Believe it or not, it's still possible to make soap the way that pioneers did, and have it come out quite decently, certainly not as harsh, and even scented with something like essential oils. The process is a long one, and really needs some study of the technique with an emphasis on proper handling of the ingredients, proving, etc.
However, the basics involve the use of fats, and a caustic agent, which is lye or lye water. In the old days, pioneers used fat off the animals they killed and wood ashes. But it wasn't as simple as mixing fat and ash.
It is the reaction of a caustic solution with the fat, which creates the foaming, cleansing effects of soap. And the caustic agent is lye water acquired by pouring rain, also known as “soft" water, through the ashes.
This can involve using an old barrel and packing it one-half full of ash from white wood, which would include white oak or apple wood. Either install a tap at the base of the barrel, or cut a hole that can be snugly sealed with a plug of some kind. Pour rainwater slowly into the barrel, allowing it to seep down through the ashes, when a bit of brown water begins to seep out of the tap or hole, plug it up. Add more ash, dampening it down as you go, until the barrel is full, but the ashes are not floating. Let set for five days.
Drain off water and filter through cheesecloth or other material. Use gloves while working with it, as the caustic water can burn, and must be stored safely away from children and pets, until used. Second and third run-offs can be done, but the lye solution will be weaker. If an egg dropped into the bucket of lye floats about halfway under the water, it is the right strength. If the egg sinks, you can dry boiling the lye water down, until it is stronger.
Chopped beef tallow should be melted in a pot or pan, and cooled. Then place it in another pot with water, to “wash" it. Bring to a boil, set aside to cool, and skim off the cleaned fats. Store in sealed containers.
The proportion of lye to fat is a delicate one, and there are plenty of recipes on the Internet that can direct you in how to estimate your blend, and how to balance the ingredients out when the soap does not form, or is too harsh.
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