While I know that I touched on this in what is soap I continue to find false statements being made by so many soap makers about lye, so I felt it needed it's own seperate blog.
What is Lye? Lye is a a caustic alkaline also know as sodium hydroxide or potassium Hydroxide. It is a true base which makes it caustic to the skin in its natural state. But don't let this scare you, as it is a common ingredient in many products you use every day from soap, to glass making and even food preparation.
The most common way to get Lye (Sodium Hydroxide) is from the chlorakali process, a form of desalanization of sea water. But in the past it was created by using wood ash this created a slightly different version of Lye but it was still the same strong base, this Potassium Hydroxide can still be made at home today http://www.wikihow.com/Make-Lye.
The difference between Sodium Hydroxide and Potassium Hydroxide is the salt in each mixture that helps to create two unique forms of soap, Sodium Hydroxide is used to make bar soap while Potassium Hydroxide is used to make soft soaps.
Lye because of its alkalinity when mixed with a fat causes the chemical structure to break up and change the properties of the ingredients. The by-product is glycerin and soap.
Since glycerin is a very sought after byproduct some large companies remove it from their bar soaps and re-sell it as a single product or in the form of glycerin soap.
Lye might sound scary and while it does require extra care in it's natural form it is not dangerous or bad in a high quality soap, in fact, because of the process of saponication (the term for the chemical reaction between the fats and lye) if done correctly the Lye no longer chemically remains in the final soap.
Don't let some people scare you -- Lye is a great ingredient that has gotten a bum wrap. Also know that without it you can not have soap, instead you only have a detergent bar. Now enjoy some homemade, well crafted soap in the knowledge that this great product is a part of our history.