Three years ago, trying to find a way to have liquid soap without the plastic bottle, I discovered that you can’t actually make real liquid soap from a solid soap bar. What I ended up with was a slimy green failure. And the reason is that liquid and solid soaps have different chemistries. The lye used to make solid soap is sodium hydroxide; whereas, the lye used to make liquid soap is potassium hydroxide. According to Wikipedia:
The saponification of fats with KOH [potassium hydroxide] is used to prepare the corresponding “potassium soaps”, which are softer than the more common sodium hydroxide-derived soaps. Because of their softness and greater solubility, potassium soaps require less water to liquefy, and can thus contain more cleaning agent than liquefied sodium soaps
So for the past 4 years, I’ve been doing without any kind of liquid soap. But recently, attempting to deal with some fungus problems in my garden, I’ve come across several recipes for treatments that require liquid dish soap, and not having any, I decided to try once again to make liquid soap out of solid soap. I found some actual instructions on the Internet for doing just that, and I realized there were a few mistakes I made the first time around. The ratio of soap to water was way off, and my method of dissolving the soap was just insane. I also think I chose the wrong kind of bar soap to start out with.
You Can (Sort of) Make Liquid Soap From Bar Soap
For what it’s worth, here are the best instructions I can come up with for making a pseudo liquid soap out of bar soap. It’s not perfect. The end result is slimier than real liquid soap, but it works for my purposes and maybe would work for you as well.
Ingredients: 4 ounces of solid natural soap, 1 gallon of water, cheese grater, big steel pot, and an electric mixer (not essential but helps.)
Look at the proportion of soap to water. In my previous attempt, I dissolved an entire 1,000 gram block of solid olive oil soap in a pot of water. That’s about 9 times as much soap as I should have used. No wonder I ended up with a pot of solid soap after the mixture cooled.
This time, I chose a 3.55 ounce bar of Sappo Hill aloe vera soap made with palm oil, coconut oil, and glycerin. I thought maybe these ingredients would make a smoother, less slimy liquid soap than the olive oil had. Also, it’s what I had in the house. Sappo Hill soaps are sold naked without packaging — plastic or otherwise.
(I also reduced the water by 25% since I used less than 4 ounces of soap.)
1) Grate the solid soap. This is an important step to a well-mixed result. The last time, I just stuck the whole block of soap in a pot of water on the stove and waited forever for it to dissolve.
2) Bring water to a boil in steel pot and remove from stove. Pour grated soap into pot and stir until dissolved.
3) Let sit over night.
The next day, the soap had somewhat solidified into a thick jelly. It was kind of slimy, but definitely not solid. I could have stopped at this point and used it as is.
4) Blend with a hand mixer.
This step ensures the soap is mixed well but it also adds air to fluff it up and make it less like something that came out of your nose the last time you had the flu.
The result is quite nice, if not exactly Dr. Bronner’s.
5) Bottle it in a glass jug or a secondhand pump bottle.
Do keep in mind, per the Wikipedia entry above, that this soap is less concentrated than real liquid soap, so when using it in recipes, you will probably have to use more than is called for.