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Soap Making Glossary

Soap Making Glossary

When you start out in the wonderful world of soap making there is lots of terminology that you will need to get your head round. It can be confusing, but you don’t necessarily need to know the language of soap making to start creating your own soap. It will all fall into place over time so don’t run before you can walk. 

To make your life easier and help you out I have put together a handy guide of the most common terms used in soap making. Have a read through and feel free to get in touch if there is anything crucial that you think I might have missed!


According to Wikipedia an alkali is a basic salt of an alkali metal and it can be dissolved in water. An alkali is what you need to turn oils and butters into soap. Sodium hydroxide (NaOH) is an alkali salt and is often called caustic soda. This is used to make bar soap. Potassium hydroxide (KOH) is an alkali salt used to make liquid soap and is commonly called caustic potash. Lye is a generic term for either of these salts.

Caustic Soda

Sodium hydroxide (NaOH) is often called caustic soda. Also known as lye.

Cold Process Soap or CP Soap

Cold process soap is made using the traditional method of soap making which doesn’t involve ‘cooking’ the soap at high temperatures. The only heat involved is purely for melting solid oils (such as coconut) and solid butters (such as shea).


Cold process soap will need at least 4 weeks of curing time to allow the saponification process to complete and it ensures that the soap is ready to use. If used before this process is completed the soap may still be caustic and irritating on the skin. Patience is required here! Don’t worry there is no lye present in cured soap because during saponification the alkalinity of the lye is cancelled out by the acidic oils.

Gel Stage

This is an optional stage in soap making and refers to insulating your soap once poured into the moulds to retain the heat. This is used as it may improve colour and hardness. Some essential oils can cause soap to gel without insulation. Some soap makers try to prevent the gel stage by placing their mould in the refrigerator after pouring the soap.


A biproduct of creating soap is glycerine which is naturally moisturising.  The glycerine is usually removed by commercial soap producers.


This is a generic term for an alkali and is used to refer to Sodium Hydroxide (NaOH).

Lye Discount

This is a term used by soap makers to refer to the lye discount in a soap recipe to leave unsaponified oils in bar soap to provide extra moisturising properties. Lye discount can also be called superfat.


The molecular formula for Sodium Hydroxide.


pH is a scale to measure the acidity or alkalinity of a solution. A pH of 7 is neutral, lower values are more acidic and higher values are more alkaline. The average pH of handmade soap is 9. You can use pH test strips to test the pH of your soap, but these should be used for guidance only as you will not obtain an exact reading.


Saponification is the process by which soap is produced from a solution of oils and lye.  When fatty acids are mixed with lye (sodium hydroxide) at the right temperature there is a chemical reaction and the end result is soap. 

SAP (Saponification) Value

Every oil used in soap making has a saponification value. You will find a SAP chart in most soap making books which lists all the oils and their corresponding values. The number refers to the amount of an alkali solution required to saponify an oil and turn it into soap.

Soda Ash

Soda ash can form on the surface of cold process soap. It is a white powdery residue and totally harmless. There is no fool proof way to prevent it, but you can reduce the likelihood of it forming by spritzing the surface of your soap with surgical spirit after pouring your soap into a mould. 

Sodium Hydroxide

This is an alkali used to make bar soap. It is often called caustic soda and is also known as lye.


This is a term used by soap makers to refer to the extra oils added to a soap recipe to provide extra moisturising properties. You can use a superfat range of between 1 and 8 percent. Superfat can also be called lye discount.


This is the point in making soap where once your oils and lye are mixed together, they start to thicken, and you can drizzle some of the mixture onto the surface and it leaves a trace. You can mix soap to a thin or a thick trace. Once you have reached the trace stage this is where the fun begins, and you can add scents and colours. You must work quickly once you have reached trace stage as the soap will continue to thicken and you need to pour it into your moulds before it gets too thick.  

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