Soap from lard and tallow, step by step

1. How soap is made

Fat and lye combine into soap and glycerine. That is why there is no "roughly" here.

1. Clean fat — Lard and tallow must be rendered, without salt or bits of meat. Fat that hasn't been cleaned gives a soap that smells and goes rancid.
2. Caustic soda — For hard bar soap, buy pure caustic soda (99 % NaOH) as beads or flakes, with a label showing the contents. In the US, check that "100 % lye" really says sodium hydroxide only.
3. Soft water — Distilled, rainwater, or boiled and cooled water. Hard well or tap water gives a cloudy soap and white deposits.
4. 5 % superfat — You use 5 % less lye than it would take to turn all the fat into soap. One kilogram (2.2 lb) of fat gives roughly 10–12 bars of 100–120 g (about 4 oz).

Why: Lye pulls the fatty acids away from the glycerine and turns them into soap. The glycerine stays in the soap and makes it mild on the skin.

• Don't use drain cleaner: it often contains aluminium shavings, dyes and other additives.
• Soap for sale is a cosmetic product (or, in the US, may be a consumer product) with its own rules. Check with the competent authority where you live.

2. Working safely with lye

NaOH burns skin and eyes. You keep five rules every single time.

1. Goggles and gloves — Safety goggles that fit close to the face, rubber or nitrile gloves, long sleeves, closed shoes and an apron.
2. Lye into water — Always pour lye into water, never water onto lye: water on dry lye boils on the spot and throws it into your face. "Snow falls on the lake."
3. Air and water — Dissolve it outdoors or by an open window and don't breathe the fumes for the first 1–2 minutes. Clean water for rinsing stands on the table.
4. No aluminium — Use only stainless steel or hard plastic, PP (5) or HDPE (2). Lye eats aluminium and gives off flammable hydrogen. Children and pets out of the room.

Why: In the eye, lye can permanently damage the cornea within seconds. As it dissolves, the water heats up to 80–90 °C (175–195 °F) and gives off sharp fumes.

• Lye in the eye: rinse with lukewarm running water for at least 15–20 minutes, eyelids open, then go straight to eye casualty or the emergency department. No vinegar.
• Keep NaOH in its original container, locked away from food, marked LYE, NaOH, DO NOT TOUCH.

3. Calculating the recipe · Locked

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4. Cold process · Locked

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5. Cutting and curing · Locked

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6. Additives and laundry soap · Locked

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