What is Soap?
Soap is what you get when an Oil (fatty acids) is blended with Lye (Hydroxide of Sodium or Potassium) and water, and undergoes a process called Saponification. Any lathering agent that does not follow this process, is not soap.
The process of saponification also gives glycerine as a by product. This means that all soap has glycerine in it, unless chemically extracted from it.
Different naturally occurring plant and animal based oils and fats differ in their fatty acid compositions. They also behave in a unique manner upon saponification. The quality of soap depends on the selection of oils and their ratios.
A handcrafted soap brings to you a carefully composed mix of saponified oils, along with some percentage of free oils, known as Superfat, that provide an added boost of conditioning to the skin. This composition is a delicate balance which can get enhanced, or completely ruined when mixed with extra additives and fragrances.
The 3-Oil recipe
The basic bath soap is expected to have three main qualities. First, it should lather, second, it should condition and not be too drying, and third, it should not dissolve too fast. Coconut oil, Olive oil and Palm oil together make a superb 3-oil soap.
Add to that a choice of clays, herbs, fragrances, essential oils, spices and other additives and Viola! you have a large buffet of gorgeous soap.
The Single oil soap
Soap made from Olive oil alone, also called Castile soap, produces little to no bubbles and has extremely mild cleansing properties. The lather is slimy in texture and is conditioning to the skin. Castile soap is considered ideal for babies.
The luxury soap
Rich oils and butters in the main recipe makes a highly conditioning recipe. An oily soap typically doesn't produce fluffy lather and is also the least drying.