Making Hard Soap with Potassium Hydroxide (KOH)

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DeeAnna

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By adding table salt, some of the potassium soap will be converted into sodium soap as well as playing with the solubility of soap in a brine (table salt solution.) If a person's goal is to make a pure potassium soap, it's kind of counterproductive to use table salt. The chemist type in me wants to point that out for those who might not know.

But I realize you are just using up stuff you already have and having fun exploring this aspect of soapmaking. S'all good.

I followed the link above to the Natural Soap article. It says this at the end -- "...To make your own Potassium Hydroxide, or potash you collect ashes and percolate water through them and collect it...."

Lye made from wood ashes is mostly potassium carbonate with perhaps some sodium carbonate depending on the type of plant material used. The common name given is incorrect. Potassium hydroxide is caustic potash. Potassium carbonate is just potash.
 

Richard Perrine

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Update.
My family has been testing out my KOH soap bars and they have been a hit. Not too certain of the overall benefits yet or how they feel different from my regular lye soaps, but the lower pH must be something. I would like to think that the lower pH means less harsh soap, right? The bars are holding up in the showers and the fragrances/EOs also seem to be holding.

IMG_4407.JPG
Vanilla Oak. Nice fragrance and unmoulding was very similar to CP-Lye soap. Firm.
 

DeeAnna

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"...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???)..."

KOH soap doesn't have a greatly different pH range than NaOH soap does. I'm not quite sure how you are getting these pH numbers, because they're honestly unrealistic. A true pH of 8 or less is not going to happen in a lye-based soap, no matter what alkali you use.

People often report pH numbers that are too low all the time, but that doesn't mean their soap really has that pH. It's very easy to get an incorrect pH reading for soap if you don't use good equipment and the right technique.

Mildness is not simply determined by the pH of soap -- or any other type of cleanser. The solubility of the soap, the relative proportions of the fatty acids present, the amount of soap present on the skin, the superfat, the person using the soap, etc. all affect whether a soap is perceived as mild or not.
 
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Richard Perrine

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DeeAnna. One thing is for certain, relatively speaking, the KOH bars are showing a lower pH compared to my lye soaps. I am using pH strips and when comparing the colours for the pH, there is a discernible difference. I agree that the pH is likely not that accurate, but in relative terms, there is a difference. I have purchased a pH indicator that seems to be more accurate. We'll see...
 
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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

Yes. My mother said that was how her grandmother made soap, too. Carol
 

Richard Perrine

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I looked back at my most recent response and need to clarify that the pH difference is after 2-3 days of curing.

I also pulled out my rarely used mortar and pestle and finely ground the salt to powder. Better dispersion and dissolution.
 

Deb Walker

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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.

Hi, I saw your post so joined so I can give you some info. I did a lot of searching for KOH hard bar soap in the past and ended up testing some things. I have been making very nice hard bar soap simply by adding 20% salt.
Because the hardness is not so dependent on solid oils, you can make a very gentle bar. Not super bubbly but a good cream and satisfactory bubbles.
Friends have had very good results with stubborn dermatitis/skin infection type issues and have not found it drying.
I dissolve as much salt as I can in the water before dissolving the lye and the rest I just add to the oils. The only negative thing about this soap is that I live in the subtropics and the high humidity in summer makes the soap sweat badly if I make it in summer. I just make my years supply in late winter when it is very dry and the soap can cure. When it is well dried, I bag in a zip lock bag.
Based on what thickens liquid KOH soap I would recommend:
Not using higher percentages of Coconut oil (not over 15%) or Castor oil .
Not using citrus essential oils. There are some essential oils that don't effect the thickening of liquid soap (with salt) when used singly but do when blended with certain other essential oils.
I think it is possible that using borax will also make a hard bar.
Hope this is useful.
 
