Glycerin is a neutral,
sweet-tasting, colorless, thick liquid which freezes to a gummy paste and which
has a high boiling point. It can be dissolved into water or alcohol, but
not oils. On the other hand, many things will dissolve into glycerin easier than
they do into water or alcohol. So it is a good solvent.
Glycerin is also highly
"hydroscopic" which means that it absorbs water from the air. Example:
if you left a bottle of pure glycerin exposed to air in your kitchen, it would
take moisture from the air and eventually, it would become 80 per glycerin and
20 percent water.
Because of this hydroscopic
quality, pure, 100 percent glycerin 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 glycerin attracting
moisture to your skin, there is heated debate as to whether or not the glycerin
has some other properties all its own which are helpful to the skin. Summed up,
the current thinking is "We know glycerin softens the skin. Some people
think its because it attracts moisture, but there could be other reasons.")
Where does glycerin come from?
Very simply, it comes from fats, and is generally a byproduct of
soap-making. Up until 1889, people didn't
know how to recover glycerin from the soap-making process, so commercially
produced glycerin mostly came from the candle-making industry (back
then candles were made from animal fats).
In 1889, a viable way to
separate the glycerin out of 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!
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% glycerin). 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). 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.
In as much as glycerin is
derived from fat, and that it is often derived from animal fat - among the most
common of these being pork, there are some obvious concerns with Glycerin.
Generally, it is understood that vegetable glycerin is fine; however, one must
determine what methods were used to bleach the glycerin (if it was bleached) in
order to determine whether or not it is permissible. All other forms of
glycerin in food, soap or other products are prohibited.