Originally Posted by
cyccommute
It's the soap that cuts grease, not the glycerine.
This is misnomer. Glycerine is a component of some soaps, wherein it partly comprises the fat component (e.g., triglycerides). "Soap" is a term that describes a molecule that emulsifies water and oil/fat by an intramolecular interaction caused by a structure similar to the phospholipid of a eukaryotic cell wall (i.e., δ+ to δ- intramolecular forces) . There is no "soap molecule" - it is a categorical term.
Additionally, stomach bile salt is a great example of an emulsifier of fat/polar substances in nature, or what could be called a "natural soap." Would one use stomach bile as handsoap? Does bar soap grow on trees? Certainly not, but the blanket statement that there is no such thing as a "natural" soap is incorrect. Try searching outside of wikipedia for explanations.
Originally Posted by
cyccommute
Lye, however, is sodium hydroxide.
Lye more accurately refers to a caustic base - both KOH and NaOH fall under this category (both have low pOH), and both are used in commercial and industrial soap production, though NaOH is more common. Whether it is one or the other is a product of what the Lye is derrived from; NaOH is the product of Ca(OH)2(aq) and Na2CO3(s); KOH is typically derrived from reacting components of some ashwoods (K2CO3(s)) and Ca(OH)2(aq).