soaping terms

Soap making is chemistry in action -- and because it's chemistry, it can be confusing. Below, for the curious, some definitions.

fatty acid + strong base = soap + glycerin

Cure Time

The reason you have to wait weeks and weeks and weeks

to buy & use the delicious, freshly made soap you know has been made, but isn't yet available for purchase.


The name given to the chemical reaction between fatty acid (fixed oils) and strong base (lye) that produces soap (a salt) and glycerin. When acid and base have merged on a molecular level, neither ingredient remains; the atomic binding of oil and lye creates an entirely new substance -- soap, which is chemically a "salt of fatty acids." Bonded in this way, oils and lye are said to have saponified. Saponification takes 24-48 hours when a cold process soap making method is used (no external heat is applied.) When soap is hot processed (heated by an external source like a crockpot or stovetop) saponification occurs faster, in minutes to hours.

Cure time

The period of time following saponification during which water evaporates from soap, hardening and "maturing" it. Water is used in soap making as a solvent; its sole purpose is to dissolve lye so it will interact with oils, creating soap. The cure time for a given soap depends on a variety of factors including specific ingredients; the water:lye ratio; humidity of the curing environment; ambient temperature; and more. Generally, soaps cure in 3-6 weeks.

Fixed oils

Also known as carrier oils, fixed oils are typically extracted from the nut or seed of a plant. These fatty acids are called "fixed" oils because they contain large molecules that do not easily evaporate (like volatile essential oils do.) A few fixed oils common to soap making are: olive, coconut, avocado, rice bran, castor, and sweet almond, among many others.


Also known as sodium hydroxide (NaOH), lye is the strong base (alkali) necessary for soap creation. It's not possible to make true soap without lye, because nothing else will turn oils into soap. The lye in a soap recipe is entirely consumed  by the saponification reaction; it merges atomically with fixed oils to form soap molecules. Historically, lye was made by boiling wood ash, then skimming the lye water off the top. Nowadays, lye is made by mingling salt with water and electricity until lye crystals form. Used properly, lye is 100% safe -- it's even used to cure foods like olives, canned mandarins, and pretzels!



A soap is superfatted when the measure of fats (oils and butters, like olive or shea) is more than what is required for the saponification reaction to occur. These "leftover" oils contribute to soap's skin-loving properties.


An "alkali salt of a fatty acid," soap is the substance that results when fats (acids) combine with a base (alkali) solution to produce soap (a surfectant) and glycerin.


A substance which reduces the surface tension between two other substances, allowing them to be separated. As a surfectant, soap separates dirt from body oils and suspends it in water, which allows it to be washed away.


A synthetic, lab created, artificial surfectant that cleanses, but is not soap. Made from petroleum by-products and often containing antibacterial agents and preservatives, detergents are less biodegradable than soap (read: worse for the environment.) Despite these drawbacks, there is a place for detergents: because of their strength, they do a better job than soap of cleaning oily dirt, especially on textured surfaces like fabrics or greasy surfaces like dishes and pots. That same strength makes detergents much harsher than soap on skin, however, stripping beneficial and protective oils, and causing irritation, excessive tightness and drying, and even allergic response in those with sensitive skin.


Present in all fats (vegetable or animal), glycerin is an endogenous humectant, meaning it's one of the moisturizing compounds that can be found on our skin naturally.


A substance that draws and retains moisture.


Chemical compounds derived from petroleum -- a natural, usually black, viscous liquid found in rock formations beneath the surface of the Earth. Petroleum is commonly refined into fuels including gasoline, kerosene, and diesel oil.


A state in which matter is thick, sticky, and semi-fluid.


A substance that improves personal appearance or aroma (as defined by the FDA.)


When a mixture of two liquids that can't be completely blended together (like water and oil) are as mixed as they can get.


The point in the soap making process when oils and lye water have emulsified.