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Make Cold Process Soap

 Make Cold Process Soap

Making cold process soap is ideal for those crafters that want to have full control of every ingredient. It is made by combining oils with sodium hydroxide (lye). This causes a chemical reaction known as ‘saponification’. 

Please refer to the soap making glossary for extra assistance on terminology. 


safety goggles soap making


Making soap from scratch is fun and amazing but there is also a serious side to it.

Making soap with the cold process method involves using strong alkali ie: caustic soda, which is dangerous if not used correctly. It can result in severe burns to the body and can be fatal if it is ingested.

With this in mind, before we consider materials, process and equipment we must mention.... 



  • Store lye (caustic soda) up high in a sealed, secure and correctly labelled container away from children and animals. Lye is highly corrosive.

  • Never allow children or pets in the work area. Lye is poisonous and corrosive - it will burn skin.

  • Never leave lye water unattended. Thirsty animals don’t understand what it is and children are curious.

  • Never add water to the lye. Always pour lye/ caustic soda into the water. Doing this incorrectly risks generating heat which can cause the glass to crack or explode.

  • Call Emergency if anyone ingests lye or splashes it in their eyes.
    • Do not wash your soap mix directly down the drain when cleaning up. Instead, allow the mix to harden and scrape remnants into a bag that can be put in the rubbish once tied. Washing it down the drain risks clogging your sink and is bad for the waterways.

    • Do not use your dishwasher for cleaning soap making related equipment. Do not use soap equipment for food.

    • Always mix your lye water outside, or in a well-ventilated area, to avoid inhaling the fumes.

    • Wear gloves and long sleeves. If lye water or raw soap gets directly on your skin, wash the area immediately with cold water for fifteen minutes. You can also attempt to neutralise with water and vinegar. The lye water will immediately cause a corrosive action to your skin leaving redness and scarring.

    • Wear safety googles that protect the eyes from all angles. Normal glasses are not enough. You can get safety goggles that fit over prescription glasses. If you forget to wear goggles and splash lye water in your eyes, clean them with running water and go to your nearest ER. Do not rub.

    • Do not use aluminium vessels in soap making.  Lye and raw soap also should not come into contact with teflon, copper, iron and tin, because alkalis will destroying or melt them.  Tempered glass can be used to pour your combined oils and lye water at trace, but not for lye water on its own.  Also do not use plastics like PET, PC, nylon, PS#6 or ABS when working with lye solution or raw soap batter. To read more about this please visit our blog here.

    • Don't fill your soap pot more than half full.
    • Always test soap before selling or giving it away.



    Here is a list of suggested equipment. Equipment used for soap making should not be used for food. Lye and fragrance can stay in cracks even after washing. 

    • Gloves: 
    Always wear protective gloves. You will use lye which is corrosive. That means it can burn the skin. Rubber dish gloves to the elbow are ideal but bulky. Or thinner latex gloves are fantastic too. So long as you cover the rest of your arms with a long sleeve top. Not doing so risks scarring to your skin.
    • Goggles: 
    Lye can burn your eyes so you must wear safety goggles that protect your eyes from all angles. If you wear glasses, wear safety gogglers over them.
    • Heat Safe Glass, Plastic or Stainless Steel Containers. 
    Do not use aluminium as it will react with the lye and make toxic fumes. 
    • Stick Blender: 
    A whisk will take a long time, so a stick blender can shorten the process.
    • Silicone Spatulas: 
    To scrape the last bits of soap out of the container and into the mould. Also useful for smoothing the top. Not wooden.
    • Scale:
    For measuring by weight, digital preferred.
    • Soap Moulds: 
    Silicone, plastic or wood or long-life milk cartons.
    • Heavy duty plastic bucket
    To mix the lye and distilled water. Polypropylene (PP#5) is a hard, heat resistant container and is lye- resistant. Check the bottom of the container for the PP#5 stamp. 
    • Measuring Jugs 
    • Paper Towels
    • Hand held Thermometer
    • Soap Moulds
    • Whisk
    • A Bucket Of Water & A Bottle Of Vinegar: 
    to neutralise spills on skin  



      Step 1:

      Put On Your Safety Gear And Gather Your Ingredients:

      You will need:

          1. Oils eg: coconut, olive, rice brain depending on your recipe
          2. Lye i.e: sodium hydroxide / caustic soda (must be 98% pure). Caustic soda is also used for drain cleaning, so it can often be found in a hardware store. However, most of these products are not 98 percent pure.
          3. Essential oil/fragrance oil - must be skin safe
          4. Soap Colour, if you choose
          5. Distilled water / rain water
          6. Rosemary extract - if you want to add a natural preservative / antioxidant which helps extend product shelf life and prevent brown spots forming over time from oxidation.


