Unlike the bars of toxic ick the grocery store sells, natural soap is made from three main ingredients: fat, water, and lye.
"But lye is caustic! I use it to clean my drain, for goodness sake!", you might say. You might also say, "Fat? Your soap is made from fat? How am I supposed to get grease off my hands with fat?"
Both are excellent questions. The answer to both questions is a single word: saponification.
Turns out that when fats (also known as lipids) are mixed with lye (a strong alkaline, or base), an interesting chemical reaction occurs that results in no lye and no fat. What is left after this reaction is soap. This reaction has a name: saponification. It's a very simple reaction that people have known about for centuries.
Legend has it that we get the word "soap" from Italy's Mt. Sapo, near Rome. The women washing clothes in the river found that their clothes got much cleaner at one particular spot for some reason. Well, that reason was easy to explain. Farther up the mountain is where they sometimes sacrificed and burned animals. The fat from the animals would run downhill, and water would wash the ashes from the fire. So now we have our three ingredients: fat from the animals, an alkaline from the ashes (in this case, potassium hydroxide, or potash) and water.
Whether this is truth or legend, many languages derive their names for the product from the word sapo. In Italian it’s called “sapone”, French “savon” and English, it's “soap”.
But soap, by other names, has been mentioned much farther back than that. Sumerian clay tablets dating back to 2,500 BC mention a formula for soap that consists of cassia oil, alkali, and water.
The chemistry hasn't changed much in the past five thousand years. But we've gotten better at controlling the process. More on that in a later post.