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What is Green Soap?
Soaps were traditionally made from animal fats (also
known as Tallow). These soaps are usually white or cream colored and often firm. Green soap, however, is made from plant
oils and its green color is the result of the types of plant oils used.
"Castile Soaps" were historically made from plant ash (a source of lye,
particularly from hardwoods) and olive oil. Now any soap that uses its fat source as olive oil can be called a "Castile Soap." The Green soap that most
tattoo artists are familiar with is the Cosco Green Soap, made in
America since 1966.
The
Cosco Green Soap is often called a "Tincture" of Green Soap. Tinctures
are
alcoholic extracts of substances such as plant materials and by
definition have a high
percentage of alcohol.
The alcohol in Green Soap acts as a disinfectant. This contrasts with
Dettol, which uses Chloroxylenol as a biocide (literally translated
"life-killer"). Chloroxylenol is toxic to bacteria but has low toxicity
to humans but is highly toxic to fish. It is not a "green" product
(both literally and figuratively) since it uses chemical antiseptics.
Frankly, we like the natural and less fish-murderous ways of Green Soap
over Dettol, but this is simply a matter of preference. We use Green
Soap in the tattoo world to clean the skin prior to application of a
stencil or tattooing, and also as an all-purpose instrument cleanser
prior to
sterilization. It really is great stuff!
The rest of this article goes into greater detail about soap chemistry, so if that isn't your cup of tea, stop reading now!
How do you make soap?To answer this question, we need to first ask simply "What is soap?" Forgive me, but
this requires a little bit of organic chemistry. Don't feel bad if it takes you a couple of reads. This stuff is designed to weed out prospective medical students!
Organic Chemistry 101
Oil and Water Doesn't Mix!
In organic chemistry, one of the first dictums we learned as students is "like dissolves like" or more simply, oil doesn't dissolve in water. Oil-loving compounds (like grease) dissolve in oil, and water-loving compounds (molecules with charges) dissolve in water. The reason for this has to do with "hydrogen bonding," but the practical application of this is that you can't just wash the grease off your hands with plain water. The trick then, is to find something that will act as an interface between oil and water so that you can dissolve a greasy substance into water. Soap is that substance!
Crash Course in Organic Chemistry
Carbon is the backbone of organic chemistry and of all living things. We build
molecules out of carbon in all kinds of interesting ways. You'll see the carbon atoms
represented as the letter 'C', hydrogen atoms as 'H', and oxygen atoms as 'O'. When we have a whole bunch of carbons all in a row, rather than to keep
writing the letter 'C', we simply draw a twisty line with each kink
point in the line representing a carbon atom. When
we join oxygen with a single hydrogen the resulting 'OH' is an alcohol.
How do I make soap?
We start out with fat. Fat is also known as triglyceride. Triglycerides are compounds that consist of a glycerol molecule (also called glycerin or glycerine) joined to three "fatty acid" molecules.
Example chemical structure of triglyceride
If we add a strong alkali (the opposite of an acid) such as sodium hydroxide (the
active ingredient in most drain cleaners), we can break triglycerides apart into their
base components of glycerin and fatty acids in a process known as "saponification".
Example of Saponification: Triglyceride is broken down by sodium hydroxide (NaOH) in water to produce free fatty acids and glycerol. Technically, these fatty acids are no longer an acid, but rather their conjugate base, in the form of a salt.Glycerol is simply a three carbon alcohol (alcohols possess an -OH group). The other components of triglyceride are the fatty acids. Fatty acids are simply linear
chains of carbons with a carboxylic acid group on the end.
In organic chemistry, various compounds are given common names. This fatty acid goes by the common name of Palmitic Acid (or its salt, Palmitate).
Structure of Palmitic Acid, a type of fatty acid. Note the long carbon chain.
It gets
that name because it is extracted from the natural oil found in Palm Trees. It is a
widely used fatty acid in the detergent-making world. By now you are wondering if it
is used in Palmolive soap and the answer is YES! It also has a more nefarious use as
one of the main ingredients in Napalm as a gelling agent (Naphthalene+Palmitate+Gasoline=Napalm)!
Now, here is the really interesting part: that long chain of carbons (red) in the fatty acid
is oil-loving . It dissolves in oil and loves grease. However, the carboxylic acid
group (blue) loves water! Fatty acid salts are the perfect thing to
mix with both oil and water. Such compounds are known as
amphiphiles (from the Greek amphis: both and philia: love, friendship).
When we splash a bit of soap in with some oil and water, the fatty acids organize
around the oil or grease to form "micelles". These are essentially spheres of fatty acids in
which the oil is held at the core of the sphere amongst the oil-loving part of the
micelle, leaving the water-loving exterior of the micelle to mingle with water, thus
dissolving our oil beads into water.
So, making your own soap is not very difficult, but it can be dangerous! Sodium Hydroxide and other bases are caustic and very dangerous to the skin and eyes. Just a splash of Sodium Hydroxide in the eyes can cause severe corneal injuries and blindness. Commercially prepared soaps are pH balanced as the caustic hydroxides are fully reacted.
I hope you enjoyed this month's blog about soap!