      Step 2:

      Set Up Your Workspace & Prepare The Lye


      preparing lye cold cold process soap making


      Prepare your area.

      Measure all the ingredients (oils, fragrance etc) according to the recipe and set them aside. That way everything is nicely organised so you can focus on the soap making.


      lye cold process soap


      Be sure to take the lye to a well-ventilated area or outside where you do not inhale the fumes!

      Very important! Ensure you add the lye to the water, not the other way around! So fill your container with water first. Then add the lye to the water. Only use a heat tempered glass container if you are using glass. Alternatively use a heat resistant propylene (PP) container. It is best to use distilled water or rain water.

      Weigh your caustic soda in a separate container.

      When you are slowly adding caustic soda to the water, gently stir until all the caustic soda has dissolved and your liquid is clear. This is what is referred to as ‘lye water’.

      Place your container which is filled with lye water in the water filled sink and leave it to cool down. You can quarter fill the sink with cold water to speed up this cooling process. The cool sink water will slowly start to warm up as the lye water cools. 

      Once your lye water has cooled to approximately 40 degrees C,  the fumes will cease and you can then take it back inside. Never leave lye water unattended in case of pets or children.


      make your own soap 

      Step 3:

      Combine Oils with Lye Water

      (until the mixture reaches trace)

      Once your lye water has reached approximately 25 degrees C you can combine it with your oils. Combine all your oils and heat them, checking with a thermometer.

      Note: If your coconut oil is solid, you can melt it on its own in the microwave or over your cooking element to liquify it first.


      temperature check soap making


      When the oils and the lye are both at the same temperature, pour the lye into the container containing all of the oils. Ensure that your goggles are still on in case of splashing.

      Activate your stick blender into the pot. Pulse gently, as too much blending with speed up the process too quickly. The mixture will take on a milky, custard like appearance and will thicken. This is called ‘trace’. If you’re unsure if the mixture has reached trace, drizzle a small amount of the mixture on top of itself to test. It should stay on the surface.


      stick blender soap making


      Step 4:

      Add Colour And Fragrance


      adding fragrance to soap


      Add colour and then skin safe fragrance (fragrance measures 2.5-4% of the oil weight) being aware that your chosen fragrance oil may accelerate trace (make the mixture too thick) if you use the stick blender too much. You can switch to a handheld whisk if you like. If the mixture is too thick or ‘seizes’ , this might make the mixture difficult to pour into moulds.

      Heating the fragrance before adding it can also help to avoid accelerating trace for particular fragrances. You can also add the fragrance into oil first, and then add that to the mixture to avoid acceleration and seizing. Avoid inhaling the powerful fumes of the added fragrance in the soap mix. Only once the soap has ‘cured’, the fragrance will be at the correct level.


      Step 5:

      Time To Pour

      Pouring soap making


      Pour the soap mix into the moulds and tap the mould to release any air bubbles.

      Cover the soap moulds in cling wrap.

      You might like to wrap the moulds in a blanket to force ‘gel phase’. You can also place them in an insulated box.

      Leave any remaining mix in your pot to harden and scrape into a tied plastic bag the following day wearing gloves, to be disposed of in the rubbish, before washing your pots and equipment.

      Leave the soap in the moulds for at least a few days or until it hardens a bit. 


      Un-Mould And Enjoy!


      Un-mould the soap 2-4 days later.

      You can cut into the soap if required.

      Place the soap on curing racks for 4-6 weeks to enable evaporation of all water and lye, ensuring a nice hard bar. If you use your soap and there is still un-evaporated lye in the soap bar, it will aggravate or burn your skin.

      Test your soap before selling or giving it away.


       Now that you understand the basics of cold process soap making works, give it a go!

      Choose a recipe online using the oils that appeal to you, or try creating your own recipe using our SAP guide.

      If you're still not feeling confident, book in to one of our cold process soap making workshops.