Another strong alkali?

Soapin · Mar 27, 2015

If you search Google for "soap definition" it gives you this: "a substance used with water for washing and cleaning, made of a compound of natural oils or fats with sodium hydroxide or another strong alkali, and typically having perfume and coloring added."

The FDA provides a similar definition. My question is: What is "another strong alkali" that can be used to make soap?

Thanks.

Cactuslily · Mar 27, 2015

Perhaps potassium hydroxide

Soapin · Mar 27, 2015

Thanks, Cactuslily. That was my first thought, too, but when I looked it up, potassium hydroxide is also known as lye. Is lye just a generic term for any strong alkali used in making soap?

Soapin · Mar 27, 2015

Aha, yes. I searched Google for the definition of lye, and I got "a strongly alkaline solution, especially of potassium hydroxide, used for washing or cleansing."

Merriam-Webster has two definitions of lye:

1: a strong alkaline liquor rich in potassium carbonate leached from wood ashes and used especially in making soap and for washing; broadly : a strong alkaline solution (as of sodium hydroxide or potassium hydroxide)

2: a solid caustic (as sodium hydroxide)

I've been thinking that lye was specifically sodium hydroxide, but apparently, it's any strong alkali.

Thank you!

The Efficacious Gentleman · Mar 28, 2015

As you might have seen in a thread about rendering lard and tallow recently, someone even managed to get some saponification going on using baking soda. It required added heat and was far from effective.

Other alkalis can be used, but are not as good as making soap as sodium and potassium hydroxide are

FlybyStardancer · Mar 28, 2015

Yes, there are many strong alkalies that can be used to make soap. For instance, the wood ask originally used is mostly potassium carbonate. Also, in many older recipes you'll find a mix of alkalies, including ammonia.

We generally use NaOH (for solid) and KOH (for liquid) soap because of a combination of accessibility to purer forms, relative safety, and the quality of soaps made from them.

DeeAnna · Mar 28, 2015

The old word for "lye" is "ley" or "leys". I don't know why ley morphed into the word lye, but there ya go. :???: I agree that a lot of people nowadays think lye is the same as NaOH. I suppose that's because most handcrafted soap makers are focused on sodium soap, but "lye" really can mean any strong alkali.

Although many alkali chemicals can be used to make soap, the pure alkalis we use today (NaOH or KOH) work much faster and better to saponify fat. The carbonates including the lowly baking soda can make soap, but they do it slower, they evolve carbon dioxide gas so the soap batter can foam and boil over, and the batter has to be heated to force the saponification reaction to go.

Soapin · Apr 5, 2015

Hello, everyone. I'm so sorry for my delay in responding! I tried to think of a good excuse for why it took me so long, but I found that I don't have a good excuse! Anyway, your answers are wonderful, and they all point to the same thing: Lye is a generic term used describe any strong alkali. It's funny, I've also thought badly about people putting "sodium hydroxide" on their labels instead of "lye." I thought they were trying to hide the fact that it had lye by using the chemical name instead. Now I know that sodium hydroxide or potassium hydroxide is a much more specific and accurate term than lye. So I was wrong! I learned so much through this thread. Thank you again!

Also, I looked again at my original question, and now I see that the very first answer by Cactuslily is an absolute perfect answer to what I asked. Potassium Hydroxide is indeed another strong alkali, so it totally fits! At the time, I didn't understand enough about lye to ask the right question or understand Cactuslily's answer. I was thinking that sodium dyoxide = lye, and now thanks to the rest of you, I know differently.

Thanks again!
Steven.

Another strong alkali?

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