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Lye safety for soap making

All true soap is made by mixing oils and fats with lye. Lye is sodium hydroxide, also sold as caustic soda. It causes deep chemical burns and can blind you in seconds, but it is safe to work with if you respect it every single time. The rules are short, and there are no exceptions.

The four rules

• Goggles on.
• Gloves on.
• Children and pets out.
• Always add the lye to the water, never the water to the lye.

Buying lye

Buy pure sodium hydroxide (99% or higher), with nothing else listed on the label. Do not use drain cleaners. Many contain other chemicals, or aluminium pieces that react dangerously.

Storing it

• Keep it in its original container, or an airtight one clearly labelled as corrosive.
• Never keep it in a food container, where someone could mistake it for sugar or salt.
• Keep it airtight, because it absorbs water from the air.
• Store it high up and locked away.
• Keep it away from aluminium, acids and water.

Protective gear, every time

• splash goggles that seal around the eyes (ordinary glasses are not enough);
• nitrile or rubber gloves that cover the wrists;
• long sleeves, long trousers, an apron and closed shoes;
• hair tied back.

Fresh soap batter is still caustic. Keep the gloves on until the soap is in its mould, and when you cut it in the first days.

Mixing the lye solution

Work outdoors or next to an open window, on a stable surface, with nobody else around.

1. Put on all your protective gear.
2. Weigh the water into a stainless steel or polypropylene jug (marked PP or 5). Never use aluminium or glass.
3. Weigh the lye into a separate, dry container.
4. Add the lye slowly to the water, stirring gently. Pouring water onto lye can make it boil and erupt.
5. Turn your face away. For about a minute the solution gives off fumes that sting the nose and throat.
6. Stir until the lye has dissolved. The solution gets very hot, often 80 to 90 °C.
7. Label the jug and leave it to cool where nobody can knock it over or mistake it for water.

To remember the order, think "snow falls on the lake": the lye goes onto the water.

Spills

• Dry beads: with gloves on, sweep them up at once. They are small and white and easy to miss.
• Spilt solution: keep everyone away, wipe it up with plenty of paper towel, then wash the surface with lots of water.
• Equipment: wash it in plenty of water with gloves on, and keep it only for soap making.

First aid

• On the skin: remove contaminated clothing and flush with cool running water for at least 15 minutes. Get medical help for anything more than a small red patch.
• In the eyes: flush at once with running water for 15 to 20 minutes, holding the eyelids open, while someone phones 10177 or 112. Every lye splash in the eye needs urgent medical attention.
• Swallowed: rinse the mouth and give small sips of water. Do not make the person vomit. Phone the Poisons Information Helpline on 0861 555 777 and get to hospital.

Do not put vinegar on skin or in eyes. Plenty of water is the first aid for lye.

Soap without lye

Melt-and-pour soap base has already been made into soap, so you handle no lye at all. It is the safest way to start.

This guide is based on Chapter 6 of Candle and Soap Making at Home.