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At the dawn of the twenty-first century there remains in the world a small but dedicated sub-culture of people who are not afraid to experience the joys of manufacturing; a hardy folk for whom the word chemical is not equated with "evil poison foisted on unsuspecting innocents by heartless multi-national corporations;" a people who recognize that something as good and wholesome as soap requires for its manufacture something as caustic and poisonous as caustic soda. I speak, not of industrial or laboratory chemists, but of soapers—crafters who in an age of pre-packaged conveniences indulge in the simple pleasure of making soap from scratch.
The first choice of the soap-maker is that of which fat to saponify. You can use any fat or oil derived from animal or vegetable sources; mineral and motor oils are not triglycerides and so are not useful for making soap. Among animal fats, you may choose tallow rendered from beef, lard from pork, or suet from goat. Butter and bacon grease make perfectly functional soaps, though they will win no prizes for their aromas. Among vegetable oils, olive oil has been the traditional choice for fine soap. Palm oil is renowned for its rich lather. Other vegetable oils are often used in combination with tallow or lard rather than by themselves. Even vegetable shortening and margarine can be used, though the soft, whipped, or tub margarines contain excess water, complicating the calculation for the amount of caustic soda to be used. Each fat lends its own particular qualities to the finished soap and experienced soapers blend different oils to produce the qualities they desire, but for a first soap I recommend using any of those listed in Table 19-1.
The next choice of the soap-maker is that of which alkali to use. Potassium hydroxide will produce a soft or liquid soap, while sodium hydroxide will produce the familiar solid bar. Either of these alkalis might be manufactured from scratch, using potash or soda from Chapter 8 and lime from Chapter 10 to produce caustic soda or caustic potash as described in Chapter 15. Recall from Table 8-1, however, that 1000 pounds of wood provide only about a pound of potash. Consider as well that caustic soda is sold as a drain opener, and so it is frequently available in grocery stores and hardware stores. For these reasons, store-bought caustic soda (lye) is the choice of most soapers.
You want 100% sodium hydroxide; name-brand drain openers contain perfumes or other ingredients which may interfere with saponification. Many grocery stores have removed lye from their shelves in the mistaken belief that it is more dangerous than the name-brand drain openers. And while lye deserves all of the dire warnings on its label, you will find the same warnings on the name brands because they are almost universally either sodium hydroxide or sulfuric acid. You would do the world of soapers a service by pointing this out to grocery store managers when the opportunity arises; we all benefit from cheap and convenient sources of lye.
The traditional method for making soap, the hot process, involves leaching ashes to get alkali, causticizing the alkali with lime to make caustic soda, and boiling the resulting lye with fat to make soap. It turns out that the boiling step has less to do with saponification than with removing bejeezical water to concentrate the lye. We can skip the boiling step if we start with solid caustic soda. This cold process is the method preferred by the majority of modern amateur soap-makers.
For your first soap, I recommend a cold process using that container of choice for caveman chemists, the 2-liter pop bottle, which will accommodate between one and two pounds of fat. Weigh out your fat on a balance and record the weight in your notebook. Place it in a beaker or a saucepan and warm it on a hot-plate until it melts (if solid) or until it is warm to the touch (if liquid). While your fat is warming, use UFA and Table 19-1 to answer the following question:
If you are blending different fats and oils you can answer this question for each one separately and then add the weights to get the total weight of caustic soda. Multiply the total weight of caustic soda by a factor of 0.95; it is far better to have a finished soap with excess fat than one with excess caustic soda. Weigh out your caustic soda on a balance and record the weight in your notebook. Weigh out twice that amount of water in a glass measuring cup or beaker and record the weight in your notebook. Stirring with a glass rod or plastic spoon, slowly add your caustic soda to your water—if you add water to caustic soda, the caustic soda will cake up and dissolve more slowly. The water will get hot as the caustic soda dissolves. Continue stirring until the caustic soda is completely dissolved. By this time, you should have hot melted fat on the stove and hot caustic soda solution in a beaker.
They say that a watched pot never boils, but it never cools either. You are about to mix the oil and caustic soda solution together, but as with salad dressing, oil and water don't mix. This is especially true of hot oil and water, so you will get the best results if you allow both ingredients to cool down to between 38 and 43°C, 100 and 110°F. A thermometer will keep you honest, but as long as you can hold them in your bare hands comfortably, you are probably alright. In my experience, the most frequent reason for failed soap is that the soaper got impatient and mixed the oil with the caustic soda too soon.
When the fat and caustic soda have cooled sufficiently, use a funnel to pour the fat into your 2-liter pop bottle. Add the caustic soda solution, put the cap on the bottle and give it a few shakes. You now have what amounts to caustic salad dressing—the oil and water mix initially, but may separate over time. As long as the mixture is smooth and creamy, you are fine, but if it begins to separate, give the bottle another shake. When the mixture no longer separates, you can let it rest. A tallow or shortening soap may solidify in an hour or so; a lard or olive oil soap may take up to two days.
The saponification will proceed more quickly if the mixture is kept warm than if it is allowed to cool. Because the saponification reaction is exothermic, simply insulating a large batch of soap is sufficient to keep it warm, but a small batch may need some help. I like to place my sealed 2-liter bottle in a pot of hot tap water to keep it warm. Don't watch this pot or fret about it, but whenever it occurs to you in the first couple of days, replace the water with hot tap water. If you forget to change the water, it's no big deal—the soap may just take a little longer to cure.
The curing time will vary from one fat to another, but after a week your soap should be ready for testing. With a knife, slit the pop bottle open and peel it apart to release your soap. If you have done your work correctly, you will have a single solid cake of soap with very little extraneous water. Cut a sliver the size of a raisin from this cake and place it into an empty bottle with a cup or so of hot water. Put the cap on the bottle and shake it. If you have succeeded in making soap, the bottle will fill with soap suds after a bit of shaking. If it doesn't, then either you had too little caustic soda in your mixture or the soap is not sufficiently cured. As a second test, wipe a piece of wet pH test paper against your soap. If it turns blue, then either you had too much caustic soda in your mixture or the soap is not sufficiently cured. If your soap fails either of these tests, allow it to cure for a few more days and then test it again. When your soap is finished, you can slice it into bars of a convenient size.
With a bottle of soap suds, you can explore one more aspect of soap manufacture. Make a good, strong soap solution and add some salt to it. The fatty acid salts are less soluble in salt water than they are in fresh water and so they will precipitate from the solution. The soap, that is, the fatty acid salts will float to the top while the glycerol stays in solution. Separating the above from the below allows us to produce glycerol as a by-product of soap manufacture. Glycerol will be an important player in the development of explosives and plastics, as we shall see in Chapter 27.
Record the weights of the fat, caustic soda, and water that went into your pop bottle and compare these to the weight of the soap you produced. The soap is satisfactory if it makes suds and has a pH no higher than 8. Tape your yellow or green pH test paper into your notebook as a keepsake.