I think it is important for you, as a lover of homemade bath products, to understand some of the most important (and maybe some of the not so important) ingredients used. As cold processed soap is my primary product, we should first discuss Sodium Hydroxide, better known as LYE because if you don’t have lye, you don’t have true soap. 

Through the years, lye has had many uses — from cleaning to making pretzels, bagels, and even hominy. In past years, lye was touted in many advertisements in the early 20th century. Check out this pamphlet from 1914 that is singing the praises of lye in the household. Now understand that the lye in these ads is probably not as pure as the lye we can get today. The lye I purchase is 98% to 99.9% pure. The impurities, of course, would make it weaker. Besides , today we have much better and safer household cleaners than lye water.

To discuss lye in soap making, we will have to discuss saponification.  Simply put, saponification is the chemical reaction that occurs during the process of mixing lye with oils to form a salt which we call soap.  Glycerin is an important byproduct of the saponification process and is in all “lye” soap even though it is not listed in the ingredients.  We will be discussing glycerin at another time.

Combining oils (olive, sweet almond, coconut, palm, lard, tallow, etc.) with lye is the beginning of all soap.  That’s the simple truth of it.  All SOAP is made with lye.  Yes, even the glycerin soap (melt and pour) that is true soap begins with lye. If there is no lye, there is no soap.  You have a detergent.

Now, understand that Sodium Hydroxide, or lye, by itself is a very caustic substance that can cause serious damage. For this reason, when handling it, one should always take the precautions of wearing gloves, safety glasses, and masks as lye can burn your skin and your mucous membranes if mishandled. When lye is added to oil, vegetable or animal, and is allowed to cure, it produces a “salt” we call soap with the byproduct we call glycerin.

Every oil has an SAP (short for saponification) number. The SAP number is the units of lye (ounces, grams, etc.) needed to completely react with one unit (ounces, grams, etc.) of a certain oil.  Every oil is different.  By using these numbers, the soapmaker can determine the amount of lye needed for any recipe. 

But when we think of lye soap we think of the harsh stuff Grandma (or now Great-grandma) used to make in the back yard.  It was a long, arduous process that required lots of patience (and stirring and stirring and stirring).  Because Grandma couldn’t generally go to the hardware store to buy lye, she had to start with ashes and make her lye to make her soap. This lye would not be pure; and each time, the process would yield a somewhat different product which would ultimately cause variations in her final soap. She also didn’t have the saponification specs for each oil (although she would have used only lard or tallow), so she made soap the way her mom had taught her.  Sometimes she would come out with very harsh, lye-heavy soap that was irritating to the skin.  You wouldn’t want use it to bathe every day.  Luckily they only bathed once a week or less.

Today it its easy to access the SAP ratios for each oil online or in books.  We use these numbers to determine how much lye to use, and then we generally “superfat” our soaps.  This just means that we add more oils (or less lye) than we need so that our skin benefits from the oils left in the bar.