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Hi, I saw your post so joined so I can give you some info. I did a lot of searching for KOH hard bar soap in the past and ended up testing some things. I have been making very nice hard bar soap simply by adding 20% salt.
Because the hardness is not so dependent on solid oils, you can make a very gentle bar. Not super bubbly but a good cream and satisfactory bubbles.
Friends have had very good results with stubborn dermatitis/skin infection type issues and have not found it drying.
I dissolve as much salt as I can in the water before dissolving the lye and the rest I just add to the oils. The only negative thing about this soap is that I live in the subtropics and the high humidity in summer makes the soap sweat badly if I make it in summer. I just make my years supply in late winter when it is very dry and the soap can cure. When it is well dried, I bag in a zip lock bag.
Based on what thickens liquid KOH soap I would recommend:
Not using higher percentages of Coconut oil (not over 15%) or Castor oil .
Not using citrus essential oils. There are some essential oils that don't effect the thickening of liquid soap (with salt) when used singly but do when blended with certain other essential oils.
I think it is possible that using borax will also make a hard bar.
Hope this is useful.
I told you that I had happened across someone who made soap' bars' using KOH and this is the one it was.....I think. I'm guessing that you guys hot process and that you don't cook it down to that hard paste, is that correct @Deb Walker ??
 

Deb Walker

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Hi Michele,
Yes that's me :).
I just put my recipe (nothing special) into soapcalc and put it onto KOH lye. Its not so important to get the hardness because the salt does that. Because of this you can make a far more gentle cleansing bar and this is the quality that I have read is sort after in KOH bars. I'm not so taken by high Olive oil NaOH (Castile) bars so this is suitable for me.
No I don't cook it. Heat curdled the batter once and I had to put the whole pot in cold water and it came good with stirring.
I dissolve probably half of the salt in the water before I dissolve the lye and the rest goes in the oil. Whether this is better or worse than anything else, I don't know. I wanted the brine so it would really mix in well.

I haven't done much experimenting with this because I was happy with it.
Happy soaping

I told you that I had happened across someone who made soap' bars' using KOH and this is the one it was.....I think. I'm guessing that you guys hot process and that you don't cook it down to that hard paste, is that correct @Deb Walker ??
 

charminko.anita

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hi
i am a beginner soaper and also have been playing with ashes to make potassium hydroxide soap.Because I am using potassium hydroxide I made from ashes it is hard to make accurate measurements but I mixed what I believe to be about 50% sodium hydroxide to my recipe.It turned out soft like play dough and is still drying.I then added a small amount of stearic acid to my next batch and it came out much harder.This batch is still drying but I think I will be getting a good shaving bar.
 

John T Erb

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Both KOH and NaOH are generically referred to as lye. So, yes. They are chemically similar.
I'm a beginner at soaping and have yet to pull the trigger on my first batch. I also work at Walmart and noticed recently that we sell a drain cleaner in our hardware department that is a combination of sodium hydroxide and potassium hydroxide. I was wondering if this would be usable in soap-making. The ratio isn't listed.
 

atiz

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I'm a beginner at soaping and have yet to pull the trigger on my first batch. I also work at Walmart and noticed recently that we sell a drain cleaner in our hardware department that is a combination of sodium hydroxide and potassium hydroxide. I was wondering if this would be usable in soap-making. The ratio isn't listed.
Not Richard... But you would likely want to know the NaOH/KOH ratio, otherwise it will be difficult to calculate how much you need.
FWIW, when I started soaping, I got my lye from Walmart -- there was a drain cleaner that was pure NaOH, in the plumbing section. Unfortunately I can't remember the brand.
 

DeeAnna

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If the drain cleaner is a liquid mixture, it's my guess the solution won't be concentrated enough for making soap. We're working with concentrations of at least 25% alkali, and often a lot higher. Drain cleaner doesn't need to be nearly that concentrated to work correctly. One liquid drain cleaner I looked at was about 15% alkali with the rest being water.

If it's a solid mixture, what Atiz said is the key -- you will have to know the ratio between the two alkalis. A lot more weight of KOH is required to get the same result that you'd get with NaOH. Like if a recipe needs 100 grams NaOH to saponify, it will require 140 grams of KOH. Big difference. Also you'd want to confirm the mixture is 100% alkali -- no fillers.

I'd also worry about consistency of a dry mix. Is there more KOH at the bottom of the container and more NaOH at the top? Or vice versa? Any variation would not make much difference if it's used as a drain cleaner, but it could make a big difference when used to make soap.
 
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