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Melt and Pour Soap makers have a similar line, "Commercial soaps remove the glycerine for use in more profit producing lotions and creams, my soap has extra glycerine added to it. This helps make it clear, and also makes it a lot more moisturizing."
But what is glycerine, really?
Glycerin is a neutral, sweet-tasting, colourless, thick liquid which freezes to a gummy paste and which has a high boiling point. Glycerin can be dissolved into water or alcohol, but not oils. On the other hand, many things will dissolve into glycerine easier than they do into water or alcohol. So it is a good solvent.
Glycerin is also highly "hygroscopic" which means that it absorbs water from the air. Example: if you left a bottle of pure glycerine exposed to air in your kitchen, it would take moisture from the air and eventually, it would become 80 per glycerine and 20 percent water.
Because of this hygroscopic quality, pure, 100 percent glycerine placed on the tongue may raise a blister, since it is dehydrating. Diluted with water, however, it will soften your skin. (Note: While people say this softening is the result of the glycerine attracting moisture to your skin, there is heated debate as to whether or not the glycerine has some other properties all its own which are helpful to the skin. Summed up, the current thinking is "We know glycerine softens the skin. Some people think its because it attracts moisture, but there could be other reasons.")
Where does glycerine come from?
Up until 1889, people didn't know how to recover glycerine from the soap making process, so commercially produced glycerine mostly came from the candle making industry (remember, back then candles were made from animal fats).
In 1889, a viable way to separate the glycerine out of the soap was finally implemented. Since the number one use of glycerine was to make nitro-glycerine, 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 glycerine 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 glycerine 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 glycerine is left out as a "by-product". 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 moulds 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 glycerine (and lots of "impurities" like partially dissolved soap, extra salt, etc.). They then separate the glycerine out by distilling it. Finally, they de-colorize the glycerine by filtering it through charcoal, or by using some other bleaching method.
Glycerin has lots of uses besides being used to make nitro-glycerine (note: glycerine is not an explosive substance by itself. It has to be turned into nitro-glycerine before it becomes explosive, so it's safe to work with in your kitchen). Some uses for glycerine include: conserving preserved fruit, as a base for lotions, to prevent freezing in hydraulic jacks, to lubricate moulds, 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 glycerine. 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 glycerine content, the soaps are very moisturizing to the skin. Unfortunately, this high glycerine content also means that the soaps will dissolve more rapidly in water than soaps with less glycerine, 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.
- © Copyright, 1997, Kaila Westerman