even the slightest nick in the coating, the soap can react with the metal underneath and that will almost always lead to DOS.

A simple cotton teatowel (or similar thick cotton material) can be enough to lift the soap away from danger :)
(unless the soap weeps, then a moisture barrier becomes necessary).

Thank you. I will make adjustments.
 

Richard Perrine

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Just a follow-up. The bar that included the glycerine continues to be a little soft, but is hardening. The bar on the right, w/o glycerine, appears pretty firm. I will wait a couple of days to see if the bar with the glycerine becomes harder and then test soaps later in the shower.
 

Richard Perrine

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Update.
koh-soap-test.png
My latest KOH soap test recipe set much quicker than I anticipated. After adding the mica coloring and fragrance oil, I really had to work fast. As you can see, I didn't work fast enough. I plopped and tried to settle the soap into the mold, but after about 10 minutes in the freezer and unmolding, the soap set too quickly to properly fill the form. I will work quicker.

The previous soap with glycerine is still soft and doesn't look like will harden much more. It remains a stiff paste-like bar. But, my bar w/o glycerine is as or close to as hard as my NaOH soaps. I also took the pH of both earlier soaps and they are closer to a pH of 8 (possibly closer to 7 after a few more days of curing???)! None of my NaOH bars are that low even after many weeks curing. The initial pH of the KOH soaps were as high as the NaOH, but after 3 days, they have dropped greatly! Significant, no? What kind of affect would that have on your skin, I wonder? Any significant difference? Can't wait to try.
 
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It's interesting reading your observations ... I'm enjoying your experiments :thumbs:

Just a little side note: Lye and soap batter dissolve glass (and silicone too) very slowly. Silicone just breaks down (deteriorates), but glass can shatter eventually (especially the newer glass - the old borosilicate glass was more resistant, but the newer glass isn't nearly as resistant to the chemicals).

It is better to use either good quality stainless steel or #5 plastic (polypropelene) to mix your soap, as they are both heat and chemical resistant (to lye).
I personally use stainless (it's virtually indestructible in the soaping context), but most people like PP.
#2 plastic can be used in a pinch (HDPE), but it doesn't have nearly the same heat resistance (don't let it get hot or it will melt).
 

Richard Perrine

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It's interesting reading your observations ... I'm enjoying your experiments :thumbs:

Just a little side note: Lye and soap batter dissolve glass (and silicone too) very slowly. Silicone just breaks down (deteriorates), but glass can shatter eventually (especially the newer glass - the old borosilicate glass was more resistant, but the newer glass isn't nearly as resistant to the chemicals).

It is better to use either good quality stainless steel or #5 plastic (polypropelene) to mix your soap, as they are both heat and chemical resistant (to lye).
I personally use stainless (it's virtually indestructible in the soaping context), but most people like PP.
#2 plastic can be used in a pinch (HDPE), but it doesn't have nearly the same heat resistance (don't let it get hot or it will melt).
Thank you for that information! I will make the transition.
 

KimT2au

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glass can shatter eventually (especially the newer glass - the old borosilicate glass was more resistant, but the newer glass isn't nearly as resistant to the chemicals).


Ahhh, when I was looking at some shopping specials some glass bowls were listed as borosilicate glass and I did wonder what that meant. I was not curious enough to go check though. Now I know.
 

plhamp

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Richard thanks for the experimenting and feed back. It reminded me of Grandma's explanation to me of how they made their own soap when she was little. They used lye made from wood ashes which is potash or potassium hydroxide. To harden it into bars she said they added table salt after it all came together. I did find a page about making soap from lye made with wood ashes and it says to add 1/2 tsp. of salt per pound of oils in your lye mixture to make you soap bars harder. http://www.countryfarm-lifestyles.com/make-lye.html#.W7o9yXtKiHs
 

Richard Perrine

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Richard thanks for the experimenting and feed back. It reminded me of Grandma's explanation to me of how they made their own soap when she was little. They used lye made from wood ashes which is potash or potassium hydroxide. To harden it into bars she said they added table salt after it all came together. I did find a page about making soap from lye made with wood ashes and it says to add 1/2 tsp. of salt per pound of oils in your lye mixture to make you soap bars harder. http://www.countryfarm-lifestyles.com/make-lye.html#.W7o9yXtKiHs
Hi. Yes! Salt is the 'secret' ingredient! I have found that 1/2-tsp per pound is way too little to create stiff bars. It could also be that my concentration of potash or KOH is lower so that would explain the larger amounts I use to create the hard bars I make. I'm not re-inventing the wheel here, so my reference point was from here:

http://naturalsoapandhomemadeproducts.blogspot.com/2016/02/potassium-hydroxide-salt-bar-soap.html

GREAT information. I have modified the recipe he gives somewhat. Curious enough, I decided to investigate KOH soap b/c of my wine soap tests. I thought using some other soap making process would help me, so I looked this up. I remember DeeAnna answering a question another poster put up about KOH soap and how much was required to make solid soap from it and that also triggered my interest. What I like about this method is that it's helping me find another use for my KOH flakes as I've decided not to embark in liquid soap-making and its pH drop only after a couple of days. I haven't started, but I wonder how KOH soap compares in terms of retaining fragrances, etc.

Thank you! If this soap proves to be more gentle to the skin and perhaps the ingredients used, I may make a transition to KOH soap or make it a part of my amateur soap-making arsenal. Is it possible that KOH is less harsh all around, so allowing essential oils and fragrances to last longer?

I am also aware that it may not be cost-effective to use KOH for hard soaps. It requires much more and the price seems to be about what you'd pay for NaOH, maybe more? As I am not selling my soaps, I have the luxury of experimenting for fun. :)
 

Richard Perrine

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I decided to do something with the soap that isn't going to harden. Cut into small cubes and placed in a dispenser, warm water and voila! Liquid soap. :) I believe that is the point of soap paste???
soap.paste.dispenser.jpg
 

plhamp

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You can also look up how to make glycerin, which is basically the same ingredients - water, lye, oil and salt. After the soap comes to trace stir in salt while still hot and then let the mixture set off heat. The soap rises to the top and the glycerin settles to the bottom. Scoop off the soap from the top of the bottom syrup like liquid which is glycerin. Might make your potassium bar soap harden up quicker. My skin appreciates the glycerin left in my soaps though.
 

DeeAnna

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At trace, the saponification reaction is only partly done -- maybe 10% to 20% finished -- so why would you want to salt-out the soap at that point? It's mostly fat and lye solution, not soap. Much better to wait until the saponification is fully finished. Also the "glycerin" you get from salting out soap is a brown liquid contaminated with salt, a fair bit of water, and water-soluble impurities. I've seen modern tutorials that imply this stuff is the same as the clear syrupy drug-store glycerin ... but it's really not even close.
 

plhamp

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Might make your potassium bar soap harden up quicker. My skin appreciates the glycerin left in my soaps though.
Just a suggestion that might help make bar soap made with KOH harder. :)
 
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