# Making Hard Soap with Potassium Hydroxide (KOH)



## Richard Perrine

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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## amd

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.


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## Richard Perrine

amd said:


> 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.


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## DeeAnna

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


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## Richard Perrine

DeeAnna said:


> 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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## SaltedFig

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).


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## Richard Perrine

SaltedFig said:


> 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.


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## Richard Perrine

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.


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## KimT2au

My goodness, Richard, you are full of curiosity and have such an inquiring mind.  I am going to watch all your posts with interest.


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## Richard Perrine

Update. 



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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## SaltedFig

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

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).


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## Richard Perrine

Just tried a small piece of the softer bar I made which has glycerine. The citrus aroma is wonderful and the lather is generous and creamy. I hope the harder bar is like this.


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## Richard Perrine

SaltedFig said:


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


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## KimT2au

SaltedFig said:


> 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.


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## plhamp

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


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## Richard Perrine

plhamp said:


> 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.


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## Richard Perrine

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???


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## plhamp

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.


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## DeeAnna

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.


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## plhamp

> 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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## DeeAnna

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.


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## Richard Perrine

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. 




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


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## DeeAnna

_"...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

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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## cjisler

plhamp said:


> 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


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## Richard Perrine

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.


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## Zany_in_CO

KimT2au said:


> My goodness, Richard, you are full of curiosity and have such an inquiring mind.  I am going to watch all your posts with interest.


Me too!


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## earlene

So, just a point of clarity.  Both KOH and NaOH are lye, so the KOH soap is also lye soap.


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## Richard Perrine

Both KOH and NaOH are generically referred to as lye. So, yes. They are chemically similar.


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## Deb Walker

Richard Perrine said:


> 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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## Zany_in_CO

@DebWalker  How gracious of you to join us with that very useful information. Fascinating!



   and


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## Michele50

Deb Walker said:


> 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  ??


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## Deb Walker

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



Michele50 said:


> 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 ??


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## charminko.anita

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.


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## John T Erb

Richard Perrine said:


> 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.


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## atiz

John T Erb said:


> 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.


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## DeeAnna

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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## atiz

By the way, the one I have used is this one:
Instant Power Crystal Lye Drain Opener, 16 oz - Walmart.com

Pure NaOH, it worked well.


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