As a professional soap maker you should know how to manually calculate the saponification value of potassium hydroxide (KOH) over to sodium hydroxide (NaOH). You may find the sodium hydroxide value of a soap making oil from the oil specification sheet. This sheet is provided to you from the supplier where you purchase your soap making oils from. Most likely the sodium hydroxide (NaOH) value won’t be reported but the potassium hydroxide (KOH) value. Now if you are working potassium hydroxide that will be grand. But what if you are not.
Oil Specification Sheet
So how do you convert the potassium hydroxide SAP value to the sodium hydroxide SAP value? You take the potassium hydroxide value and divide it by 1.403. It’s that simple.
For example, in the image of an oil specification sheet you see the potassium hydroxide saponification value is 194. Take the 194 and divide it by 1.403. The end result will be 138.
So why do we need to know this number anyway? Well, you need to know the
correct saponification value for the correct lye that you are working with to make the type of soap you are making so that you can know how much lye will you need to convert the soap making oils into soap.
If you want hard bar soap you will need to use sodium hydroxide and if you are making liquid soap you will need potassium hydroxide.
In the example above the cocoa butters sodium hydroxide SAP value is 138. If we were going to use ten ounces of cocoa butter. We would multiply the ten ounces of cocoa butter by .138. Which will give the result of 1.38 ounces of sodium hydroxide to saponify the ten ounces of cocoa butter. Please notice that I put a decimal point in front of the 138. This is a necessary step. If you don’t you will be using way too much lye.
Now you know how to convert the saponification value of potassium hydroxide to sodium hydroxide. You never know this might be a final Jeopardy question.