Up until 1889, people didn’t know how to recover glycerine from the soap-making process, so commercially produced glycerin mostly came from the candle-making industry (remember, back then candles were made from animal fats).
In 1889, a viable way to separate the glycerin out of the soap was finally implemented. Since the number one use of glycerin was to make nitroglycerin, which was used to make dynamite, making soap suddenly became a lot more profitable! I have an untested theory that you could trace the roots of most big soap-makers (and the “fall” of the small, local soap-maker) to about this time in history.
The process of removing the glycerin from the soap is fairly complicated (and of course, there are a lot of variations on the theme). In the most simplest terms: you make soap out of fats and lye. The fats already contain glycerin as part of their chemical makeup (both animal and vegetable fats contain from 7% – 13% glycerine). When the fats and lye interact, soap is formed, and the glycerin is left out as a “byproduct”. But, while it’s chemically separate, it’s still blended into the soap mix.
While a cold process soap-maker would simply pour into the molds at this stage, a commercial soap-maker will add salt. The salt causes the soap to curdle and float to the top. After skimming off the soap, they are left with glycerin (and lots of “impurities” like partially dissolved soap, extra salt, etc.). They then separate the glycerin out by distilling it. Finally, they de-colorize the glycerin by filtering it through charcoal, or by using some other bleaching method.
Glycerin has lots of uses besides being used to make nitroglycerin (note: glycerin is not an explosive substance by itself. It has to be turned into nitroglycerin before it becomes explosive, so it’s safe to work with in your kitchen). Some uses for glycerin include: conserving preserved fruit, as a base for lotions, to prevent freezing in hydraulic jacks, to lubricate molds, in some printing inks, in cake and candy making, and (because it has an antiseptic quality) sometimes to preserve scientific specimens in jars in your high school biology lab.
Glycerin is also used to make clear soaps. Highly glycerinated clear soaps contain about 15% – 20% pure glycerin. Known as “Melt and Pour” soaps, these soaps are very easy for the hobbyist to work with. They melt at about 160 degrees Fahrenheit, and solidify fairly rapidly. Because of their high glycerin content, the soaps are very moisturizing to the skin. Unfortunately, this high glycerin content also means that the soaps will dissolve more rapidly in water than soaps with less glycerin, and that if the bar of soap is left exposed to air, it will attract moisture and “glisten” with beads of ambient moisture.
These downsides, however are more than compensated by the emollient, skin loving and gentle nature of this soap which is especially good for tender skin and children.
(1) The pure chemical product is called Glycerol (which shows that it is an alcohol), while the impure commercial product is called Glycerin. This is a technical complexity, so for this article, I’m sticking to the more familiar term, Glycerin.
