Soap

Use hardwood ash — oak, beech, ash, fruitwood. Softwood and conifer ash is resinous and much weaker. Take white ash from a hot fire, sieve out charcoal and nails.

Build a barrel with a false bottom: holes drilled in an inner board, 10 cm of straw or gravel over them, then ash packed to two-thirds, with a tap or a spout at the base. Pour soft rainwater, warm, slowly over the top until it begins to run from the spout, and keep topping up as it drains, over hours. Re-pour the runnings through the same ash two or three times to strengthen it.

Ash lye is potassium hydroxide of unknown strength, and strength decides everything that follows. Two tests, used together:

• Float test: a fresh egg or a small potato floats with a coin-sized patch above the surface. Sinking means too weak; riding high means too strong.
• Feather test: a feather dipped in it begins to dissolve within a minute or two.

Too weak, and boil it down to concentrate it. Too strong, and dilute with measured water. Write the result and the date on the container — lye absorbs moisture from air and weakens in store.

Melt fat at 60–80 °C, never smoking, with a little water in the pan to stop it scorching. Strain through cloth. Then wash it: stir the melted fat into an equal volume of hot water with a handful of salt, let it set, lift the fat off and discard the water beneath with its meat, blood and gristle. Two or three washes.

Unwashed fat makes soap that smells and goes rancid within weeks. Tallow from cattle and sheep gives a harder, longer-keeping soap than pig fat; both work.

Warm the fat to about 50 °C. Add the lye to the fat in a slow stream, stirring constantly — never the other way round. Keep it at a bare simmer and stir for 2–6 hours.

The end point is trace: lift the spoon and the drizzle sits on the surface a moment before sinking, the consistency of thin custard. Keep the fat slightly in excess of the lye — about 5% more fat than the lye can saponify — so no free alkali remains. With ash lye of uncertain strength this is judged by adding lye in small amounts until trace comes, not by a calculated ratio.

Ash lye gives soft, jelly-like potassium soap — perfectly good in a pot beside the washing water, awkward to carry.

For a hard bar, salt it out: stir in salt a handful at a time into the hot soap until it separates into curds floating on a thin brown liquor — the curds rise and can be lifted off, leaving glycerine and surplus lye in the liquor below. Press the curds into a mould. The lasting fix is sodium carbonate instead of potash once you have alkali chemistry.

Fresh soap contains unreacted alkali and burns skin. Cut it into bars, stand them on a rack with air on all sides, out of sun, for 4–6 weeks. Saponification finishes in store, water evaporates, and the bar hardens and lasts far longer in use.

Test before issuing it: rub a wet bar on the inside of a forearm. Any stinging, burning or slipperiness that will not rinse away means it is not cured. A cured bar lathers, rinses clean and leaves no tight, squeaky burn.

Strong lye blinds, and it destroys skin without the immediate pain that would make you pull away. Work outdoors or in a draught, wear eye cover, cover arms and legs, and never lean over the pot.

On skin or in an eye: flush with a large volume of running water for 20 minutes, and keep going for the eye while someone fetches help. Do not neutralise a burn with vinegar — the reaction makes heat in the tissue. Keep vinegar for wiping spills off surfaces and tools instead. Store lye in a labelled, lidded, non-aluminium container out of reach of children; it eats aluminium and gives off hydrogen doing it.

Manufacture without behaviour change buys nothing. Handwashing with soap cuts diarrhoeal disease by roughly 30% and respiratory infection by about 20% — no drug on this site comes close for the effort.

So: a bar and a tippy tap at the latrine and at the kitchen, refilled by a named person. Wash after the latrine, after handling animals, before preparing food, before eating, and before touching a wound or attending a birth. Lather 20–30 seconds, backs of hands, between fingers, under nails. Where soap runs out, wood ash rubbed on wet hands is the traditional substitute; the evidence for it is weaker than for soap, but it beats water alone.