Soap is the product of saponifcation. Saponification is the process whereby the fatty acits in oil interact with an alkali to produce what is called "salt of fatty acid" - or more popularly known as SOAP.
There are two kind of alkali (or "lye") used in soapmaking. One is Sodium Hydroxide (also called caustic soda). This is the lye used when making solid soaps. The other kind of lye is Potassium Hydroxide (also called caustic potash). This is the lye used in making liquid soaps.
Soap is the product of the interaction of oil and alkali. Oil is composed of fatty acids and glycerol, while alkali (in case of solid soaps) is composed of sodium, oxygen and hydrogen molecules (or NaOH). When oil and alkali interact, the fatty acids in the oil cling to the sodium, the oxygen and the hydrogen molecules, thus creating the "salt of fatty acid" or soap.
What happens to the glycerol? Well, the glycerol is separated from the fatty acid but remains as part of the soap that has been created. It is the presence of glycerol (or glycerin) that is responsible for the soap's moisturizing effect.
However, some manufacturers remove the glycerol from the soap and sell glycerin by itself. This glycerin is the one that is then made into blocks and sold as part of melt-and-pour kits.
That is why glycerin soaps cannot be considered soaps in the technical sense. The only things we can truly call "soaps" are those that are created as a result of the interaction between fatty acids and an alkali, otherwise known as saponification.Did you find the foregoing information useful? If you did, join our email list and receive useful and practical information on a regular basis. Click here to join.