Soap: Background
There was one kind of berry, a dark red.
I tried it, one by one, and hours apart.
Sub-acid, and not bad, no ill effects;
and so I made home-brew. . . .
Home-made, home-made! But aren’t we all?
I felt a deep affection for
the smallest of my island industries.
–Elizabeth Bishop, “Crusoe in England“
(You should actually read the whole poem, as it’s very good. I love how smoothly Bishop’s poetry reads–is that the sort of thing English majors say? In any event, I’m digressing before I start.)
Some time ago, a friend of mine pointed me towards Trader Joe’s Lavender Body Oil. I don’t remember exactly how I came to this thought, but I eventually decided it would be interesting to make soap from this oil, and possibly from others . . .
Eventually I accumulated quite a few “others”:
And so here we go! I’m going to make soap from all the oils in this picture. It’ll be an adventure; my approach will be much closer to Cockeyed.com Science Club than to Angewandte Chemie. (Frankly, I think Rob has much more fun than the Ang. Chem. guys, but don’t tell them that.)
First, some background. I’m going to radically oversimplify the science here, and will probably get some things wrong, but this is essentially what happens.
What we call “fat” is, chemically speaking, almost all triglycerides–molecules formed of a glycerine backbone with three fatty acids attached. If you add water and a base to fat, the fat undergoes a process called hydrolysis, where the glycerine separates out and the fatty acids bond with the base, giving fatty acid salts. This is called saponification. (Check out that last link; it’s from Molecule of the Day, which is made by a guy who actually knows this stuff, and gives a great overview of the saponification process.)
Anyway, saponification is extremely useful, especially for those fatty-acid salts we get out of them. Those salts have split personalities: one end is strongly attracted to water, and the other is strongly attracted to oil. (I’m oversimplifying, as I mentioned.) This means that these molecules are very good at lifting oils and other non-water-like things out of whatever they’re in and into the water, so you can wash them away. These bundles of molecules are called micelles. (Also MOTD, and also worth a look.)
The practical upshot of all this is 1) you can make soap if you add a base to a fat and 2) you can clean things with said soap. The only real gotcha here is that the best bases for making soap, like lye, are not terribly friendly to the skin, as anyone who has seen Fight Club can testify. (The first time I saw Fight Club, I was in an airplane flying over the Atlantic Ocean. Anyway.)
So you need to know how much lye you need to react with whatever amount of oil you’re using. Fortunately, this is easy to find–it’s called the saponification number. There are all kinds of tables of these numbers on the Internet, as well as calculators for determining how much of all the ingredients you need. Also, this site explains all this with a cute story involving bunnies, wolves, border collies, and sheep.
Prior: A Conversation at Safeway Regarding Soap.
Next: olive oil, coconut oil, and a mixture.
2 comments September 2nd, 2006
