Wednesday, 24 February 2016

Potassium Hydroxide Bar Soap

I have searched for recipe's for bar soap made from KOH with little sucess.  I found a French site that claimed success with salt but refused to share their recipe details.  It was stated to be very gentle on the skin. Another was a survival web site and they used Borax and Ammonia but this was complicated and I'm not using those ingredients for soap. Others say you can only use animal fat.

I based my process on historic accounts of soap making (though they had no recipes) and the principles of thickening liquid soap

The key ingredient is salt. Because higher levels of Coconut oil and castor oil in liquid soap wont allow it to thicken with salt I kept these two ingredient quantities low.  I knew Beef Tallow or Lard was used in the past so would work,  Olive Oil as this thickens very well with salt in liquid soap so am confident with this.  I have read that Shea Butter has been used. I had also read that salt should be 20% of the oil weight.

My first attempt worked very well and you can read about thiat but I have simplified this recipe and process and it is working really well.

Palm Oil          760gm
Coconut Oil     120gm
Castor Oil         120gm
Potassium Hydroxide  224gm (gives a 1% Super Fat)
Water                           380gm
Himalayan Salt            150gm  (fine ground)
30gm Oil of your choice added at trace to increase the super fat to 4%
32gm Essential Oil for fragrance and health benefits.

I dissolve the salt in the water prior to adding the lye.  Some of the salt will not dissolve but I like this as a salt bar.  This has a salt level of 16% but you could try lowering it, but I don't know how low you can go. Just make sure the lye is stirred really well.  It is not a drying soap.

I advise wearing a dust mask as well as safety glasses and gloves as the Potash is a bit dusty.  This is easily breathed in.

Very easy to make and handles well. After a day or two the pH drops nice and low. Nice bubbles,  very creamy and a gentle cleaner.  A favourite to make and use.

If altering the recipe be mindful that soap with higher levels of Coconut oil and Castor oil do not thicken with salt.  I am not exactly sure of the percentage but it is not much higher than I have used here.

In hot weather I have had the batter curdle on me as I mixed it and also after it was poured in the mould.  The reason for this is heat of the batter.  Best solution is to sit your pot of soap batter in a basin of cold water (I added ice packs). As it cooled it thickened up nicely. I now sit my moulds on ice packs just to prevent this happening in the mould.

An alternative recipe with Beef Tallow
Beef Tallow              660gm
Olive Oil                   100gm  (to increase the conditioning level)
Coconut oil                120gm
Castor oil                   120gm
Potash                       217gm  (gives a 4% super fat)
Water                         380gm
Himalayan Salt        150gm

My First Potash Soap.
When I turned the solid KOH soap from the mould it was pH 7ish on litmus paper.  It was firm but spongy to squeeze, not soft.  It sliced well and was a pale yellow/creamy colour.
Hard Potash / Potassium Hydroxide Bar Soap

 Because the pH was so low at the early stage I used some trimmings to test washing my hands.  It didn't feel like NaOH uncured soap (slimy).

It has a mottled whitish effect which was not undissolved lye, but salt as much of it didn't dissolve in the water prior to adding to the oils.  Small salt granules catching the light. The zap test was good and had a pleasant enough taste.

If you use Hymalayan salt you will benefit from the minerals that are removed from refined salt. You also don't get the anti-caking agent in refined salt (and what ever else they put in it). I would dissolve the lye in the water before adding the salt as a lot of the salt wont dissolve and I like to see that the lye is dissolved.

It came to trace quite quickly but there was no panic to get it into the mould.  It didn't heat up as much as Na OH soap and didn't go through a gel phase even though I had covered it with a towel.

The cost of the salt is offset by the very cheap price I paid for a big bag of Potassium Hydroxide from a pool chemical outlet.

You can make your own Potassium Hydroxide (Potash) running water through ashes. There are web sites that show how to do this.

3 Weeks Later
I used this from the second day to test because of the very low pH (in the 7 range) and it was very easy on my skin and tolerated water well right from then.
The hardness rating on SoapCalc is not relevant.  It starts off a bit sponginy but hardens up beyond the rate given on SOapCalc.  The yellow colour has faded to a very white in colour.  The lather is creamy and lightly bubbling.   I'm very happy with the very creamy feel of it.  It is moist to touch with humid weather.  In spite of this it is not slimy or messy. For a mild and gentle soap I would rather have this than Castile soap (80% Olive Oil) because the salt bar doesn't leave such a mess when wet.  There is no scratchiness though there are some salt crystals

Conclusion 6 months later
I have given some bars to friends for testing.  One told me that at first she thought it was drying but then she noticed that the dermatitis she had always suffered was clearing up.  When it was gone, the skin looked good.  No dermatitis and no dryness. No one I have given them too has reported drying.

This is being reported by friends as their favourite of the soaps I make including goat milk soap with very good results for skin conditions.  This is far less complicated than making a milk soap.

I am thinking that it will be good for acne and skin infections. I am very happy with this soap.

Brine Bar:  This is where all the salt is dissolved in the recipe water.  A salt bar has crystals.
Some people add the salt at trace to keep the crystals when using NaOH but at the moment I am more confident dissolving as much as possible in the water as I am reliant on the salt to thicken.

Making your own Potassium Hydroxide.
To make your own Potassium Hydroxide, or potash you collect ashes and percolate water through them and collect it.  Wooden hoppers were traditionally used and lined with straw for a filter and the ash put on top.

This water will be very alkaline and damaging to your skin.  In history, this water was concentrated by evaporation till a feather could dissolve and a fresh egg would float so it sat half in the water.  I do not have the quantities that should be used.

One day I plan to try this.  At the moment I think the best way to work out the quantity is to get an accurate measurement of the pH of the lye water used from my "pool chemical" NaOH, then use the same amount of water at the same pH from ashes.

Other variations of KOH soap are:
Black African Soap and Gray Polish Soap both of which are prized for their gentle cleaning characteristic.


  1. thank you very much. I will try to make this soap this year. If I make changes to your recipe, I will let you know of the results. :-)

  2. Thanks a ton for this recipe! Can't use beef tallow! Palm oil unavailable! Since I live in South india, I had to substitute palm oil with palmolein oil. Soap came out just great! But started Watering during the rainy season ... Plz help!

    1. Hi Niveditha,
      Natural soap will attract moisture in high humidity - it is the sign of a good soap. Also with the added salt this may be worse. This happens to me here in our subtropical climate sometimes too. All I can suggest is to store the unused soap in a sealed container with something like a paper towel (soft paper) to absorb some moisture. All the best.
      I was in India in January...and took some soap for friends who don't have much. Amazing place.