Soap making

Making simple plain soap is relatively easy and involves basic equipment. However, there are certain hazards to workers when making soap, which any potential producer must know about. This article, based on a Technical Brief from Practical Action, describes how you can make simple hard soaps that are suitable for many uses around the home, including hand washing.

Ingredients

There are three main ingredients in plain soap:

• oil or fat (oil is simply liquid fat)
• lye (or alkali)
• water.

Soap recipes include salt, because salt is needed to separate the soap mixture. It does not remain in the soap.

Other ingredients may be added to give the soap a pleasant smell or colour, or to improve its skin-softening qualities. Almost any fat or non-toxic oil is suitable for soap manufacture. Common types include animal fat, avocado oil and sunflower oil. Solid fats and ‘saturated’ oils such as coconut, oil palm and palm kernel are more suitable for soap making. ‘Unsaturated’ oils such as safflower and sunflower may produce soap that is too soft if used alone and are not recommended.

Lyes can either be bought as potassium hydroxide (caustic potash) or sodium hydroxide (caustic soda), or if they are not available, made from ashes. For hard soaps, use sodium hydroxide.

Some soaps are better made using soft water (the kind of water that lathers with soap easily without forming any kind of sediment or scum). For these it is necessary either to use rainwater or add borax (sodium borate, a water softener) to tap or borehole water. Each of the above chemicals is usually available from pharmacies in larger towns.

How to make lye from ashes

To make a small amount of lye, use a porcelain bowl or plastic bucket.

1. Fill the bucket with ashes and add boiling water, stirring to wet the ashes.

2. Add more ashes to fill the bucket to the top, add more water and stir again.

3. Let the ashes stand for 12–24 hours, or until the liquid is clear, then carefully pour off the clear lye. 

Ashes from any burned plant material are suitable, but those from banana leaf or stem make the strongest lye.

The longer the water stands before being drawn off, the stronger the lye will be. Lye that is able to cause a fresh egg to float can be used as a standard strength for soap-making. The strength of the lye does not need to always be the same, because it combines with the fat in a fixed proportion. If weak lye is used, more lye can be added during the process until all the fat is made into soap.

Lye is extremely caustic. It causes burns if splashed on the skin and can cause blindness if splashed into the eye. If drunk, it can be fatal. Be especially careful when adding potash and caustic soda to cold water, when stirring lye water, and when pouring the liquid soap into moulds. Lye produces harmful fumes, so stand back and turn your head away while the lye is dissolving. Do not breathe lye fumes. If possible, use rubber gloves and plastic safety goggles (if you do not have rubber gloves, cover your hands with plastic bags, first checking carefully that the bags have no holes). You should also wear an apron or overalls to protect your clothes. If lye splashes onto the skin or into your eyes, wash it off immediately with plenty of cold water.

When lye is added to water the chemical reaction quickly heats the water. Always add lye to cold water in small quantities at a time.

• Never add lye to hot water because it can boil over and scald your skin.
• Never add water to lye because it could react violently and splash over you.

Because of these dangers, keep small children away from the processing room while soap is being made. Dispose of soap-making wastes carefully outside the house. Do not put them in the drain.

Soap that has just hardened is caustic since the lye has not reacted fully with the fat and become neutralised. This process takes three weeks and is known as curing. When handling soap that has hardened but has not been cured for at least three weeks, wear rubber gloves or cover your hands with plastic bags.

Making hard soap

The method requires three kettles or pans: two small kettles to hold the lye and the fat, and one large enough to contain both ingredients without boiling over.

1. Put the clean fat in a small kettle with enough water or weak lye to prevent burning, and raise the temperature to boiling.

2. Put the diluted lye in the other small kettle and heat it to boiling.

3. Heat the large kettle, and ladle in about one quarter of the melted fat. Add an equal amount of the hot lye, stirring the mixture constantly.

4. Continue this way, with one person ladling and another stirring, until about two-thirds of the fat and lye have been thoroughly mixed together. At this stage the mixture should have the consistency of cream and look the same throughout. A few drops cooled on a glass or ceramic plate should show neither separate globules of oil nor water droplets.

5. Continue boiling and add the remainder of the fat and lye alternately, taking care that there is no excess lye at the end of the process, when the mixture is thick and ropy and slides off the spoon or paddle.

6. Add salt to break up the creamy emulsion (mixture) of oils and lye. The soap then rises to the surface of the lye in granules and looks like milk curd. The spent lye contains glycerine, salt and other impurities, but no fat or alkali.

7. Pour the honey-thick mixture into cloth-lined soap moulds or shallow wooden boxes (the cloth prevents the soap from sticking to the moulds). Alternatively, the soap may be poured into a tub which has been soaked in water overnight to cool and solidify. Do not use an aluminium container because the soap will corrode it. Cover the moulds or tub with sacks to keep the heat in, and let the soap set for 2–3 days.

8. When cold the soap may be cut into smaller bars with a smooth, hard cord or a fine wire. It is possible to use a knife, but care is needed because it chips the soap. Stack the bars loosely on slatted wooden shelves in a cool, dry place and leave them for at least 3 weeks to season and become thoroughly dry and hard.

1) The mixture is poured into a mould lined with cloth. 2) The cold soap can be cut with a wire.

To improve hard soap

Better quality soap may be made by re-melting the product of the first boiling and adding more fats or oils and lye as needed, then boiling again. The time required for this final step will depend on the strength of the lye, but 2–4 hours’ boiling is usually necessary. If pure grained fat and good quality white lye are used, the resulting product will be a pure, hard white soap that is suitable for all household purposes. Dyes, essences or essential oils can be added to the soap at the end of the boiling to colour it or to mask the ‘fatty lye’ smell and give a pleasant fragrance.

Simple kitchen soap

Dissolve 1 can of commercial lye (sodium hydroxide) in 5 cups cold water and allow it to cool. Meanwhile mix 2 tablespoons (30 ml) each of powdered borax and liquid ammonia in half a cup of water. Melt 3 kg fat, strain it and allow it to cool to body temperature. Pour the warm fat into the lye water and, while beating the mixture, gradually add the borax and ammonia mixture. Stir for about 10–15 minutes until an emulsion is formed, and pour the mixture into a cloth-lined mould to cool.

Boiled hard white soap

Dissolve 0.5 kg potash lye in 5 litres of cold water. Let the mixture stand overnight, then pour the clear liquid into a second 5 litres of hot water and bring it to a boil. Pour in 2 kg of hot melted fat in a thin stream, stirring constantly until an emulsion is formed. Simmer for 4–6 hours with regular stirring, and then add 5 litres of hot water in which 1 cup of salt is dissolved. Test whether the mixture is ready by lifting it on a cold knife blade, to ensure that it is ropy and clear.

Further information

There is additional information available in the full Technical Brief:

• How to make soft soap (cold process)
• How to make large quantities of lye
• How to make tallow (animal fat prepared for use in soap making and candle making)
• Additional soap recipes
• Suggested solutions for common problems with soap making
• List of further resources

The Technical Brief was last updated by Tony Swetman. Practical Action uses simple technology to fight poverty and transform lives for the better. The full brief can be downloaded from the website. Go to http://practicalaction.org/practicalanswers and type ‘soap making’ in the search box.